Easy Chapter Introduction
Everything around us is made of matter.
Matter is made up of extremely small particles called
constituent particles.
These particles are always present, have spaces between them,
attract one another and can move differently in solids, liquids
and gases.
Probe and Ponder
Why is it possible to pile up stones or sand, but not a liquid like water?
Answer: Stones and sand can form a pile because their particles remain together. Water particles can move freely, so water flows instead of forming a pile.
Why does water take the shape of folded hands but lose that shape when released?
Answer: Water is a liquid. Its particles can move, so it takes the shape of the container or folded hands and flows away when released.
We cannot see air, so how does it add weight to an inflated balloon?
Answer: Air is matter and has mass. Therefore, adding air to a balloon increases its weight.
Is the air we breathe today the same that existed thousands of years ago?
Answer: Air is continuously moving and mixing. Some of its particles may have existed thousands of years ago, while others have changed places and mixed with the atmosphere.
Share your questions
Think and write: Write any question you have about matter and its particles.
7.1 What Is Matter Composed of?
Easy Concept
Matter is made up of a very large number of extremely small particles.
These are called constituent particles.
A large piece of chalk can be broken into smaller and smaller pieces.
Even after grinding, the chalk remains chalk. This is a
physical change.
Activity 7.1: Let us explore
Chalk is broken, ground into powder and observed with a magnifying glass.
The tiny grains are still chalk. This shows that a substance is made of
very small particles.
What do you observe?
Answer: We observe very tiny grains of chalk powder. Each grain is still chalk.
Each tiny grain you observe is still a speck of chalk.
Is every speck of this fine chalk powder still composed
of the same substance, or has it changed into
something else on breaking or grinding?
Answer: Every speck is still made of chalk. Grinding only reduces its size; it does not make a new substance.
Remember: Grinding chalk is a physical change because no new substance is formed.
Constituent Particles
The basic tiny units that make up a substance are called
constituent particles.
Chalk, sand and clay are all made up of very large numbers of
constituent particles.
Activity 7.2: Let us perform
Sugar is added to water and allowed to dissolve. After dissolving,
sugar cannot be seen, but the water tastes sweet.
Does the water taste sweet?
Answer: Before complete dissolving, the top layer may not taste sweet. After stirring and complete dissolving, it tastes sweet.
What difference in taste do you notice? Does it taste sweet?
Answer: After the sugar dissolves completely, the water tastes sweet throughout.
Do you observe any sugar particles in the solution?
Answer: No. The sugar particles are too small to be seen, but they are present in the solution.
But where did the sugar go?
Answer: Sugar breaks into tiny constituent particles. These particles spread into the spaces between water particles.
Interparticle spaces: The spaces between the particles of matter are called interparticle spaces.
7.2 What Decides Different States of Matter?
Particles of matter attract one another. These attractive forces are called
interparticle attractions.
The strength of attraction depends on the substance and the distance between its particles.
Important: Strong attraction keeps particles close together. Weaker attraction allows particles to move more freely.
Our Scientific Heritage
Acharya Kanad, an ancient Indian philosopher, spoke about the idea of
Parmanu, meaning a tiny indivisible particle. His ideas
were written in the Vaisheshika Sutras.
7.2.1 Solid State
Solids have a fixed shape and a fixed volume.
Their particles are tightly packed and have strong interparticle attraction.
In which of the above six objects do you think particles are strongly held together?
Answer: In all the solid objects, the particles are held together. Hard objects such as iron, rock salt, stone and aluminium have strong attractions.
In the solid state, is there any way to move these particles apart?
Answer: Heating a solid gives its particles more energy. At sufficiently high temperature, particles move farther apart and the solid melts.
Particle Arrangement in a Solid
Solid
Closely packed particles
Melting
When a solid is heated, its particles vibrate more strongly.
At the melting point, particles begin leaving their fixed positions
and the solid changes into a liquid.
