In our daily lives, objects such as birds, fish, and cars can be either at rest or in motion. Motion is observed when an object’s position changes over time. Sometimes, motion is inferred indirectly, like noticing dust moving to deduce air movement. Perception of motion can vary: passengers in a moving bus see trees moving backward, while onlookers outside the bus see both the bus and its passengers in motion.
Motion
Describing Motion
To describe an object’s motion, we use a reference point, or origin, as a fixed location. For instance, if a school is 2 km north of a railway station, the railway station is the reference point. This origin helps us measure and describe the object’s position relative to it.
What is Motion?
A body is said to be in a state of motion when its position changes continuously with reference to a point. Motion can be of different types depending upon the type of path by which the object is travelling through:
Types of Motion
Circulatory motion/Circular motion: In a circular path.
Linear motion: In a straight-line path.
Oscillatory/Vibratory motion: To and fro path with respect to origin.
Motion Along a Straight Line
The simplest type of motion is along a straight line. Let’s understand this with an example. Imagine an object moving along a straight path, starting from point O, which we use as the reference point.
Motion along a straight line
Example Description
Initial Motion: The object starts at point O and moves to point A via points C and B.
Return Motion: The object then travels back from A to C through B.
Distance Covered
The total path length covered by the object is the sum of the distances traveled:
Distance from O to A: 60 km
Distance from A to C: 35 km
Total Distance from O to C = OA + AC = 60 km + 35 km = 95 km
Distance is a scalar quantity, meaning it only has magnitude and no direction.
Scalar quantity: It is the physical quantity having its own magnitude but no direction. Example: Distance, Speed.
Vector quantity: It is the physical quantity that requires both magnitude and direction. Example: Displacement, Velocity.
Distance and Displacement
1. Distance
The actual path of length travelled by an object during its journey from its initial position to its final position is called the distance.
Distance is a scalar quantity that requires only magnitude but no direction to explain it.
Example: Ramesh travelled 65 km. (Distance is measured by odometer in vehicles.)
2. Displacement
The shortest distance travelled by an object during its journey from its initial position to its final position is called displacement.
Displacement is a vector quantity requiring both magnitude and direction for its explanation.
Example: Ramesh travelled 65 km southwest from Clock Tower.
Displacement can be zero (when the initial point and final point of motion are the same) Example: Circular motion.
Example of Zero Displacement
Try yourself:What is the definition of distance?
A.A body is said to be in a state of rest when its position does not change with respect to a reference point.
B.A body is said to be in a state of motion when its position changes continuously with reference to a point.
C.The actual path of length travelled by an object during its journey from its initial position to its final position.
D.The physical quantity that requires both magnitude and direction.
Example 1: A body travels in a semicircular path of radius 10 m starting its motion from point ‘A’ to point ‘B’. Calculate the distance and displacement.
Sol. Given, π = 3.14, R = 10 m
The distance is the length of the semicircular path.
Distance = Circumference of a circle ÷ 2
Distance = 2πR ÷ 2
Distance = πR = 3.14 × 10 = 31.4 m
Where as ,
Displacement = 2 × R = 2 × 10 = 20 m
Example 2: A body travels 4 km towards North then he turns to his right and travels another 4 km before coming to rest. Calculate
(i) total distance travelled,
(ii) total displacement.
Sol. The total distance is the sum of all the paths travelled:
Total Distance = 4km (North) + 4km (Right) = 8km
Since displacement is the shortest straight-line distance between the starting point and the final point.
The path forms a right triangle, where:
One leg = 4 km (North direction),
Other leg = 4 km (Right direction).
Try yourself:What is the difference between distance and displacement?
A.Distance is a vector quantity, while displacement is a scalar quantity.
B.Distance requires both magnitude and direction, while displacement only requires magnitude.
C.Distance is measured in kilometers, while displacement is measured in meters.
D.Distance is the actual path traveled by an object, while displacement is the shortest distance between the initial and final positions.
Uniform and Non-uniform Motion
1. Uniform Motion
When a body travels equal distances in equal intervals of time, then the motion is said to be a uniform motion.
2. Non-uniform Motion
In this type of motion, the body travels unequal distances in equal intervals of time.
Two types of non-uniform motion: (i) Accelerated Motion: When the motion of a body increases with time. (ii) De-accelerated Motion: When the motion of a body decreases with time.
Measuring the Rate of Motion
The measurement of distance travelled by a body per unit of time is called speed. i.e. Speed (v) = Distance Travelled/Time Taken = s/t
SI unit:m/s (meters/second)
If a body is executing uniform motion, then there will be a constant speed.
If a body is travelling with a non-uniform motion, then the speed will not remain uniform but have different values throughout the motion of such a body.
For non-uniform motion, the average speed will describe one single value of speed throughout the motion of the body. i.e. Average speed = Total distance travelled/Total time taken
Conversion Factor Change from km/hr to m/s = 1000m/(60×60)s = 5/18 m/s
Example: What will be the speed of body in m/s and km/hr if it travels 40 km in 5 hrs? Sol: Distance (s) = 40 km Time (t) = 5 hrs. Speed (in km/hr) = Total distance/Total time = 40/5 = 8 km/hr 40 km = 40 × 1000 m = 40,000 m 5 hrs = 5 × 60 × 60 sec. Speed (in m/s) = (40 × 1000)/(5×60 ×60) = 80/36 = 2.22 m/s
Speed with Direction
It is the speed of a body in a given direction.
The measurement of displacement travelled by a body per unit of time is called velocity. i.e.Velocity = Displacement/Time
SI unit of velocity: ms-1
Velocity is a vector quantity. Its value changes when either its magnitude or direction changes.
It can be positive (+ve), negative (-ve) or zero.
For non-uniform motion in a given line, average velocity will be calculated in the same way as done in average speed. i.e.Average velocity = Total displacement/Total time
For uniformly changing velocity, the average velocity can be calculated as follows:-
Avg. Velocity (vavg) = (Initial velocity + Final velocity)/2 = (u+v)/2 where, u = initial velocity, v = final velocity
Example 1: During the first half of a journey by a body it travels with a speed of 40 km/hr and in the next half it travels at a speed of 20 km/hr. Calculate the average speed of the whole journey.
Sol: The average speed for a journey where the distances are equal but the speeds are different is not simply the arithmetic mean
When a body covers equal distances at different speeds, the correct formula for average speed is: Given:
Speed during the first half (v1) = 40 km/hr
Speed during the second half (v2) = 20 km/hr
Now, use the correct formula:
Example 2: A car travels 20 km in first hour, 40 km in second hour and 30 km in third hour. Calculate the average speed of the vehicle.
Sol: Speed in 1st hour = 20 km/hr
Distance travelled during 1st hr = 1 × 20= 20 km
Speed in 2nd hour = 40 km/hr
Distance travelled during 2nd hr = 1 × 40= 40 km
Speed in 3rd hour = 30 km/hr
Distance travelled during 3rd hr = 1 × 30= 30 km
Average speed = Total distance travelled/Total time taken
= (20 + 40 + 30)/3 = 90/3 = 30 km/hr
Try yourself:What is the definition of uniform motion?
A.When a body travels unequal distances in equal intervals of time.
B.When a body travels equal distances in equal intervals of time.
C.When the motion of a body increases with time.
D.When the motion of a body decreases with time.
Rate of Change of Velocity
Acceleration is seen in non-uniform motion and it can be defined as the rate of change of velocity with time. i.e. Acceleration (a) = Change in velocity/Time = (v-u)/t where, v = final velocity, u = initial velocity
Here, v > u, then ‘a’ will be positive (+ve). If v is greater than u, then acceleration (a) will be positive.
Example: A car speed increases from 40 km/hr to 60 km/hr in 5 sec. Calculate the acceleration of car. Sol. u = 40km/hr = (40×5)/18 = 100/9 = 11.11 m/s v = 60 km/hr = (60×5)/18 = 150/9 = 16.66 m/s t = 5 sec a = (v-u)/t = (16.66 – 11.11)/5 = 5.55/5 = 1.11 ms-2
Try yourself:Which quantity requires both magnitude and direction.
A.Distance
B.Displacement
C.Speed
D.None of these
Retardation/Deceleration
Deceleration is seen in non-uniform motion during decrease in velocity with time. It has same definition as acceleration. i.e. Deceleration (a’) = Change in velocity/Time = (v-u)/t
Here, v < u, ‘a’ = negative (-ve).
Example: A car travelling with a speed of 20 km/hr comes into rest in 0.5 hrs. What will be the value of its retardation? Sol. v = 0 km/hr, u = 20 km/hr, t = 0.5 hrs Retardation, a = (v-u)/t = (0-20)/0.5 = -200/5 = -40 km hr-2
Graphical Representation of Motion
1. Distance-Time Graph (s/t graph)
(i)s/t graph for uniform motion: (ii)s/t graph for non-uniform motion: (iii) s/t graph for a body at rest: v = (s2 – s1)/(t2 – t1) But, s2 – s1 ∴ v = 0/(t2 – t1) or v = 0
2. Velocity-Time Graph (v/t graph)
(i) v/t graph for uniform motion: a = (v2 – v1)/(t2 – t1) But, v2 – v1 ∴ a = 0/(t2 – t1) or a = 0 (ii) v/t graph for uniformly accelerated motion:
In uniformly accelerated motion, there will be an equal increase in velocity in equal intervals of time throughout the motion of the body. (iii) v/t graph for non-uniformly accelerated motion: a2 ≠ a1 (iv) v/t graph for uniformly decelerated motion: a1‘ = a2‘ (v) v/t graph for non-uniformly decelerated motion:
Note: In v/t graph, the area enclosed between any two time intervals, t2 – t1, will represent the total displacement by that body.
The displacement can also be calculated as the area of the trapezium formed by the v/t graph:
= Area of ∆ABC + Area of rectangle ACDB = ½ × (v2 – v1)×(t2 – t1) + v1× (t2 – t1)
Example: From the information given in the s/t graph, which of the following body ‘A’ or ‘B’ will be faster? Sol. vA > vB
Try yourself:Which of the following statements is true about acceleration?
A.Acceleration is only seen in uniform motion.
B.Acceleration is the rate of change of velocity with time.
C.Acceleration is always negative.
D.Acceleration is the rate of change of distance with time.
Equations of Motion by Graphical Method
Also read: NCERT Solutions: Motion
1. First Equation: v = u + at
Final velocity = Initial velocity + Acceleration × Time Graphical Derivation Suppose a body has initial velocity ‘u’ (i.e., velocity at time t = 0 sec.) at point ‘A’ and this velocity changes to ‘v’ at point ‘B’ in ‘t’ secs. i.e., final velocity will be ‘v’.
For such a body there will be an acceleration. a = Change in velocity/Change in Time ⇒ a = (OB – OA)/(OC-0) = (v-u)/(t-0) ⇒ a = (v-u)/t ⇒ v = u + at
2. Second Equation: s = ut + ½ at2
Distance travelled by object = Area of OABC (trapezium) = Area of OADC (rectangle) + Area of ∆ABD = OA × AD + ½ × AD × BD = u × t + ½ × t × (v – u) = ut + ½ × t × at ⇒ s = ut + ½ at2 (∵a = (v-u)/t)
3. Third Equation: v2 = u2 + 2as
s = Area of trapezium OABC
Example 1: A car starting from rest moves with a uniform acceleration of 0.1 ms-2 for 4 mins. Find the speed and distance travelled. Sol: u = 0 ms-1 (∵ car is at rest), a = 0.1 ms-2, t = 4 × 60 = 240 sec. v = ? From, v = u + at v = 0 + (0.1 × 240) = 24 ms-1
Example 2: The brakes applied to a car produces a deceleration of 6 ms -2 in the opposite direction to the motion. If a car requires 2 sec. to stop after the application of brakes, calculate the distance travelled by the car during this time. Sol: Deceleration, a = − 6 ms-2; Time, t = 2 sec. Distance, s =? Final velocity, v = 0 ms-1 (∵ car comes to rest) Now, v = u + at ⇒ u = v – at = 0 – (-6×2) = 12 ms-1 s = ut + ½ at2 = 12 × 2 + ½ (-6 × 22) = 24 – 12 = 12 m
Try yourself:A car is moving with an initial velocity of 20 m/s. If it accelerates at a rate of 5 m/s? for 4 seconds, what is its final velocity?
A.15 m/s
B.40 m/s
C.35 m/s
D.45 m/s
Uniform Circular Motion
If a body is moving in a circular path with uniform speed, then it is said to be executing the uniform circular motion.
In such a motion the speed may be the same throughout the motion but its velocity (which is tangential) is different at each and every point of its motion. Thus, uniform circular motion is an accelerated motion.
Direction at different points while executing circular motion
Have you ever wondered how your body moves, breathes, or even thinks? All these activities are possible because our body is made up of tiny building blocks called cells. All living organisms are made up of cells, which are the basic units of structure and function in life.
In unicellular organisms like Amoeba, a single cell performs all essential functions such as movement, food intake, breathing, and waste removal.
In contrast, multicellular organisms have millions of cells, each specialised to do a particular job efficiently. For example, in humans, muscle cells help in movement, nerve cells carry messages, and blood cells transport substances like oxygen and food. In plants, vascular tissues like xylem and phloem help move water and food throughout the plant.
In multicellular organisms, cells with similar jobs group together to form tissues. A tissue is a group of cells that are similar in structure and work together to perform a specific function. Examples of tissues include blood, muscle, and phloem. Grouping cells into tissues helps the body work more efficiently, as each tissue takes care of a certain task.
Tissue
Are Plants and Animals Made of the Same Types of Tissues?
Plants and animals are made up of different types of tissues, each serving specific roles that match their way of life.
1. Structure and Movement:
Plants: Plants stay in one place and need a strong structure to support themselves. Their supportive tissues, which mainly consist of dead cells, provide rigidity.
Animals: Animals are mobile, moving around to find food, mates, and shelter. Their tissues are mostly living and specialised, allowing for movement and flexibility.
2. Growth Patterns:
Plants: Plants grow in specific areas called meristems, where new cells are formed continuously. Once certain parts mature, they stop growing.
Animals: In contrast, animals grow more evenly, without clear areas of active and inactive cell division.
3. Complexity and Specialisation:
Plants: Plant tissues are divided into two main categories: meristematic and permanent. Meristematic tissue is for growth, while permanent tissues include simple types (like parenchyma, collenchyma, and sclerenchyma) and complex types (such as xylem and phloem).
Animals: Animal tissues are classified into four main types: epithelial, connective, muscular, and nervous tissues. Epithelial tissue is further divided based on shape and function into squamous, cuboidal, columnar, ciliated, and glandular types. Connective tissues consist of areolar, adipose, bone, tendon, ligament, cartilage, and blood. Muscle tissues include striated, unstriated, and cardiac types. Nervous tissue is made up of neurons that transmit signals.
Plant Tissues
Plant tissues are classified into two main types: meristematic and permanent.
Meristematic Tissue: This is the dividing tissue present in the growing regions of the plant.
Permanent Tissues: These are derived from meristematic tissue once they lose the ability to divide. Permanent tissues are further classified into simple and complex tissues.
The three types of simple tissues are:
Parenchyma
Collenchyma
Sclerenchyma
The two types of complex tissues are:
Xylem
Phloem
1. Meristematic Tissue
Meristematic tissue is the growth tissue found in the areas of the plant that are still developing. The growth of plants happens in specific areas because of this special tissue that divides.
These cells are small, round, or polygonal with dense cytoplasm. They are very active and have thin cellulose walls and noticeable nuclei. They do not have vacuoles.
Meristematic tissues can be classified based on their location:
Apical Meristem: Found at the tips of stems and roots, this type increases the length of both.
Lateral Meristem (cambium): Located on the sides of stems and roots, it helps to thicken them.
Intercalary Meristem: Found near the nodes (the points on a stem where leaves or branches grow). It contributes to the length between two nodes.Intercalary meristem section
Longitudinal section of shoot apex showing location of meristem and young leaves
Try yourself:
Which type of meristematic tissue is responsible for increasing the length of stems and roots?
A.Apical Meristem
B.Lateral Meristem
C.Intercalary Meristem
D.None of the above
2. Permanent Tissues
Permanent tissues come from meristematic cells that can no longer divide. These cells change to take on specific roles. They can be either living or dead, and their walls can be thin or thick, with the thickening being either regular or irregular.
Permanent tissues are further divided into two main groups: Simple Permanent Tissue and Complex Permanent Tissue.
Simple Permanent Tissue
A few layers of cells beneath the epidermis are generally known as simple permanent tissue.
This type consists of one kind of cell that serves the same function. The three types of simple tissues are:
Parenchyma
Collenchyma
Sclerenchyma
Complex permanent tissues are made up of more than one type of cell and include:
Xylem
Phloem
Also read: Short & Long Answer Questions- Tissues
(a) Parenchyma
Parenchyma cells are thin-walled, living cells that make up the basic packing tissue of all plant parts. They can be oval, spherical, or polygonal in shape, and are loosely arranged with small and large spaces in between. Their main role is to store food.
When parenchyma contains chlorophyll, it is called chlorenchyma, which is important for photosynthesis.
In aquatic plants, parenchyma cells have large air spaces that help store gases and keep the plants afloat. This special type of parenchyma is known as aerenchyma.
Parenchyma Tissue in Transverse and Longitudinal section
(b) Collenchyma
Collenchyma cells are living cells with thickened corners. The uneven thickness of their walls gives mechanical support and flexibility to the plant, allowing it to bend without breaking.
(c) Sclerenchyma
Sclerenchyma cells are usually dead, thick, and have tough walls. They have a narrow space inside. There are two types of sclerenchyma:
Fibres, which are long and spindle-shaped with pointed ends.
Sclereids, which are shorter and broader cells, sometimes called stone cells. This type of tissue provides strong support and helps plants withstand various stresses.Sclerenchyma Tissue
(d) Epidermis
The epidermis is the outer protective layer of plant parts that stops pathogens and pests from entering.
Epidermal cells are elongated and tightly packed, generally having thick outer and side walls, while the inner walls are thinner.
The thick outer walls contain a fatty substance called cutin, which makes them waterproof.
In some plants, like those in deserts, the epidermis has a thick waxy coating of cutin on its outer surface.
Root epidermal cells, which help absorb water, often have long hair-like extensions that increase the area available for absorption.
Typically, the epidermis is a single layer but has small openings called stomata that allow gas exchange. These are surrounded by two guard cells.Epidermis Water loss in the form of vapour, known as transpiration, also occurs through stomata. As plants age, the outer protective layer changes. A strip of secondary meristem in the cortex forms layers of cells called cork. Cork cells are dead, tightly packed without spaces, and contain a substance called suberin, making them impermeable to gases and water.
Epidermal cells of roots have long, hair-like structures called root hairs. These hairs help increase the surface area for better absorption of water and minerals from the soil.
On many plants, the outer surface has trichomes, which are hair-like extensions of the epidermis. These can be glandular or non-glandular and create a layer of still air on the surface, which provides insulation.
Cork is the outer protective layer found on older stems and roots. It arises from a type of lateral meristem known as cork cambium.
The cork cambium generates a secondary layer called phelloderm on the inside and cork or phellem on the outside.
Cork cells are dead and tightly packed, lacking intercellular spaces. Their walls contain a substance called suberin, which makes them resistant to gases and water.
Some cork cells have small openings called lenticels, which allow for gas exchange.
Older cork cells die and fill with substances like tannins, resins, and air.
Try yourself:
Which type of permanent tissue is responsible for providing mechanical support and flexibility to the plant?
A.Parenchyma
B.Collenchyma
C.Sclerenchyma
D.Epidermis
(ii) Complex Permanent Tissues
Complex permanent tissues consist of multiple cell types working together for a specific function.
These tissues are mainly divided into two types:
(a) Xylem
Xylem is a complex tissue that is crucial for transporting water and minerals from the soil to different parts of the plant through the roots. It includes tracheids, xylem vessels, xylem fibres, and xylem parenchyma.
Dead tubular tracheids and xylem vessels assist in moving water from roots to shoots. Living xylem parenchyma stores food.
Xylem Elements
Dead xylem fibres provide structural support. Vessels are long tubes formed by the end-to-end joining of many dead cells, with lignified walls that have pits.Working of Xylem and Phloem in plant
(b) Phloem
Phloem consists of five cell types: sieve cells, sieve tubes, companion cells, phloem fibres, and phloem parenchyma.
Sieve tubes are tubular cells with holes in their walls that transport food from the leaves to other parts of the plant. All phloem cells, except for phloem fibres, are living cells.
Phloem is the tissue responsible for transporting food that is made in leaves to other areas of the plant. It consists of five types of cells:
Sieve cells
Sieve tubes
Companion cells
Phloem fibers
Phloem parenchyma
Section of phloem
All the cells in the phloem are living, except for the phloem fibres. The main function of phloem is to transport food from the leaves to other parts of the plant, which is essential for the plant’s nutrition and growth.
Animal Tissues
Animal tissues are groups of cells that have similar structures and functions, working together to carry out specific tasks in the bodies of animals. These tissues can be divided into four main types based on their structure and function: epithelial tissue, connective tissue, muscular tissue, and nervous tissue.
Epithelial Tissues in Animals
Definition: Epithelial tissues are the protective coverings in the animal body. Functions:
Cover the majority of organs and cavities in the body.
Create barriers to separate different body systems.
Control the exchange of materials between the body and the outside environment.
Locations: Skin, lining of the mouth, lining of blood vessels, alveoli in lungs, kidney tubules.
Characteristics:
Cells are tightly packed, forming a continuous layer.
There is minimal cementing material between cells and almost no spaces.
All substances entering or leaving the body must pass through at least one layer of epithelium.
Epithelial tissue is classified by shape and function into several types, including cuboidal, columnar, ciliated, and glandular.
Try yourself:
Which type of tissue is responsible for transporting food from the leaves to other parts of the plant?
A.Xylem
B.Phloem
C.Epithelial
D.Connective
Connective Tissue
Connective tissues are identified by loosely spaced cells within a matrix that can be jelly-like, fluid, dense, or rigid, depending on the tissue’s purpose. Types of connective tissues in our body include:
Areolar tissue
Adipose tissue
Bone
Tendon
Ligament
Cartilage
Blood
Muscular Tissue
Definition: Muscular tissue is made up of long cells known as muscle fibres, which are responsible for movement.
Special Proteins: These tissues contain proteins that enable muscles to contract and relax, allowing movement.
Types of Muscular Tissue:
(i) Skeletal Muscles (Striated Muscles):
Function: Enables voluntary movements, like moving limbs.
Characteristics:
Attached to bones to facilitate body movement.
Under a microscope, these muscles display alternating light and dark bands (striations).
Cells are long, cylindrical, unbranched, and have multiple nuclei.
(ii) Smooth Muscles (Unstriated Muscles):
Function: Controls involuntary movements, such as food movement in the digestive tract and blood vessel contraction.
Locations: Found in the eye’s iris, ureters, bronchi of the lungs, and more.
Characteristics:
Cells are spindle-shaped and have a single nucleus.
These muscles do not have striations, hence called unstriated.
(iii) Cardiac Muscles:
Function: Regulates the rhythmic contraction and relaxation of the heart.
Characteristics:
Cells are cylindrical, branched, and have one nucleus.
These muscles operate involuntarily, without conscious control.
Voluntary vs. Involuntary Muscles
Voluntary Muscles: These muscles can be moved by our conscious will. They are found in our limbs and we can decide when to move them or stop.
Involuntary Muscles: These muscles work automatically without us having to think about it (for example, smooth and cardiac muscles). They are located in various parts of the body, such as the iris of the eye, ureters, and bronchi of the lungs.
Nervous Tissue
Nervous tissue plays a key role in fast communication within the body and is made up of neurons.
These cells are highly specialised to be stimulated and quickly send messages from one part of the body to another.
It includes the brain, spinal cord, and nerves.
Neurons (Nerve Cells)
Structure: A neuron has a cell body that contains the nucleus and cytoplasm, with long, thin, hair-like parts extending from it.
Axon: This is a single long extension responsible for sending signals.
Dendrites: These are many short, branched extensions that receive signals.
Length: A single neuron can be as long as a meter.
A neuron consists of a cell body, dendrites, and axons, which allow it to transmit nerve impulses.
Cells are the basic building blocks of all living organisms. They are the smallest units of life and can carry out all the necessary functions to sustain an organism. Just like how a house is made up of many rooms, a living organism is made up of many cells working together.
Discovery of Cells by Robert Hooke
In 1665, a scientist named Robert Hooke was looking at a thin slice of cork through a microscope he had designed himself.
He noticed that the cork looked like it was made up of many tiny compartments, similar to a honeycomb. Cork comes from the bark of a tree.
Hooke decided to call these tiny compartments “cells” (Latin word “cellula,” meaning a small room), and he observed dead cells in cork.
This observation was very important because it was the first time anyone had seen that living things seem to be made up of separate units.
What are Living Organisms Made Up of?
To find out, let’s Perform One Activity
Introduction:
The epidermis of an onion bulb is a single layer of cells that can be easily peeled off.
This thin layer of cells can be used to prepare a temporary mount for microscopic observation.
1. Peeling the Onion Skin: Using forceps, carefully peel off the epidermis from the concave side of the onion bulb.
2. Placing the Peel in Water: Immediately place the peeled layer in a watch glass containing water. This prevents the peel from folding or drying out.