Melting point: The minimum temperature at which a solid melts into a liquid at atmospheric pressure.
| S.No. | Material | Melting point |
|---|
| 1 | Ice | 0 °C |
| 2 | Urea | 133 °C |
| 3 | Iron | 1538 °C |
Solids have a definite volume; what about liquids and gases?
Answer: Liquids have a definite volume but no fixed shape. Gases have neither a fixed shape nor a fixed volume.
7.2.2 Liquid State
Liquids have a fixed volume but no fixed shape.
They take the shape of the container.
Activity 7.4: Let us try and find out
Are you able to move your finger through the water?
Answer: Yes. Water particles can move aside and then come together again.
In liquids, particles can move freely within a limited space.
Their attraction is weaker than in solids but strong enough to keep the particles close.
Boiling
When a liquid is heated, its particles move faster. At the boiling point,
particles gain enough energy to escape and the liquid changes into vapour.
Boiling point: The temperature at which a liquid boils and changes into vapour at atmospheric pressure.
Evaporation: Slow conversion of a liquid into vapour from its surface. It can occur below the boiling point.
I have seen that spilled water disappears after some time, and it happens at any temperature!
Answer: This happens because of evaporation. Water particles escape slowly from the surface even below the boiling point.
7.2.3 Gaseous State
Gases have no fixed shape and no fixed volume.
Their particles move freely in all directions.
Activity 7.5: Let us investigate
Observe how the smoke spreads inside the Gas Jar B.
Answer: Smoke spreads throughout Gas Jar B and occupies the available space.
Do gases also have a fixed volume?
Answer: No. Gases do not have a fixed volume. They expand to occupy the available space.
Gas
Particles are far apart
Both liquids and gases can flow. Therefore, liquids and gases are called
fluids.
Safety: Incense sticks and iodine should be used carefully and under proper supervision.
7.3 How Does the Interparticle Spacing Differ in the Three States of Matter?
Activity 7.6: Let us experiment
What do you observe?
Answer: The volume of air inside the syringe decreases when the plunger is pushed.
What can we say about the behaviour of gas in the syringe?
Answer: Gas can be compressed because there is a lot of space between its particles.
Gas: Easily compressible because its particles have large interparticle spaces.
Water: Practically incompressible because its particles are already close together.
Activity 7.7: Let us observe
Predict whether the water level will increase or decrease with respect to the mark B.
Answer: After sugar dissolves, the level may decrease somewhat from mark B because sugar particles occupy spaces between water particles.
What difference do you observe in the water levels?
Answer: The level first increases when sugar is added and then may decrease after the sugar dissolves.
Repeat the Activity 7.7 with some other soluble solids, such as common salt or glucose, and insoluble solids, like sand and stone pieces.
What do you observe in each case? Do the sand particles dissolve? Does the volume of water in the vessel change, and why?
Answer: Salt and glucose dissolve in water. Sand and stone pieces do not dissolve. Insoluble particles settle and occupy space, so the volume increases.
Sugar and sand are both solids. Why does sugar dissolve in water but sand does not?
Answer: Sugar particles can separate and mix with water particles. Sand particles do not separate in the same way, so sand remains undissolved.
What do you think about the interparticle spacing in solids?
Answer: Solids have very small spaces between their closely packed particles, although the particles are not completely without space.
A Step Further
The word particle can have different meanings. Suspended Particulate Matter (SPM) refers to tiny dust particles suspended in air. These dust particles are themselves made up of extremely small constituent particles such as atoms and molecules.
7.4 How Particles Move in Different States of Matter?
Particles in matter are always moving. Their movement depends on the state of matter and the amount of thermal energy.
Activity 7.8: Let us experiment
What do you observe?
Answer: Pink colour from potassium permanganate gradually spreads through the water until the water becomes uniformly pink.
Do you know why this happens?
Answer: Water particles are continuously moving and spread the potassium permanganate particles throughout the water.
Think like a scientist — Try it yourself!
What do you observe?
Answer: Potassium permanganate spreads fastest in hot water, slower in room-temperature water and slowest in ice-cold water.