3. Transferring the Peel to the Slide and then Preparing the Slide (i) Take a glass slide and put a drop of water on it. (ii) Transfer a small piece of the peel from the watch glass to the slide, ensuring it is flat. A thin camel hair paintbrush can help with this.
4. Adding Safranin and Staining the Peel (i) Add a drop of safranin solution to the peel. (ii) Carefully place a cover slip over the peel, using a mounting needle to avoid air bubbles.
5. Observing the Slide (i) You have now prepared a temporary mount of onion peel. (ii) Observe the slide under low power and then high power of a compound microscope to see the details of the onion cells.
6. Observation
(i) These structures look similar to each other. Together they form a big structure like an onion bulb! (ii) We find from this activity that onion bulbs of different sizes have similar small structures visible under a microscope. (iii) The cells of the onion peel will all look the same, regardless of the size of the onion they came from. (iv) These small structures that we see are the basic building units of the onion bulb. (v) These structures are called cells. (vi) Not only onions, but all organisms that we observe around us are made up of cells. (vii) However, there are also single cells that live on their own.
Scientists’ Contributions in Cell Discovery and Theory
Robert Hooke (1665). Discovered cells by observing a cork slice under a primitive microscope.
Antonie van Leeuwenhoek (1674). Using an improved microscope, he was the first to observe free-living cells in pond water.
Robert Brown (1831). Identified the nucleus within the cell.
Jan Evangelista Purkinje (1839). Coined the term ‘protoplasm’ for the cell’s fluid substance.
Matthias Schleiden (1838) and Theodor Schwann (1839). Proposed the cell theory, stating that all plants and animals are made of cells and that the cell is the basic unit of life.
Rudolf Virchow (1855). Expanded the cell theory by asserting that all cells arise from pre-existing cells.
Electron Microscope (1940). Enabled the observation and understanding of the complex structure of cells and their various organelles.
Try yourself:Who discovered the cell?
A.Robert Hooke
B.Purkinje
C.Robert Brown
D.None of these
Types of Organisms
Based on the number of cells, organisms are classified into two categories:
(a) Unicellular Organisms: These are single-celled organisms that carry out all life functions independently. Examples include Amoeba, Paramecium, Chlamydomonas, and various types of bacteria.
(b) Multicellular Organisms: These organisms are made up of many cells that work together, each taking on different roles to form various body parts. Examples include fungi, plants, and animals.
The shape and size of cells relate to their specific functions. There is a division of tasks among cells. Interestingly, most eukaryotic cells contain similar organelles, no matter their function or the type of organism they belong to.
Interesting facts and Functions of Cells in Human Body
Nerve Cell: Longest cell in the human body; carries messages across the body.
Blood Cells: RBCs (red blood cells) carry oxygen and lack nucleus (in mammals). – WBCs (white blood cells) fight infection.
Smooth Muscle Cell: Involuntary in action; helps organs like intestines to contract and relax.
Bone Cell: Stores calcium; helps build and maintain strong bones.
Fat Cell: Stores energy as fat; provides insulation and cushioning.
Ovum (Egg Cell): Largest human cell; carries mother’s DNA and supports early development.
Sperm: Smallest human cell with a tail; fertilizes the ovum to begin reproduction.
Various cells from the human body
We already know that all living organisms are made up of cells. But have you ever wondered what’s inside a cell that allows it to do so many important jobs? Let’s find out and explore the tiny parts inside a cell that help it stay alive and work properly.
What is a Cell Made Up of? What is the Structural Organisation of a Cell?
Almost every cell has three basic parts: plasma membrane, nucleus, and cytoplasm. All cell activities and interactions depend on these.
(a) Plasma Membrane or Cell Membrane
The plasma membrane is the outer layer of the cell that separates its contents from the outside environment. It allows certain materials to enter and exit the cell while blocking others, making it a selectively permeable membrane.
How does the movement of substances take place into the cell?
Types of Movement
Diffusion (For movement of gas): This is the natural movement of a substance from an area of high concentration to an area of low concentration. Gases like carbon dioxide or oxygen can pass through the cell membrane by diffusion. Other molecules require energy for transport in and out of the cell.
Osmosis (For Movement of Water): Osmosis is the diffusion of water across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.
Do you know: Osmosis is special case of diffusion
The movement of water across the plasma membrane is also affected by the amount of substance dissolved in water. Thus, osmosis is the net diffusion of water across a selectively permeable membrane toward a higher solute concentration.
What happens if we place an animal or plant cell in a sugar or salt solution? One of three outcomes may occur:
Hypotonic Solution: If the surrounding solution has a higher concentration of water than the cell, the cell will absorb water through osmosis. This is known as a hypotonic solution, leading to more water entering the cell than leaving it.
Isotonic Solution: If the surrounding solution has the same concentration of water as the cell, there will be no net movement of water across the cell membrane. This is an isotonic solution, where water moves in and out at equal rates.
Hypertonic Solution: If the surrounding solution has a lower concentration of water than the cell, the cell will lose water through osmosis. This is a hypertonic solution, causing the cell to shrink as water exits.
Examples and facts of Diffusion and Osmosis
1. A de-shelled egg placed in pure water swells because water enters the egg by osmosis. The same egg placed in concentrated salt solution shrinks as water moves out of the egg.
2. Dried raisins or apricots swell in plain water as they gain water by osmosis. In concentrated sugar/salt solution, they shrink due to loss of water.
3. Osmosis is important in plant roots and unicellular freshwater organisms for absorbing water.
4. Diffusion is important for exchange of gases and water in and out of the cell.
5. The plasma membrane, made of lipids and proteins, controls the movement of substances in and out of the cell, and its flexibility allows the cell to engulf food by endocytosis, as seen in Amoeba.
(b) Cell Wall
In addition to the plasma membrane, plant cells have a tough outer layer called the cell wall. This wall is located outside the plasma membrane and is mainly made of cellulose, a complex substance that gives plants their structural strength.
When a living plant cell loses water through osmosis there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is known as plasmolysis.
Function of Cell Wall
Cell walls allow plant, fungal, and bacterial cells to endure very dilute (hypotonic) external solutions without bursting. In such solutions, cells absorb water through osmosis, causing them to swell and exert pressure against the cell wall. The wall then pushes back, creating equal pressure.
Due to their walls, plant cells can handle much larger changes in their environment compared to animal cells.
Plasmolysis: This occurs when a living plant cell loses water by osmosis, resulting in the cell contents shrinking away from the cell wall.
Try yourself:
What is the function of the plasma membrane in a cell?
A.Allows the entry and exit of some materials
B.Prevents the movement of all materials
C.Only allows the entry of water
D.Only allows the exit of water
(c) Nucleus
The nucleus has a double layer called the nuclear membrane.
The nuclear membrane has pores that allow materials to move between the nucleus and the cytoplasm.
The nucleus contains chromosomes, which are visible as rod-shaped structures only when the cell is about to divide.
Chromosomes hold the information needed to pass traits from parents to their children in the form of DNA (Deoxyribonucleic Acid).
Chromosomes are made up of DNA and protein.
DNA molecules carry the information required for building and organising cells.
Functional parts of DNA are known as genes.
In a non-dividing cell, DNA exists as chromatin material, which looks like a tangled mass of thread-like structures.
When the cell is ready to divide, the chromatin organises into chromosomes.
The nucleus is vital for cell reproduction, which is when a single cell divides to form two new cells.
The nucleus also plays an important role, along with the environment, in guiding how the cell develops and what it looks like when it matures.
It directs the chemical activities of the cell.
Nucleus of a Eukaryotic cell
Prokaryotic and Eukaryotic Cells
Prokaryotic Cells
Prokaryotes are organisms with cells that do not have a nuclear membrane.
Typically, prokaryotic cells are small, ranging from 1 to 10 µm in size.
They contain a nucleoid, which is an area with nucleic acids but lacks a surrounding membrane.
Prokaryotic cells do not have membrane-bound organelles.
They possess a single chromosome made of nucleic acid.
Also read: Short and Long Answer Questions- The Fundamental Unit Of Life
Eukaryotic Cells
Eukaryotes are organisms with cells that have a nuclear membrane.
Eukaryotic cells are generally larger, measuring from 5 to 100 µm.
They have a defined nuclear membrane and contain multiple chromosomes.
Eukaryotic cells include complex organelles that perform specific functions.
Q: Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.
Cytoplasm
The cytoplasm is the fluid inside the plasma membrane.
It contains various specialised cell organelles, each with specific roles.
The cytoplasm facilitates the exchange of materials between organelles.
The cytoplasm is where certain metabolic pathways, such as glycolysis, take place.
Try yourself:What do chromosomes carry information for?
A.Creating energy
B.Storing nutrients
C.Cell division
D.Passing traits
Cell Organelles
Organelles are specialised structures that perform different tasks within cells. The term literally means “little organs.” Just as organs like the heart, liver, stomach, and kidneys have specific functions to keep an organism alive, organelles have specific roles to support the life of a cell. Membrane-bound organelles are a feature of eukaryotic cells and absent in prokaryotes.
1. Endoplasmic Reticulum (ER)
The endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets that resemble long tubules or round bags called vesicles. The structure of the ER membrane is similar to that of the plasma membrane, made up of lipids and proteins. There are two types of ER: rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER).
Although the ER can look different in various cells, it consistently forms a network system.
Endoplasmic Reticulum
Types of Endoplasmic Reticulum
Functions of Rough and Smooth Endoplasmic Reticulum
The RER contains ribosomes, which are the sites for protein production. These proteins are transported to different parts of the cell as needed.
The SER aids in creating lipids, which are essential for cell function.
Some proteins and lipids serve as enzymes and hormones.
The ER acts as channels, transporting materials (especially proteins) within the cytoplasm or between the cytoplasm and the nucleus.
The endoplasmic reticulum provides a cellular framework in the cytoplasm, supporting specific cell activities.
In vertebrate liver cells, the SER is vital for detoxifying various poisons and drugs.
2. Golgi Apparatus
The Golgi apparatus is made up of a system of membrane-bound vesicles that are arranged in stacks known as cisterns. These membranes often connect with the membranes of the ER, forming part of a complex cellular membrane system. Golgi Apparatus
Function of the Golgi Body
The material synthesised near the ER is packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus.
Its functions include the storage, modification and packaging of products in vesicles. In some cases, complex sugars may be made from simple sugars in the Golgi apparatus.
The Golgi apparatus is also involved in the formation of lysosomes.
3. Lysosomes
Lysosomes act as the waste disposal system of the cell. They have a membrane-bound structure and contain digestive enzymes made by the rough endoplasmic reticulum (RER).
Lysosome
Functions of Lysosomes
Lysosomes break down foreign materials entering the cell, like bacteria or food, and also old organelles into smaller pieces.
They contain powerful digestive enzymes that turn complex substances into simpler ones.
They break down old organelles.
If the cell is damaged, lysosomes may burst and the enzymes can digest their own cell. Hence, lysosomes are sometimes called the ‘suicide bags‘ of a cell.
4. Mitochondria
Mitochondria are known as the powerhouse of the cell.
Mitochondria
Structure of Mitochondria
Mitochondria have two membrane coverings.
The outer membrane is very porous, while the inner membrane has deep folds. These folds create a large surface area for ATP-generating chemical reactions.
Functions of Mitochondria
Mitochondria release energy needed for various chemical processes required for life in the form of ATP (Adenosine triphosphate) molecules. ATP is recognised as the energy currency of the cell.
The body uses energy stored in ATP to create new chemical compounds and for mechanical work.
Mitochondria are unique as they have their own DNA and ribosomes, allowing them to produce some of their own proteins.
Try yourself:
What is the function of cell organelles?
A.Store energy
B.Help cells function
C.Create food
D.Protect from diseases
Also read: Short and Long Answer Questions- The Fundamental Unit Of Life
5. Plastids
Plastids are found only in plant cells.
There are two types of plastids:
Chromoplasts (coloured plastids).
Leucoplasts (colourless plastids) mainly store materials like starch, oils, and protein granules.
Plastid
Structure of Plastids
The plastids’ internal structure includes multiple layers of membranes surrounded by a substance known as the stroma.
Plastids also have their own DNA and ribosomes, like mitochondria, and are similar to mitochondria in their structure
Function of Plastids
Chromoplasts containing the pigment chlorophyll are known as chloroplasts. Chloroplasts are important for photosynthesis in plants.
Leucoplasts are primarily organelles in which materials such as starch, oils and protein granules are stored.
6. Vacuoles
Vacuoles are storage sacs that hold solid or liquid materials. In animal cells, they are typically small, while in plant cells, they can be quite large. The central vacuole in some plant cells may take up 50-90% of the cell’s volume.
In plant cells, vacuoles are filled with cell sap, which helps the cell maintain its shape and firmness. Vacuoles store many important substances for the plant cell, such as: Amino acids, Sugars, Various organic acids andSome proteins.
In single-celled organisms like Amoeba, the food vacuole holds the food that the Amoeba has eaten. Some unicellular organisms have special vacuoles that are important for: (i) removing excess water from the cell and (ii) getting rid of certain wastes.
Cell Division
The process of creating new cells is known as cell division. New cells are produced in living organisms to:
grow
replace old, dead, and damaged cells
form gametes needed for reproduction
There are two main types of cell division: mitosis and meiosis.
Mitosis or Mitotic Cell Division
Mitosis is the process through which most cells divide for growth. In this process, each original cell, known as the mother cell, splits to create two genetically identical daughter cells (Fig. 5.7). The daughter cells have the same number of chromosomes as the mother cell. This process is essential for the growth and repair of tissues in organisms.
MITOSIS
Meiosis or Meiotic Cell Division
In animals and plants, certain cells in reproductive organs or tissues divide to create gametes, which will develop into offspring after fertilisation. This division occurs through a different method called meiosis, which involves two successive divisions. When a cell undergoes meiosis, it produces four new cells instead of just two (Fig. 5.8). These new cells contain only half the number of chromosomes compared to the mother cells.
MEIOSIS
Difference between an Animal Cell and a Plant Cell
The structure of an atom consists of protons, neutrons, and electrons. Protons and neutrons each have a mass of one unit, while the mass of an electron is so small that it is often ignored. These fundamental components determine the mass and charge of the atom.
Atomic structure is about how these subatomic particles—protons, neutrons, and electrons—are arranged within an atom, which affects its composition and behaviour.
Structure of Atom
John Dalton believed that the atom cannot be divided.
In 1886, E. Goldstein found new radiations in a gas discharge tube, naming them canal rays. These rays carry a positive charge.
In 1897, J.J. Thomson discovered the electron, a subatomic particle with a negative charge.
The neutron was discovered by Chadwick and has no charge.
Let’s Revise: Why is the mass of the electron usually ignored?
Ans: Because it is approximately 1/1836 the mass of a proton, making it negligible.
Thomson’s Model of an Atom
Thomson’s Model of the Atom, referred to as the plum pudding model, suggested that the atom is made up of a positively charged sphere with negatively charged electrons scattered throughout it, akin to currants in a Christmas pudding. Another way to picture it is like a watermelon, where the positive charge is spread out like the red fruit, and the electrons are like seeds embedded within.
Electrons are embedded in a positively charged sphere; overall atom is neutral.
The negative and positive charges are balanced, leading to an atom that is overall electrically neutral.
Plum Pudding Model
Try yourself:
What does Thomson’s Model of the Atom compare to a watermelon?
A.The color
B.The rind
C.The juice
D.The seeds
Rutherford’s Model of an Atom
Rutherford’s Model of the Atom brought forth the concept of a small, dense nucleus at the centre of the atom, with electrons moving around it, which greatly changed our understanding of atomic structure.
Rutherford’s Experiment
α-particles are He2+ nuclei (mass ≈ 4 u, charge +2e) emitted at high speeds, hence have high kinetic energy.
Most of the atom’s interior is empty, as many α-particles went through the gold foil without deflecting.
A few particles were deflected, suggesting that the positive charge of the atom takes up very little space.
A tiny number of α-particles were deflected back by 180°, showing that the positive charge and mass of the gold atom are concentrated in a very small area.
Conclusions made by Rutherford
He calculated that the nucleus’s radius is about 100,000 times smaller than that of the atom.
The Nuclear Model of an Atom proposed by Rutherford includes:
A positively charged centre called the nucleus, where nearly all the mass of the atom is found.
The electrons orbit the nucleus in circular paths.
The nucleus is very small compared to the atom’s overall size.
Rutherford’s Nuclear Model of Atom
Drawbacks of Rutherford’s Model of the Atom
The orbiting electron in a circular path should not be stable. Any particle in such an orbit would experience acceleration. During this acceleration, charged particles would lose energy by radiating it. Therefore, the electron would lose energy and eventually spiral into the nucleus. If this were true, atoms would be highly unstable, which contradicts the fact that matter exists in a stable form.
Try yourself:Rutherford’s ‘alpha (α) particles scattering experiment’ resulted in the discovery of
A.electron
B.proton
C.nucleus in the atom
D.atomic mass
Bohr’s Model of Atom
Bohr’s Model of the Atom changed how we understand atomic structure by introducing the idea that electrons move around the nucleus in specific energy levels. This model helps explain why atoms are stable and how they produce spectral lines.
Historical Context of Niels Bohr
Niels Bohr (1885-1962) was born in Copenhagen on 7 October 1885. He became a professor of physics at Copenhagen University in 1916 and won the Nobel Prize for his contributions to atomic structure in 1922. Some of his important writings include:
The Theory of Spectra and Atomic Constitution
Atomic Theory
The Description of Nature
Also read: NCERT Solutions: Structure of the Atom
Postulates of Niels Bohr
Only certain specific orbits, called discrete orbits, are allowed for electrons inside the atom.
Electrons do not emit energy while they are moving in these discrete orbits.
These orbits or shells are referred to as energy levels. Energy levels in an atom are illustrated in Fig. 4.3.
Drawbacks of Bohr’s Model of Atom
Works for hydrogen but fails for multi-electron atoms.
Cannot explain the splitting of spectral lines (fine structure; effects in magnetic/electric fields).
Does not account for line intensities in spectra.
Assumes fixed circular orbits; later quantum model uses orbitals (no fixed paths).
Neutrons
In 1932, J. Chadwick discovered a subatomic particle with no charge, which has a mass almost equal to that of a proton. This particle is called a neutron. Neutrons are found in the nucleus of all atoms, excepthydrogen-1 (protium). Deuterium and tritium contain neutrons. Generally, a neutron is denoted as ‘n’. The mass of an atom is the total of the masses of the protons and neutrons in the nucleus.
Bohr’s Model
Let’s Revise: How is a hydrogen atom different from atoms of all other elements?
Ans: All atoms consist of three subatomic particles: electrons, protons, and neutrons. The hydrogen atom contains only one electron and one proton, and it has no neutrons, making it unique among all elements.
Distribution of Electrons in Different Orbits
The way electrons are arranged in various orbits, or energy levels, defines an atom’s electron configuration.
Rules
The maximum number of electrons that can fit in a shell is determined by the formula 2n², where ‘n’ represents the orbit number or energy level index (1, 2, 3, …).
The outermost orbit can hold a maximum of 8 electrons.
Fill shells step-wise (K → L → M …); outermost shell holds at most 8 electrons even if 2n2 allows more.
Thus, the maximum number of electrons in various shells is as follows:
First orbit or K-shell can hold = 2 electrons
Second orbit or L-shell can hold = 8 electrons
Third orbit or M-shell can hold = 18 electrons
Fourth orbit or N-shell can hold = 32 electrons
The atomic structure of the first eighteen elements is illustrated in a diagram.
The electrons in the outermost shell of an atom are called valence electrons. The number of valence electrons is essential in defining the chemical properties of the element.
Valency
Atomic structure of the first eighteen elements
An atom of each element has a definite combining capacity, called its valency.
The number of bonds that an atom can form in a compound is shown by its valency.
Valence electrons are the electrons in the outermost orbit of the atom.
Let’s Revise
Q: How is the maximum number of electrons in a shell calculated?
Ans: By the formula 2n², where n is the orbit number.
Q: Why are valence electrons important?
Ans: They determine the chemical properties and bonding behaviour of the element.
Also read: NCERT Solutions: Structure of the Atom
Atomic Number & Mass Number
The atomic number indicates the number of protons in an atom’s nucleus, represented by ‘Z’.
The mass number is the total count of protons and neutrons, giving information about the atom’s identity and mass.
The total number of protons in an atom’s nucleus is its atomic number, symbolised as ‘Z’.
The mass number of an atom is the sum of its protons and neutrons, represented by the letter ‘A’.
An element is represented as AXZ, where Z is the atomic number (equal to the number of protons), A is the mass number, and X is the element’s symbol. The mass number (A) can be calculated as: Mass number (A) = Number of protons (Z) + Number of neutrons.
Let’s Revise: What is the mass number?
Ans: The mass number of an element is the total of the number of protons and neutrons in the atom of that element.
Mass Number A = Number of protons + Number of neutrons.
For hydrogen, Z = 1, as there is only one proton in a hydrogen atom’s nucleus. Therefore, the mass number of H is 1.
Mass Number A refers to the total count of nucleons (protons and neutrons) in the nucleus.
Isotopes
Atoms of the same element with the same atomic number but different mass numbers are called isotopes. For example, hydrogen has three isotopes: protium (H), deuterium (²H or D), and tritium (³H or T).
Chemical properties → same
Physical properties → differentIsotopes of HydrogenApplications of Isotopes: (a) An isotope of Uranium is used as fuel in nuclear reactors. (b) An isotope of Cobalt is used in the treatment of cancer. (c) An isotope of Iodine is used in the treatment of goitre.
Try yourself:The number of electrons in a neutral atom of an element X is 15, and the number of neutrons is 16. Which of the following is the correct representation of the element?
A. 31X15
B. 31X16
C.16X15
D. 15X16
Isobars
Atoms of different elements that have the same mass number but different atomic numbers are called isobars. For example, Argon-40 (₁₈Ar⁴⁰) and calcium-40 (₂₀Ca⁴⁰) are isobars. Examples of Isobars
Let’s Revise
Q: What are General Features of Isotopes?
Ans:The general features of isotopes are:
Isotopes of an element have the same atomic number, meaning they have the same number of protons and electrons.
They have different mass numbers, resulting from a different number of neutrons.
The chemical properties of isotopes are similar, but their physical properties differ.
Different masses lead to variations in physical properties like melting point, boiling point, and density.
Q: What are Isotones?
Ans. Some atoms of different elements have different atomic numbers and different mass numbers but they have a same number of neutrons. These atoms are known as isotones.
Example:14C6 and 16O8.
Both C and O have the same number of neutrons i.e. 8.
Atoms and molecules are the fundamental building blocks of matter. A clear understanding of atoms and molecules explains why substances combine in particular ways, why physical and chemical properties differ from one substance to another, and how new substances are formed in chemical reactions.
Maharishi Kanad and Pakudha Katyayama in ancient India proposed that matter can be divided into smaller indivisible particles called Parmanu.
Democritus and Leucippus in ancient Greece proposed a similar idea: matter is made of indivisible particles called atoms.
These early ideas were philosophical and lacked experimental proof until modern chemistry developed in the 18th century.
In the late 18th century, Antoine L. Lavoisier established quantitative methods in chemistry and laid foundations for modern chemical science by formulating laws about chemical combinations.
Lavoisier and Joseph L. Proust performed careful experiments that led to two important laws: the Law of Conservation of Mass and the Law of Constant Proportions (also called the Law of Definite Proportions).
These laws guided later work and helped John Dalton formulate his atomic theory that explained why these laws hold true for chemical reactions.
Try yourself:
Who proposed the idea that matter can be divided into smaller particles called Parmanu?
A.Maharishi Kanad
B.Democritus
C.Antoine L. Lavoisier
D.Joseph L. Proust
Laws of Chemical Combination
Two fundamental laws describe how substances combine in chemical reactions: the Law of Conservation of Mass and the Law of Constant Proportions. These laws provide the experimental basis for the atomic view of matter.
1. Law of Conservation of Mass
The Law of Conservation of Mass states that mass can neither be created nor destroyed in a chemical reaction. The total mass of reactants equals the total mass of products.
Example of Law of conservation of Mass
Careful experiments – for example, mixing chemical solutions in closed containers and measuring mass before and after reaction – show that the measured total mass remains unchanged, supporting this law.
Try yourself:
According to the Law of Conservation of Mass, what happens to the mass during a chemical reaction?
A.The mass increases.
B.The mass decreases.
C.The mass remains constant.
D.The mass is converted into energy.
2. Law of Constant Proportion
The Law of Constant Proportion (Law of Definite Proportions) states that a chemical compound always contains the same elements in the same fixed proportion by mass, irrespective of its source.
Example of Law of Constant Proportion
For example, pure water always contains hydrogen and oxygen in the mass ratio 1 : 8. This proportion is the same whether the water comes from a river, a well, or rain.
John Dalton’s Atomic Theory
To explain these laws, John Dalton proposed an atomic theory which gave an experimental and conceptual basis for atoms and compounds.
John Dalton
Postulates of Dalton’s Atomic Theory
All matter is made of extremely small particles called atoms.
Atoms are indivisible by chemical means and remain unchanged in chemical reactions.
Atoms of the same element are identical in mass and properties.