Key idea: When heat is supplied, particles move faster.
Try to depict it by drawing a diagram.
Answer: Draw three glasses. Show the particles spreading slowly in cold water, faster in room-temperature water and fastest in hot water.
Activity 7.9: Let us find out
Do you notice the fragrance from a distance?
Answer: Yes. The fragrance spreads through the air because gas particles are constantly moving.
Can you share a few other real-life situations where you have experienced the movement of gas particles?
Answer: The smell of perfume spreading through a room, the smell of food reaching another room and the smell of flowers spreading through air are examples.
Easy Notes — Three States of Matter
| Property | Solid | Liquid | Gas |
|---|
| Particle spacing | Minimum | More than solids | Maximum |
| Particle arrangement | Closely packed | Loosely packed | Far apart |
| Attraction | Strongest | Weaker than solids | Very weak/negligible |
| Shape | Fixed | No fixed shape | No fixed shape |
| Volume | Fixed | Fixed | No fixed volume |
| Particle movement | Small vibrations | Move within limited space | Move freely in all directions |
Let Us Wrap Up!
1. Matter is made up of extremely small particles.
2. Particles have spaces between them.
3. Particles attract one another.
4. Solids have the strongest attraction.
5. Liquids have weaker attraction than solids.
6. Gases have very weak or negligible attraction.
7. Heating gives particles more thermal energy.
8. More thermal energy makes particles move faster.
9. Solids have fixed shape and volume.
10. Liquids have fixed volume but no fixed shape.
11. Gases have neither fixed shape nor fixed volume.
Keep the Curiosity Alive
1. Choose the correct option.The primary difference between solids and liquids is that the
constituent particles are:
(i) closely packed in solids, while they are stationary in
liquids.
(ii) far apart in solids and have fixed position in liquids.
(iii) always moving in solids and have fixed position in
liquids.
(iv) closely packed in solids and move past each other in
liquids.
Answer: (iv) closely packed in solids and move past each other in liquids.
2. Which of the following statements are true? Correct the false
statements.(i) Melting ice into water is an example of the
transformation of a solid into a liquid.
(ii) Melting process involves a decrease in interparticle
attractions during the transformation.
(iii) Solids have a fixed shape and a fixed volume.
(iv) The interparticle interactions in solids are very strong,
and the interparticle spaces are very small.
Answer:
(i) True.
(ii) True. Heating weakens the effective interparticle attraction as particles move farther apart.
(iii) True.
(iv) True.
(v) When we heat camphor in one corner of a room, the
fragrance reaches all corners of the room.
Answer: True. Camphor particles spread through the air because gas particles are continuously moving.
(vi) On heating, we are adding energy to the camphor, and
the energy is released as a smell.
Answer: False. Heating gives energy to camphor and helps its particles escape and spread through the air. The smell is due to these particles reaching our nose.
3. Choose the correct answer with justification. If we could
remove all the constituent particles from a chair, what would
happen?(i) Nothing will change.
(ii) The chair will weigh less due to lost particles.
(iii) Nothing of the chair will remain.
Answer: (iii) Nothing of the chair will remain. A chair is made of constituent particles. Removing all of them means removing the matter of the chair.
4. Why do gases mix easily, while solids do not?
Answer: Gas particles are far apart and move freely in all directions. Solid particles are closely packed and cannot move freely.
5. When spilled on the table, milk in a glass tumbler, flows and
spreads out, but the glass tumbler stays in the same shape.
Justify this statement.
Answer: Milk is a liquid, so its particles can move and it spreads. Glass is a solid, so its particles are strongly held and its shape remains fixed.
6. Represent diagrammatically the changes in the arrangement of particles as ice melts and transforms into water vapour.
Answer: Draw particles closely packed in ice, slightly farther apart in water and very far apart in water vapour.
7. Draw a picture representing particles present in the
following:(i) Aluminium foil
(ii) Glycerin
(iii) Methane gas
Answer:
(i) Aluminium foil — draw particles very closely packed.