Atoms of different elements have different masses and properties.
Atoms combine in simple whole-number ratios to form compounds.
The relative number and types of atoms in a given compound are constant (fixed composition).
Background on John Dalton
John Dalton was born in 1766. His atomic hypothesis explained the Law of Conservation of Mass and the Law of Definite Proportions quantitatively and conceptually.
What is an Atom?
An atom is the smallest particle of an element that retains the chemical properties of that element and cannot be broken down by chemical means.
Atoms are extremely small; a very large number of atoms are required to form visible matter.
A layer only a few million atoms thick may be comparable in thickness to a sheet of paper.
Atomic Radius
The atomic radius is a measure of the size of an atom, typically expressed in nanometres (nm), where 1 nm = 10-9 m.
Try yourself:
Which statement best describes the Law of Constant Proportion?
A.It states that in a chemical substance, elements are always present in definite proportions by volume.
B.It states that in a chemical substance, elements are always present in definite proportions by mass.
C.It states that in a chemical substance, elements are always present in indefinite proportions by mass.
D.It states that in a chemical substance, elements can be present in any proportions by mass.
Modern Symbols of Elements
Element symbols evolved from early pictorial symbols to the simple one- or two-letter symbols used today. The International Union of Pure and Applied Chemistry (IUPAC) standardises these symbols.
Historical background: John Dalton first used symbols to represent atoms. Later, Berzelius proposed using one or two letters derived from the element name to represent elements.
Origin of element names: Some names come from places (e.g., copper from Cyprus) or from colours and other properties.
Modern symbols: Most element symbols are derived from their English names; the first letter is capitalised and a second letter, if used, is lowercase.
First letter + another letter: Examples include Chlorine: Cl, Zinc: Zn.
Names from other languages: Some symbols come from Latin, Greek or other languages: Iron: Fe (ferrum), Sodium: Na (natrium), Potassium: K (kalium).
Symbols for Some Elements
Try yourself:
Which scientist pioneered the use of symbols for elements?
A.Berzelius
B.Dalton
C.IUPAC
D.None of the above
Atomic Mass
Atomic mass of an atom is the mass of that atom expressed relative to a standard. The standard used internationally is defined as 1/12 of the mass of a carbon-12 atom. The unit for atomic mass is the unified atomic mass unit (symbol u, also called amu).
Atomic mass is the combined mass of protons, neutrons and electrons in an atom; in practice the electron mass is very small relative to protons and neutrons and often neglected in simple calculations.
Atomic masses reported on the periodic table are average values that reflect the natural isotopic composition of the element.
Atomic mass of some elements
How Do Atoms Exist?
Many atoms do not exist freely under normal conditions; they combine to form molecules or form ions that aggregate into ionic structures.
Visible matter is composed of huge numbers of molecules or ionic units assembled together.
What is a Molecule?
A molecule is the smallest particle of an element or compound that can exist independently and retain the chemical properties of that substance.
Molecules of Elements
Monoatomic molecules: Some elements exist as single atoms (monoatomic) in their natural gaseous state, e.g., Helium (He), Argon (Ar).
Diatomic molecules: Several non-metals exist as molecules of two atoms, e.g., Hydrogen (H2), Oxygen (O2), Nitrogen (N2), Chlorine (Cl2).
Polyatomic molecules: Some elements form molecules with more than two atoms, e.g., Phosphorus (P4), Sulphur (S8).
Try yourself:What is the atomic mass of an atom?
A. The total mass of the neutrons and protons in an atom.
B.The mass of a carbon-12 atom in its ground state.
C.The average mass of a group of atoms.
D.The mass of an atomic particle.
Atomicity
Atomicity is the number of atoms present in one molecule of an element.
Atomicity of some non-metals
Molecules of Compounds
When atoms of different elements combine, they form molecules of compounds. These molecules have fixed compositions and properties different from their constituent elements.
What is an Ion?
An ion is an atom or a group of atoms that carries an electric charge due to loss or gain of electrons.
A positively charged ion is called a cation; a negatively charged ion is called an anion.
Compounds formed from metals and non-metals often contain ions; such compounds are called ionic compounds.
Polyatomic ions are groups of atoms bonded together that carry a net charge, for example, NO3–, SO42-, OH–.
Writing Chemical Formulae
The chemical formula of a compound shows which elements are present and the number of atoms of each element in the smallest unit of that compound.
To write formulae, you must know element symbols and the valencies (combining capacities) or ionic charges of the atoms/ions involved.
Valency indicates how many electrons an atom gains, loses or shares when it forms a compound.
Think of valency as the number of bonds an atom typically forms: it is the atom’s “combining power”.
Rules for Formula Writing
The total positive charge and total negative charge in a neutral compound must balance.
When writing formulae for compounds of a metal and a non-metal, write the metal first and the non-metal second (e.g., CaO, NaCl).
Use the simplest whole-number ratio of atoms or ions that balances charges.
When polyatomic ions are present in more than one number, enclose the polyatomic ion in brackets and write the number outside the brackets, e.g., Mg(OH)2.
Practice with examples to become familiar with common valencies and formulas.
Try yourself:What is the atomicity of a molecule?
A.The number of atoms in a molecule
B.The number of ions in a molecule
C.The number of elements in a molecule
D.The number of protons in a molecule
Also read: Short and Long Answer Questions: Atoms and Molecules
Formulae of Simple Compounds
Binary compounds (formed by two elements) can be written by criss-crossing valencies or balancing charges of ions.
Example:
Carbon tetrachloride, CCl4: Carbon (valency 4) combines with chlorine (valency 1) to give the formula CCl4.
Magnesium chloride, MgCl2: Magnesium (valency 2) combines with chlorine (valency 1) to give MgCl2.
Molecular Mass
The molecular mass (relative molecular mass) of a molecule is the sum of the atomic masses of all atoms present in the molecule. It is expressed in atomic mass units (u).
Example 1:
(a) Calculate the relative molecular mass of water (H2O).
(b) Calculate the molecular mass of HNO3.
Solution:
(a)
Atomic mass of hydrogen = 1 u.
Atomic mass of oxygen = 16 u.
The molecular mass of H2O = 2 × (atomic mass of H) + 1 × (atomic mass of O).
The molecular mass of H2O = 2 × 1 + 16 = 18 u.
(b)
Atomic mass of hydrogen = 1 u.
Atomic mass of nitrogen = 14 u.
Atomic mass of oxygen = 16 u.
The molecular mass of HNO3 = 1 × (atomic mass of H) + 1 × (atomic mass of N) + 3 × (atomic mass of O).
The molecular mass of HNO3 = 1 + 14 + 3 × 16 = 63 u.
Try yourself:What is the chemical formula for magnesium chloride?
A.MgC2
B.ZnCl2
C.MgCl2
D.Mg
Formula Unit Mass
Formula unit mass is the sum of the atomic masses of the atoms present in the formula unit of an ionic compound. It is calculated the same way as molecular mass but applied to ionic formula units.
Example 2: Calculate the formula unit mass of CaCl2.
Solution:
The atomic mass of Ca = 40 u.
The atomic mass of Cl = 35.5 u.
The formula unit mass of CaCl2 = atomic mass of Ca + 2 × atomic mass of Cl.
The formula unit mass of CaCl2 = 40 + 2 × 35.5 = 40 + 71 = 111 u.
Have you ever wondered if the water you drink, the air you breathe, or even the food you eat is completely pure? The chapter delves into the fascinating world of matter, where we explore how everything around us, from a simple sugar cube to the air we inhale, is made up of pure substances or mixtures. You’ll discover how mixtures can be separated into their components, and how pure substances are the building blocks of everything we see and use!
What Is a Mixture?
Mixtures are constituted by more than one kind of pure form of matter, known as a substance. For example, sea water, minerals, soil etc., are all mixtures.
When we say that something is pure, it means that all the constituent particles of that substance are the same in their chemical nature. A pure substance always consists of a single type of particle.
When we look around, we can see that most of the matter around us exist as mixtures of two or more pure components.
Examples of Mixtures
Dissolved sodium chloride can be separated from water by the physical process of evaporation but sodium chloride cannot be separated into sodium and chlorine by physical means.
Types of mixtures
Depending upon the nature of components that form a mixture, we can have different types of mixtures.
Homogeneous mixtures: Mixtures which have a uniform composition throughout, are called homogeneous mixtures. For example, salt in water and sugar in water.
Heterogeneous mixtures: Mixtures which contain physically distinct parts and have non-uniform composition are called heterogeneous mixtures. For example, mixture of sodium chloride and iron filings, salt and sulphur.
Activity: Perform an activity to differentiate between solution, suspension and colloidal solution.
Procedure:
Distribute the following samples to four groups A, B, C and D of a class.
A few crystals of copper sulphate to group A.
One spatula is full of copper sulphate to group B.
Chalk powder to group C.
A few drops of milk or ink to group D.
Ask each group to add the sample to water and stir using a glass rod.
Direct a beam of light from a torch through the beakers.
Leave the mixture undisturbed for a few minutes.
Filter the mixtures
Solution, Suspension and Colloidal Solution
Observations:
We observe that groups A and B get a clear solution of copper sulphate although with different colour density.
Group C get a suspension of chalk, which on filtration gives a residue of chalk on the filter paper and clear filtrate containing water.
Group D get a colloidal solution of milk. The solution in this case is not transparent. But no suspension is obtained here and on filtration, no residue is obtained on the filter paper.
Conclusion:
Group A and B created homogeneous mixtures with uniform composition, while Groups C and D made heterogeneous mixtures with distinct parts.
This activity illustrates the difference between homogeneous and heterogeneous mixtures based on composition and appearance.
Try yourself:
What is a homogeneous mixture?
A.A mixture that contains physically distinct parts and has a non-uniform composition.
B.A mixture that has a uniform composition throughout.
C.A mixture that can be separated into its individual components by physical means.
D.A mixture that consists of a single type of particle.
What is a Solution?
A solution is a homogeneous mixture of two or more substances. Lemonade and soda water are example of solutions.
A solution is not necessarily a liquid containing a solid, liquid or gas dissolved in it. Solid solution (alloys) and gaseous solution are also possible.
Alloys
Alloys are homogeneous mixtures of metals and cannot be separated into their components by physical methods. For example, brass is a mixture of approximately 30% zinc and 70% copper.
Solvent and solute
Solvent and solute are the components of the solution.
Solvent: The component that dissolves the other component in it is the solvent.
Solute: The component that is dissolved in the solvent is called solute.
For example, Tincture of iodine is a solution of iodine in alcohol. Aerated drinks like soda water are solutions of carbon dioxide as solute and water as solvent. Air is a mixture of a gas in a gas. The two major components of air are nitrogen (78%) and oxygen (21%).
Note: Generally solute is present in smaller quantity and solvent is present in greater quantity. For example, we have a solution of sugar in water in which case sugar is solute and water is the solvent.
Properties of a solution
A solution is a homogeneous mixture.
Particles of a solution are smaller than 1 nm (10-9metre) in diameter. Therefore, they cannot be seen by naked eye.
Because of small size, they do not scatter light.
Solute particles cannot be separated from the mixture by filtration.
Concentration of the solution
Concentration of a solution is the amount of solute present in a given amount (mass or volume) of solution.
A concentrated solution contains a large concentration of the solute in the solvent while a dilute solution contains a small concentration of the solute in the solvent.
Mass by mass percentage of a solution
Mass by volume percentage of a solution
Saturated solution
At any particular temperature, a solution that has dissolved as much solute as it is capable of dissolving, is called saturated solution.
No more solute can be dissolved in the saturated solution at a given temperature.
Solubility: The amount of solute present in a saturated solution at a given temperature is called its solubility
Unsaturated solution
If the amount of solute contained in a solution is less than saturation level, it is called unsaturated solution.
Different substances in a given solvent have different solubilities at the same temperature.
What is a Suspension?
A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of medium.
Particles of a suspension are visible to the naked eye.
For example, chalk powder in water.
Properties of a suspension
Suspension is a heterogeneous mixture.
Particles of suspension can be seen with a naked eye.
Particles of a suspension scatter light passing through it and make its path visible.
Solute particles in a suspension settle down after some time when kept undisturbed.
Components of a suspension can be separated by the process of filtration.
What is a Colloidal solution?
A colloidal solution is a heterogeneous mixture in which the solute particles do not settle down but remain suspended.
Here the particle size of the solute is between 1 nm to 100 nm.
Colloidal particles cannot be seen with a naked eye but they scatter light thus making the path of light visible.
For example, milk and starch solution.
Solution of Copper Sulphate does not show Tyndall Effect, Mixture of Water and Milk shows Tyndall Effect
Properties of colloidal solutions
A colloidal solution is a heterogeneous mixture.
The particles of a colloid cannot be seen with a naked eye.