(ii) Glycerin — draw particles somewhat loosely packed.
(iii) Methane gas — draw particles very far apart.
8. Observe Fig. 7.16a which shows
the image of a candle that was just
extinguished after burning for some
time. Identify the different states of
wax in the figure and match them with
Fig. 7.16b showing the arrangement of
particles.
Answer: Solid wax has closely packed particles. Melted wax has particles that can move past each other. Wax vapour has particles much farther apart.
9. Why does the water in the ocean
taste salty, even though the salt is not
visible? Explain.
Answer: Salt dissolves into very tiny particles and spreads throughout the water. The particles are too small to see but can be tasted.
10. Grains of rice and rice flour take the shape of the container when placed in different jars. Are they solids or liquids? Explain.
Answer: They are solids. Each grain or particle remains solid. The collection of many small grains can flow and take the shape of a container, but the individual particles do not lose their solid nature.
Why?
Answer: Use this section to write your own questions beginning with “Why?”
When?
Answer: Use this section to write your own questions beginning with “When?”
How long?
Answer: Use this section to write your own questions beginning with “How long?”
Where? Why not?
Answer: Use these prompts to frame questions based on the chapter.
Prepare some questions based on your learnings so far …………………………………………………………………………….
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Sample questions:
1. Why do gases occupy the whole container?
2. Why do solids have a fixed shape?
3. Why does sugar dissolve in water?
4. Why does heating make particles move faster?
Reflect on the questions framed by your
friends and try to answer …………………………………………………………………………….
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Answer: Discuss your friends’ questions and answer them using the concepts of particles, interparticle spaces, attraction and particle movement.
Discover, Design, and Debate
Fix a balloon over the neck of a bottle and put the bottle in
hot water. Explore what will happen?
Answer: The air inside the bottle gets heated and expands. It pushes into the balloon, so the balloon may inflate.
Design and create simple models to represent particles of
solids, liquids, and gases showing interparticle spacing using
clay balls, beads, etc.
Suggested model: Use tightly packed beads for a solid, loosely arranged beads for a liquid and widely separated beads for a gas.
Pretend to be particles of solids, liquids, and gases, at
different temperatures—create and perform a role-play/
dance showing particles in motion.
Suggested activity: Stand closely and vibrate for a solid. Move around each other within a limited space for a liquid. Move freely in all directions for a gas.
Debate in the class — ‘Gases can spread and fill all the available
space’. Is this property of gases beneficial or harmful?
Answer: It can be both beneficial and harmful. It is useful for breathing and spreading smells, but harmful when poisonous gases spread through the air.
A Step Further
The tiny particles that make up matter are atoms and molecules.
An atom is a very small unit of an element. Some atoms combine to form molecules.
A hydrogen molecule contains two hydrogen atoms. A water molecule contains two hydrogen atoms and one oxygen atom.
Quick Revision Chart
| Concept | Easy Meaning |
|---|
| Matter | Anything made of particles and having mass and occupying space. |
| Constituent particles | Tiny particles that make up matter. |
| Interparticle space | Space between particles. |
| Interparticle attraction | Force of attraction between particles. |
| Solid | Fixed shape and fixed volume. |
| Liquid | Fixed volume but no fixed shape. |
| Gas | No fixed shape and no fixed volume. |
| Melting | Solid changing into liquid. |
| Boiling | Liquid changing rapidly into vapour at its boiling point. |
| Evaporation | Slow surface change of liquid into vapour. |
| Diffusion | Spreading of particles from one place to another. |
One-Minute Revision
Solid → particles close, strong attraction, fixed shape and volume.
Liquid → particles less closely packed, weaker attraction, fixed volume but no fixed shape.
Gas → particles far apart, very weak attraction, no fixed shape or volume.
Heating → particles gain energy and move faster.
Cooling → particles lose energy and move slower.
More interparticle space → particles can move more freely.
More particle movement → greater thermal energy.