Colloidal particles scatter light.
Colloidal particles do not settle down when left undisturbed.
Colloidal particles cannot be separated from the mixture by the process of filtration.
Dispersed phase and dispersion medium
These are the components of a colloidal solution.
The solute-like component in a colloidal solution are dispersed phase and the solvent like component in a colloidal solution is dispersed medium.
Some common examples of colloids
Physical and Chemical changes
A change which occurs without a change in composition and chemical nature of the substance is called physical change.
Here a change only in physical properties of the substance takes place.
Properties like colour, hardness, rigidity, fluidity, density, melting point and boiling point are known as physical properties.
Melting of ice or boiling of water is a physical change because ice, water and water vapours are chemically the same substance i.e., H20.
A change of materials into another, new materials with different properties and one or more than one new substances are formed is called chemical change.
Burning is a chemical change.
During this process, one substance reacts with another substance to undergo a change in chemical composition.
During burning of candle, actually both physical and chemical changes take place.
The physical change involves the melting of wax and the chemical change involves the burning of wax into carbon dioxide and water.
Try yourself:
What is a solution?
A.A heterogeneous mixture of two or more substances.
B.A homogeneous mixture of two or more substances.
C.A mixture of metals that cannot be separated by physical methods.
D.A mixture in which solute particles do not dissolve but remain suspended.
What are the Types of Pure Substances?
On the basis of their chemical composition, substances can be classified either as elements or compounds.
Elements
Lavoisier, a French chemist defined an element as the basic form of matter that cannot be broken down into simpler substances by chemical reactions.
Elements can be divided into the following main threetypes of substances:
Metals.
Non-metals.
Metalloids.
Metals show the following properties
They have a Lustre.
They have silvery-grey or golden-yellow colour.
They conduct heat and electricity.
They are ductile that means they can be drawn into thin wires.
They are malleable. That means they can be beaten into thin sheets.
They are sonorous i.e., they make a ringing sound when hit.
Examples of metals are gold, silver, copper, iron, sodium, etc.
Non-metals show the following properties
They display a variety of colours.
They are poor conductors of heat and electricity.
They are not lustrous, sonorous or malleable.
Examples of non-metals are oxygen, iodine, carbon, etc.
Some elements have intermediate properties between those of metals and non-metals.
They are called metalloids.
Examples of metalloids are boron, silicon and germanium.
Some facts about elements
The number of elements known at present is more than 100. Ninety two elements are naturally occurring and the rest are man-made.
Majority of the elements are solids.
Eleven elements are in gaseous state at room temperature.
Two elements are liquid at room temperature – mercury and bromine.
Elements gallium and cesium become liquid at a temperature slightly above room temperature (303 K).
Compounds
A compound is a substance composed of two or more elements chemically combined with one another in a fixed proportion.
Activity – Exploring the Properties of Iron and Sulphur Mixture.
Materials required: Crushed iron filings, sulphur, china dish, burner.
Procedure:
Divide the class into two groups.
Provide each group with 5 g of iron filings and 3 g of sulphur powder in a china dish.
Group I:
Mix and crush iron filings and sulphur powder together.
Group II:
Mix and crush iron filings and sulphur powder together.
Heat the mixture strongly until it becomes red hot.
Remove from flame and let the mixture cool down.
Both Groups:
Check for magnetism in the material obtained by bringing a magnet near it.
Compare the texture and color of the material obtained by both groups.
Add carbon disulphide to one part of the material obtained, stir well, and filter.
Add dilute sulphuric acid or dilute hydrochloric acid to another part of the material obtained. (Note: Teacher supervision is necessary for this activity).
Perform all the above steps with iron and sulphur separately.
Observation: Upon heating, iron and sulfur react chemically to form a compound. This compound has different properties from the original elements, indicating a chemical change. The mixture of iron and sulfur before heating shows the individual properties of both substances, but once heated, a new substance with distinct properties is created.
Conclusion
When iron and sulfur are mixed and heated:
Group I demonstrates a physical change, resulting in a mixture with similar properties to the individual substances (iron and sulfur).
Group II exhibits a chemical change, where iron and sulfur react to form a compound with different properties.
This experiment highlights the differences between physical and chemical changes, as well as the concepts of mixtures and compounds in chemistry.
Mixture
If we simply mix iron filings with powdered sulphur and grind them together (no heating), we. obtain a mixture.
Comparison between mixtures and compounds
Table: Mixtures and Compounds
We can summarise the physical and chemical nature of matter as under:
When we observe our surroundings, we notice a vast array of objects, each differing in shape, size, and texture. Despite these differences, all these objects share a fundamental characteristic: they are made up of matter. But what exactly is the matter?
Matter is defined as anything that occupies space and has mass. It is the substance that constitutes the entire universe, from the smallest grain of sand to the largest star in the sky.
Everything around us, including the air we breathe, the food we eat, stones, clouds, stars, plants, animals, and even a tiny drop of water or a grain of sand—everything is matter.
Universal Presence: Everything, from solids to gases, is made of matter.
Historical Context: Ancient Indian philosophers identified matter as five basic elements: air, earth, fire, sky, and water, known as the ‘Panch Tatva’.
Focus of the Chapter: This chapter explores the physical properties of matter and its various states—solid, liquid, and gas.
By understanding these concepts, you’ll gain insight into the material world that surrounds us.
Physical Nature of Matter
The physical nature of matter refers to its fundamental properties and behaviour, as observed and studied through scientific inquiry. The main properties of matter are:
1. Matter is made up of Particles
Matter is made up of particles. These particles can be atoms, molecules, or ions, depending on the specific substance.
The particle nature of matter can be demonstrated by a simple activity.
Experiment: (i) Take about 50 ml of water in a 100 ml beaker. (ii) Mark the level of water. (iii) Add some salt to the beaker and stir with the help of a glass rod. (iv) Observe the change in water level.
Observation: (i) It is observed that the crystals of salt disappear. (ii) The level of water remains unchanged.
Explanation: A water molecule consists of hydrogen and oxygen atoms; between hydrogen and oxygen, there are large empty spaces. These empty spaces are known as voids. (When we add salt to the water, it goes into that void. As a result, we do not see any change in volume.)
Conclusion:This activity shows that matter is made of small particles. And there is space between these particles.
2. How Small are these Particles of Matter?
The size of particles of matter can vary widely depending on what type of particle you’re considering and the scale at which you’re measuring.
Let’s perform an experiment.
Procedure
(i) Take a 250 ml beaker and add 100 ml of water to it.
(ii) Now add 2-3 crystals of potassium permanganate (KMnO4) and stir with a glass rod to dissolve the crystals.
(iii) Take 10 ml of this solution and add it to 100 ml of water taken in another beaker.
(iv) Take 10 ml of this diluted solution and put it into 100 ml of water taken in a still another beaker.
(v) Repeat this process 10 times observe the colour of the solution in the last beaker.
Observation: (i) When we add potassium permanganate to water, the colour of the water changes to pink. (ii) Dilution decreases the colour intensity of the solution.
Explanation: (i) A small amount of Potassium permanganate contains millions of its molecules. When we dissolve potassium permanganate in water, its molecules spread uniformly in the solution and give a pink appearance. (ii) Dilution lowers the amount of the particles in a subsequent solution. As a result, we see a lower colour intensity.
Conclusion: This activity proves that matter is made up of tiny particles.
Try yourself:
What happens to the color of water when potassium permanganate is added?
A.It turns green
B.It turns pink
C.It turns blue
D.It stays clear
Characteristics of Particles of Matter
The characteristics of particles of matter encompass a range of properties that describe their behaviour, structure, and interactions. Let’s see those characteristics.
1. Particles of Matter have Space between Them
There are small voids between every particle in matter.
This characteristic is the concept behind the solubility of a substance in other substances.
Activity Aim: To demonstrate the space between particles of matter.
Experiment: (i) Take a glass of water. (ii) Put a teaspoon of salt/sugar and mix them properly.
Observation: The water is still clear.
Explanation: This is because the particles of salt/sugar get into the interparticle spaces between the water particles.
Conclusion: (i) This proves that there are voids between particles of a substance. (ii) If you add more salt/sugar, it will dissolve until all the space between water particles is filled.
2. Particles of Matter are Continuously Moving
If an incense stick (Agarbatti) is lit and placed in one corner of a room, its pleasant smell spreads throughout the whole room quickly.Agarbatti
It demonstrates that the particles of matter possess motion. When we light an incense stick, it produces some gases (vapour) having a pleasant smell.
The particles of these gases, due to motion, spread throughout the entire room. As a result, we can observe the smell of the lit incense stick from a long distance.
This shows that Matters consist of small particles which are moving continuously. This means that particles of matter possess kinetic energy.
Activity Aim: To demonstrate that the Kinetic Energy of particles increases with an increase in temperature.
Experiment: (i) Take two beakers. To one beaker, add 100 mL of cold water, and to the other beaker, add 100 mL of hot water. (ii) Now add some crystals of potassium permanganate or copper sulphate to both the beakers.
Kinetic energy: Kinetic energy of an object is the measure of the work an object can do by virtue of its motion. The kinetic energy is 1/2 mv2. To accelerate an object, we have to apply force. To apply force, we need to do work. When work is done on an object, energy is transferred, and the object moves with a new constant speed. We call the energy that is transferred kinetic energy, and it depends on the mass and speed achieved.
Observation: It is observed that crystals in hot water diffuse and dissolve faster than in a beaker containing cold water.
Conclusion: (i) All substances have some kinetic energy. When we heat a substance, its kinetic energy increases. (ii) Heating water results in an increase in its kinetic energy; as a result, we see that crystals dissolve in a much shorter time. (iii) From these activities, it is observed that when two different forms of matter are brought into contact, they intermix spontaneously. (iv) This intermixing is possible due to the motion of the particles of matter and also due to the spaces between them.
3. Particles of Matter Attract Each Other
There are some forces of attraction between the particles of matter which bind them together. The force of attraction between the particles of the same substance is known as cohesion.
The force of attraction (or cohesion) is different in the particles of different kinds of matter. In general, the force of attraction is maximum in the particles of solid matter and minimum in the particles of gaseous matter.
Activity Aim: To demonstrate the attractive forces between particles of matter.
Experiment: (i) Take a piece of iron wire, a piece of chalk and a rubber band. (ii) Try to break them by hammering, cutting or stretching.
Observation: (i) Hammering a piece of the iron nail does not break the nail but flattens its surface. (ii) Hammering chalk breaks the chalk and gives us powdered chalk. (iii) We can stretch the rubber band to a large length without any break.
Conclusion: (i) Since energy is required to break crystals of matter into particles. (ii) It indicates that particles in the matter are held by some attractive forces; the strength of these attractive forces varies from one matter to another.
Try yourself:
What are particles of matter known to have?
A.Color
B.Light
C.Mass
D.Sound
States of Matter
The three states of matter are the distinct physical forms that matter can take: solid, liquid, and gas.
Three States of Matter
Matter can exist in one of three main states: solid, liquid, or gas.
Solid matter is composed of tightly packed particles. A solid will retain its shape; the particles are not free to move around.
Liquid matter is made of more loosely packed particles. It will take the shape of its container. Particles can move about within a liquid, but they are packed densely enough that volume is maintained.
Gaseous matter is composed of particles packed so loosely that it has neither a defined shape nor a defined volume. A gas can be compressed.
The Solid State
Solid particles are packed closely together.
The forces between the particles are strong enough that the particles cannot move freely; they can only vibrate.
As a result, a solid has a stable, definite shape and a definite volume. Solids can only change shape under force, as when broken or cut.
Fig: Structure of Solids
In crystalline solids, particles are packed in a regularly ordered, repeating pattern.
There are many different crystal structures, and the same substance can have more than one structure.
Example: Iron has a body-centred cubic structure at temperatures below 912°C and a face-centred cubic structure between 912 and 1394°C. Ice has fifteen known crystal structures, each of which exists at a different temperature and pressure.
The Liquid State
A liquid is a fluid that conforms to the shape of its container but that retains a nearly constant volume independent of pressure.
The volume is definite (does not change) if the temperature and pressure are constant.
When a solid is heated above its melting point, it becomes liquid because the pressure is higher than the triple point of the substance.
Intermolecular (or interatomic or interionic) forces are still important, but the molecules have enough energy to move around, which makes the structure mobile.
This means that a liquid is not definite in shape but rather conforms to the shape of its container.
Its volume is usually greater than that of its corresponding solid (water is a well-known exception to this rule).
The highest temperature at which a particular liquid can exist is called its critical temperature.
Fig: Structure of Liquid
The Gaseous State
Gas molecules have either very weak bonds or no bonds at all, so they can move freely and quickly.
Because of this, not only will a gas conform to the shape of its container, it will also expand to completely fill the container.
Gas molecules have enough kinetic energy that the effect of intermolecular forces is small (or zero, for an ideal gas), and they are spaced very far apart from each other; the typical distance between neighbouring molecules is much greater than the size of the molecules themselves.
A gas at a temperature below its critical temperature can also be called a vapor.
A vapour can be liquefied through compression without cooling. It can also exist in equilibrium with a liquid (or solid), in which case the gas pressure equals the vapour pressure of the liquid (or solid).Fig: Structure of Gas
Asupercritical fluid (SCF) is a gas whose temperature and pressure are greater than the critical temperature and critical pressure. In this state, the distinction between liquid and gas disappears. A supercritical fluid has the physical properties of a gas, but its high density lends it the properties of a solvent in some cases. This can be useful in several applications. Example: Supercritical carbon dioxide is used to extract caffeine in the manufacturing of decaffeinated coffee.
Try yourself:
What shape does a solid retain?
A.Liquid shape
B.Variable shape
C.Defined shape
D.No shape
Also read: Case Based Question Answer: Matter in Our Surroundings
Can Matter Change Its State?
A substance may exist in three states of matter i.e., solid, liquid or gas, depending upon the conditions of temperature and pressure.
By changing the conditions of temperature and pressure, all three states could be obtained (solid, liquid, gas). On heating, solid changes into a liquid, which on further heating changes into a gas. Example: Water exists in all three states. Solid: Ice, Liquid: Water, Gas: Water Vapour.
Ice is a solid state and may be melted to form water (liquid) which on further heating changes into steam (gas). These changes can also be reversed on cooling.
Note:
– Changing a solid to a liquid is called melting.
– Changing a liquid to solid is called solidification.
– Changing a liquid to gas is called vaporization.
– Changing a gas to liquid is called condensation.
– Changing a solid to gas directly is called sublimation. – Changing a gas to solid directly is called deposition.
Temperature and pressure are the two factors which decide whether a given substance would be in a solid, liquid or gaseous state.
1. Effect of Change of Temperature
Let’s Start with an activity
The effect of temperature on three states of matter could be seen by performing the following activity.
Procedure (i) Take a piece of about 100 – 150 g of ice in a beaker. (ii) Hang a thermometer in it so that its bulb is in contact with ice. (iii) Start heating the beaker slowly on a low flame. (iv) Note down the temperature when ice starts changing to water & ice has been converted to water. (v) Record all observations for the conversion of solid ice into liquid water. (vi) Now, place a glass rod in the beaker and slowly heat the beaker with constant stirring with help of a glass rod. (vii) Note the temperature when water starts changing into water vapour. (viii) Record all observations for the conversion of water in the liquid state to the vapour state.
Observation: It is observed that as the temperature increases, the ice starts changing into water. This change is called “Melting“. The temperature remains the same till all the ice changes into water. The thermometer shows 0°C until all the ice has melted. On further heating, the temperature starts rising. At 373 K (or 100°C), water starts boiling. As the water continues to boil, the temperature remains almost constant.
Conclusion of the above activity: This experiment demonstrates that we can change the physical state of matter by heating (Solid → Liquid → Gas).
(a) Melting of Ice
When we increase the temperature of a solid, the kinetic energy of its particles also increases. This is because the particles start to vibrate more quickly. As the kinetic energy increases, it becomes strong enough to overcome the forces of attraction holding the particles together in fixed positions.
Eventually, the particles are able to break free from their fixed positions and start moving more freely, leading to the melting of the solid into a liquid. The melting point is the minimum temperature at which this happens, and it varies depending on the strength of the forces of attraction between the particles.
For example, the melting point of ice is 273.15 K (or 0°C ). The process of melting, also known as fusion, occurs when a solid is heated to its melting point.
During the melting process, the temperature of the substance remains constant, even though heat is still being supplied. This is because the heat energy is being used to overcome the forces of attraction between the particles, rather than increasing the temperature.
The heat energy required to change 1 kg of a solid into a liquid at its melting point is called the latent heat of fusion. This energy is absorbed by the particles without causing a rise in temperature, which is why it is called latent, meaning hidden.
(b) Boiling of Water
When we heat water at 0°C (273 K), the particles have more energy compared to those in ice at the same temperature. As we continue to supply heat to the water, the particles move even faster. Eventually, they reach a point where they have enough energy to overcome the forces of attraction between them, and the liquid starts to change into a gas.
The temperature at which a liquid begins to boil at atmospheric pressure is called its boiling point. Boiling is a process that occurs throughout the bulk of the liquid, where particles gain enough energy to change into the vapour state. For water, this temperature is 373 K (100°C). To convert temperatures between the Kelvin and Celsius scales, we subtract 273 from the Kelvin temperature to get the Celsius temperature, and vice versa. For example, 0°C = 273 K.
The latent heat of vaporisation is the amount of heat energy required to change 1 kg of a liquid into gas at its boiling point and atmospheric pressure. This energy is absorbed by the particles in the form of latent heat, which is why particles in steam at 373 K (100°C) have more energy than those in water at the same temperature.
(c) Sublimation This shows that we can change the state of matter by altering the temperature. While most substances change from solid to liquid and then to gas when heated, some can change directly from solid to gas and vice versa without passing through the liquid state. This process is called sublimation when going from solid to gas, and deposition when going from gas to solid.
Lets understand Sublimation and Deposition of Camphor with an Activity
Take some camphor and crush it into small pieces. Place the crushed camphor in a china dish. Cover the dish with an inverted funnel.
To the stem of the funnel, place a cotton plug. This setup will help in observing the process of sublimation and deposition.
Sublimation of camphor
Observe the camphor over time. You will notice that the camphor starts to sublimate, which means it changes from solid to gas without passing through the liquid state. The gas will then deposit on the cooler parts of the funnel, changing back into solid. This process demonstrates sublimation and deposition.
2. Effect of Change of Pressure
By applying pressure, particles of matter can be brought close together
Solid Carbon Dioxide (Dry Ice): Solid carbon dioxide, commonly known as dry ice, is stored under high pressure. When the pressure is reduced to 1 atmosphere, dry ice sublimates directly into gas without passing through the liquid state. This phenomenon occurs because of the specific conditions of pressure and temperature.
Influence of Pressure and Temperature: The state of a substance—whether it is a solid, liquid, or gas—is determined by the combination of pressure and temperature. By applying pressure and reducing temperature, gases can be liquefied. Conversely, changing the pressure and temperature can also lead to different states of matter.
Gaseous State under Pressure: When pressure is applied to a gas, the particles are forced closer together. This can lead to a change in the state of matter. For example, increasing pressure on a gas while reducing temperature can cause it to liquefy.
Try yourself:
What can happen to matter?
A.It can become invisible.
B.It can disappear.
C.It can grow.
D.It can change its state.
Evaporation
The process of a liquid changing into vapour (or gas) even below its boiling point is called evaporation
Evaporation of a liquid can take place even at room temperature, though it is faster at higher temperatures. It is a surface phenomenon because it occurs at the surface of a liquid only. Whatever the temperature at which evaporation takes place, the latent heat of vaporisation must be supplied whenever a liquid changes into a vapour (or gas).Evaporation
Explanation about Evaporation
Some particles in a liquid always have more kinetic energy than others. So, even when a liquid is well below its boiling point, some of its particles have enough energy to break the forces of attraction between the particles and escape from the surface of the liquid in the form of vapour (or gas).
Thus, the fast-moving particles (or molecules) of a liquid are constantly escaping from the liquid to form vapour (or gas).
Examples: (i) Water in ponds changes from liquid to vapour without reaching the boiling point. (ii) Water, when left uncovered, slowly changes into vapours. (iii) When we put wet clothes out to dry, the water from the clothes goes to the atmosphere.
Differences between Evaporation and Boiling
Also read: Case Based Question Answer: Matter in Our Surroundings
Factors Affecting Evaporation
There are five factors which affect the rate of evaporation:
1. Nature of liquid: Different liquids have different rates of evaporation. A liquid having weaker interparticle attractive forces evaporates at a faster rate because less energy is required to overcome the attractive forces. Example: Acetone evaporates faster than water.
2. The surface area of the liquid: The evaporation depends upon the surface area. If the surface area is increased, the rate of evaporation increases because the high-energy particles from the liquid can go into the gas phase only through the surface. Example: (i) The rate of evaporation increases when we put kerosene or petrol in an open china dish than in a test tube. (ii) Clothes dry faster when they are well spread because the surface area for evaporation increases.
3. Temperature: The Rate of evaporation increases with an increase in temperature. This is because with the increase in temperature number of particles gets enough kinetic energy to go into the vapour state (or gaseous state). Example: Clothes dry faster in summer than in winter.
4. Humidity in the air: The air around us contains water vapour or moisture. The amount of water present in the air is referred to as humidity. The air cannot hold more than a definite amount of water vapour at a given temperature. If the humidity is higher, the rate of vaporisation decreases. The rate of evaporation is higher if the air is dry. Example: Clothes do not dry easily during the rainy season because the rate of evaporation is less due to high moisture content (humidity) in the air.
5. Wind speed: The rate of evaporation also increases with an increase in the speed of the wind. This is because with an increase in the speed of wind, the particles of water vapour move away with the wind, resulting in a decrease in the amount of vapour in the atmosphere. Example: (i) Clothes dry faster on a windy day. (ii) In a desert cooler, an exhaust fan sucks the moist air from the cooler chamber, which results in a greater rate of evaporation of water and hence greater cooling.
How does Evaporation cause Cooling?
During evaporation, cooling is always caused. This is because evaporation is a phenomenon in which only the high-energy particles leave the liquid surface. As a result, the particles having low energy are left behind. Therefore, the average molecular energy of the remaining particles left in the liquid state is lowered. As a result, there is a decrease in temperature on the part of the liquid that is left. Thus, evaporation causes cooling.
Examples: (i) When we pour some acetone on our palm, we feel cold. This is because the particles gain energy from our palms or surroundings and leave the palm feeling cool. (ii) We sprinkle water on the root or the open ground after a sunny, hot day. This cools the roof or open ground. This is because the large latent heat of vaporisation of water helps to cool the hot surface.
Some other examples of Evaporation
We should wear cotton clothes in hot summer days to stay cool and comfortable: This can be explained as follows. We get a lot of sweat on our bodies on hot summer days. Cotton is a good absorber of water, so it absorbs the sweat from our body and exposes it to the air for evaporation. The evaporation of this sweat cools our body. Synthetic clothes (made of polyester, etc.) do not absorb a lot of sweat, so they fail to keep our bodies cool in summer.
We see water droplets on the outer surface of a glass containing ice-cold water: Take some ice-cold water in a glass. Soon we will see water droplets on the outer surface of the glass.
The water vapour present in the air, on coming in contact with the cold glass of water, loses energy and gets converted to the liquid state, which we see as water droplets.
Water keeps cool in the earthen pot (matki) during summer: When the water oozes out of the pores of an earthen pot, during hot summer, it evaporates rapidly. As the cooling is caused by evaporation, therefore, the temperature of the water within the pot falls, and hence it becomes cool.
Earthen Pot
Rapid cooling of hot tea: If the tea is too hot to sip, we pour it into the saucer. In doing so, we increase the surface area and the rate of evaporation. This, in turn, causes cooling and the tea attains the desired temperature for sipping.
A wet handkerchief is placed on the forehead of a person suffering from a high fever: The logic behind placing a wet cloth is that as the water from the wet cloth evaporates, it takes heat from the skull and the brain within it. This, in turn, lowers the temperature of the brain and protects it from any damage due to high temperature.
We often sprinkle water on the road in summer: The water evaporates rapidly from the hot surface of the road, thereby taking heat away from it. Thus, the road becomes cool.
Try yourself:
What process involves a liquid turning into a gas?
Q: Can you name the things that Khushi has drawn ? Write in the boxes given.
Ans:
Activity 1 (Page 124)
Understand your Classroom
Draw a picture of your classroom in your notebook. Label the things that you have drawn.
Khushi is curious, “Where have all these things come from? Who has made them? What are they all made of?” she thought.
Let us help Khushi find out.
The table and chair are made of wood. Where do we get wood from?
The hinges, nails and latches of the door are made of some metals.
Ans: Students are encouraged to attempt it on their own.
Activity 2 (Page 125)
Spot the Metals
Find as many things or parts of things, that are made of metals. Which metals do you recognise around you? If you do not know the name of the metal, ask your friends or an elder. Make a list of these metals in your notebook.
Ans: I looked around and found many things made of metals. Some of the items I found include:
Door hinges – made of iron
Spoon – made of stainless steel
Water tap – made of brass
Coins – made of copper or nickel
Scissors – made of steel
Activity 3 (Page 126)
Seeing through things
Collect a few small objects of different materials from your surroundings like bottles, papers, cloth, and utensils, etc. Look at a light bulb or a candle flame through them. You can see through some objects very clearly, you can partially see through some others, while you cannot see through some objects at all. Order these objects from those you can see through very clearly, to those you cannot see through at all.
Ans:
See through clearly : Clear glass bottle , Clear Plastic Bottle , Clean Water
See through Partially : Frosted glass, Butter Paper, Thin Fabric
Cannot see through at all : Wooden door , Book, Metal
Activity 4 (Page 127)
Let us colour the world!
Collect two or three see-through bags, bottles or thin cloth of different colours. Look at a sheet of white paper through them.
Does the colour of the paper appear to change?
Does white paper appear different when you look at it through thin blue plastic or glass? Or, thin yellow plastic or glass?
Do the colours of different objects appear to change? How did a blue object look through thin yellow plastic?
Have you earlier experienced looking through coloured transparent objects? Try to recall such experiences.
Ans: Students are encouraged to attempt it on their own.
Write (Page 128)
Chain Game
In the table below, Khushi has grouped objects according to the materials that they are made of. Her list of objects is in the first column of the table. The names of the materials are in the second column. The third column of the table is for you to complete. Here write the names of some objects you have seen that are made from that material. Some objects around you may be made from materials not in this list, e.g., clay and rubber are missing in Khushi’s list. Use one of these to add an additional row in the table.
Q: Where do all these materials come from ? Can you locate their source ?
For Example, Wood – Tree
Metals – ____________
Cloth – ______________
Ans:
Metals — Metals are extracted from ores, which are found in the Earth.
Cloth — Cloth is made from natural fibers like cotton (from plants) or wool (from animals) or synthetic materials such as polyester.
Find out (Page 129)
Talk to your Grandparents
In their childhood, were these things made of the same materials?
Are there new materials now that they might not have seen before?
Are there any materials that they saw in their childhood that are not in use now? Why?
Ans: Yes, materials can differ in various ways, not just how they look. For example, texture, weight, etc.
Find out
What material is your spoon made of?
Ans: My spoon is made up of Steel.
Is it made of metal, wood or some other material? Can you guess?
Ans: Steel is an Alloy.
Which of these words or phrases describes the spoon?
Ans: The Spoon is Smooth and Shiny.
Activity 5 (Page 130)
Knock on it and it will speak to you! Orchestra
Take a metal spoon and at least five objects made up of different materials-wood, metal, plastic, cloth and glass. Gently tap the spoon on each of them. Listen to the sound that each of them makes. Make your own words to describe all these different sounds.
Ans: Students are encouraged to attempt it on their own.
Write (Page 130)
Odd Pairs
Q: List five objects and pair them with a material that is not suitable for it! Explain why these materials will not work to make these objects. One example is done for you.
Ans:
Activity 6 (Page 132)
Let’s group them another way!
Here are the names of some objects: ink, a stone, smoke, ice, steam, a spoon, honey, a bottle, a bag, and water.
If it is a solid, write its name on the tray; if it is a liquid, write it in the bottle; if it is a gas, write it in the balloon.
Add some of your objects in the tray, bottle, and balloon.
Ans:
Q: Some objects could be confusing, such as sand sponge, or clay. Identify more such objects and write the names of at least three of them.
Ans: Cotton Candy , Silica Gel and Pumice Stone
Natural — Artificial (Page 133)
Q: List out five things in each group.
Ans:
Natural: Tree, Mango, Bird, Rock, Water
Artificial: Clothes, Shoes, Table, Car, Book
Find Out
Have you seen trees around you that bear flowers and fruits at special times of the year?
Ans: Yes, I have seen trees that bear flowers and fruits at special times of the year. For example:
(i) Mango trees have flowers in February-March and fruits in June-July.
(ii) Guava trees give fruits in winter (November-December).
(iii) Apple trees grow fruits in summer (July-August).
Different trees have different seasons for flowers and fruits!
If you have ever eaten a ripe mango or seen mangoes in the market or watched a mango tree through the year, try to guess— at what time of the year did Khushi draw her picture?
Ans: Khushi most likely drew her picture in June, because mangoes ripen during the summer season. During this time, mango trees are full of ripe mangoes, and we can see them in the markets.
Could it be around January or around June?
Ans: It could be around June because mangoes ripen in the summer season. During this time, mango trees are full of ripe mangoes, and we can see them in the market. In January, mango trees usually have flowers but not ripe fruits.
Let us Reflect (Page 134)
A. Write
Q: Things around us are made of different types of materials. Write down the names of three materials we commonly see around us.
Ans:
Wood
Metal
Plastic
B. Discuss
Q: Suppose you find a shining spoon. You don’t know if it is made of metal or whether it is made of some other material and then painted with shiny paint. How would you find out?
Ans: I would tap the spoon on a hard surface and listen to the sound it makes. A metal spoon would make a distinct ringing sound. I could also check the weight and feel of the spoon, as metal spoons are generally heavier and feel cooler to the touch than painted plastic spoons.
C. Draw
Q: Draw three natural and three artificial things.
Q1: Write numbers 1, 2, 3 for lightest to heaviest for the following: a toffee, an ice-cream, a lollipop Ans: 1,3,2
Q2: Arrange the containers according to their capacity in ascending order: Spoon, Mug, Bucket, Glass Ans: Spoon, Glass, Mug, Bucket
Q3: Which is heavier in weight? (a) Almirah (b) Book Ans: (a) Almirah Q4: Which is heavier in weight? (a) Weight of your mother (b) Your weight Ans: (a) Weight of your mother
Q5: Which is heavier in weight? (a) Scissors (b) Nail Ans: (a) Scissors Q6: Choose the correct measuring unit: Capacity of a glue bottle is measured in _________. (a) cm (b) g (c) ml Ans: (c) ml
Q7: Which is heavier in weight? (a) Tennis Ball (b) Football Ans: (b) Football Q8: Which is heavier in weight? (a) 2 Books (b) Your school bag Ans: (b) Your school bag Q9: Which is heavier in weight? (a) Water Bottle (b) Glass of Water Ans: (a) Water Bottle Q10: Write H for heavy and L for light for the following: a leaf Ans: L
A number is a value we use for counting and calculating. Numbers can be shown in different ways: as words (one, two, three) or as figures (1, 2, 3). We can also group numbers by how many digits they have.
Single-digit numbers have only one digit, for example 1, 2, 3, 4.
Two-digit numbers have two digits, for example 10, 25, 99.
Three-digit numbers have three digits, for example 100, 345, 897.
Now, students, can you count how many flowers there are?
By counting these, we can see that there are a total 36flowers.
Step Counting
Let us now read an interesting story!.
Once upon a time, there was a little kangaroo named Skip who loved counting. Regular counting was slow for Skip, so he invented step counting.
Instead of going one by one, he jumped ahead or backwards by a fixed number each time. His friends liked it and soon everyone in the jungle was step counting, making counting fun and fast!
What is Step Counting?
Step counting means counting numbers by adding the same amount each time. For example, if you add 2 each time, you count 0, 2, 4, 6, 8, …
Backward skip counting is counting in reverse. Instead of going forward, you start from a larger number and subtract a certain amount each time to reach the next number. It’s just like walking backwards but with numbers. For example, counting backwards by 3 from 10 gives 10, 7, 4, 1.
Step counting helps you see number patterns and makes counting faster and more fun.
Forward Step Counting
In forward step counting we start at a number and keep adding the same amount to get the next number.
Skip count by 2
Start at 0 and add 2 each time.
0 + 2 = 2
2 + 2 = 4
4 + 2 = 6
6 + 2 = 8
Continue this process: 10, 12 and so on until 12 or further.
You can skip count starting at any number. For example, skip count by 2 starting at 5 gives:
5, 7, 9, 11, 13 …
Skip count by 5
In skip counting by 5, we add 5 each time and move forward.
If Skip the kangaroo starts from 5 and skips by 5, the numbers he reaches are:
5 + 5 = 10
10 + 5 = 15
15 + 5 = 20
So the series is 5, 10, 15, 20, …
Skip count by 10
Look at the picture of the kangaroo jumping. Complete the pattern by finding how much it jumps each time.
We can see that the kangaroo first jumps from 0 to 10, then from 10 to 20.
We can use subtraction to find the jump size: 20 – 10 = 10.
Also 10 – 0 = 10, so the difference is 10.
Thus, to continue the series we add 10 each time.
The complete series is: 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100.
Backward Skip Counting
What we have learned so far is called forward skip counting, which implies we are counting in the forward direction and adding a certain number to each previous number to obtain the next number in the series.
Now, we will discuss backward skip counting.
Backwards skip counting is a way of counting numbers in reverse order by skipping a certain amount each time. Instead of starting from a lower number and counting up, you start from a higher number and count down. For example, if you’re skip counting backward by 3s from 10, it would go like this: 10, 7, 4, 1.
Backwards skip count by 3
Start with a number and subtract 3 each time.
Starting from 100:
100 – 3 = 97
97 – 3 = 94
94 – 3 = 91
91 – 3 = 88
The series is: 100, 97, 94, 91, 88, … These numbers are in descending order.
Backwards skip count by 20
Let’s imagine we’re on a backwards adventure, counting by 20s. Instead of walking forward, we’re taking big jumps backwards.
Start at 100 and subtract 20 each time:
100 (start)
80 (100 – 20) – we took one step back, like a giant leap!
60 (80 – 20) – another big step backward
40 (60 – 20) – we’re really moving now!
20 (40 – 20) – almost there!
0 (20 – 20) – and we’ve reached the end of our backward journey!
Guess My Place
Now, let us play a game in which we guess where the ants are sitting on a number line.
Look at the number line, and answer the following questions:
(a) Which number is the red ant sitting on? (b) Which number is the blue ant sitting on? (c) Which number is Brown Ant sitting on?
First fill the number line from 10 to 110 with equal gaps of 10: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110.
Answers: (a) Red ant is sitting at number 20. (b) Blue ant is sitting at 50. (c) Brown ant is sitting on number 90.
Exploring Patterns
Q: Look at the number chart and write down the answers.
__9___ comes just before 10 __19___ comes just before 20 __29___ comes just before 30 __39___ comes just before 40
Q: What is the pattern here?
Ans: Let us subtract to see the difference. 19 – 9 = 10 29 – 19 = 10 39 – 29 = 10 We can clearly see that the difference is 10. The pattern continues: 9, 19, 29, 39, 49, 59, …
Q: Now, look at the numbers coloured purple in the number chart. Write them.
Ans: The difference is 9. Nine has been added to each number.
Look at this fun number window
Using the number window, we can find numbers above, below, left and right of a given number by adding or subtracting 1 or 10.
Fill in the blocks given below:
Observe how blocks are placed and extend the pattern further.
To find the block above 55, subtract 10: 55 – 10 = 45.
To find the block below 55, add 10: 55 + 10 = 65.
Now, moving on to the above row, we have found the middle block, which is 45. To find out the block on its left, we need to subtract 1 from it. 45-1 = 44 To find out the number on its right, we need to add 1 to 45 which gives us 46. Similarly, we find out the numbers in the last row.
Let’s look at some more examples of number grids:
1.
Using the same logic, add numbers to this grid:
2.
Let’s fill up this magic grid:
Hope you enjoyed playing with numbers and exploring different games. Keep practising and having fun!
Motion
Types of Motion
Motion along a straight line
Example of Zero Displacement
Given:
(ii) s/t graph for non-uniform motion:
v = (s2 – s1)/(t2 – t1)
a = (v2 – v1)/(t2 – t1)
a2 ≠ a1
a1‘ = a2‘
Tissue
Intercalary meristem section 
Parenchyma Tissue in Transverse and Longitudinal section
Sclerenchyma Tissue
Epidermis
Xylem Elements
Working of Xylem and Phloem in plant
Section of phloem
Various cells from the human body
Golgi Apparatus
Lysosome
Mitochondria
Plastid
MITOSIS
MEIOSIS
Structure of Atom
Plum Pudding Model
Rutherford’s Experiment
Bohr’s Model
Atomic structure of the first eighteen elements
Examples of Isobars
Example of Law of conservation of Mass
Example of Law of Constant Proportion
John Dalton
Atomic mass of some elements
Atomicity of some non-metals
Examples of Mixtures
Solution, Suspension and Colloidal Solution
Solution of Copper Sulphate does not show Tyndall Effect, Mixture of Water and Milk shows Tyndall Effect
Everything around us, including the air we breathe, the food we eat, stones, clouds, stars, plants, animals, and even a tiny drop of water or a grain of sand—everything is matter.
Agarbatti
Three States of Matter
Fig: Structure of Solids
Fig: Structure of Liquid
Fig: Structure of Gas
Sublimation of camphor
By applying pressure, particles of matter can be brought close together
Evaporation
Earthen Pot
