Particulate Nature of Matter — Class 8 Science
Curiosity · Chapter 7
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6- Mathematics
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- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
2- Mathematics
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
Chapter summary
Key ideas & terms
- Constituent particle
- The smallest basic unit that makes up a larger piece of a substance, which cannot be broken down further by ordinary means.
- Interparticle force
- The attractive force that holds the constituent particles of a substance together.
- Interparticle space
- The empty space present between the constituent particles of matter.
- Melting point
- The minimum temperature at which a solid changes into a liquid at atmospheric pressure.
- Boiling point
- The temperature at which a liquid boils and changes into vapour at atmospheric pressure.
- Diffusion
- The spreading of particles of one substance through another due to the constant motion of particles.
Extra questions & answers
What does grinding chalk and dissolving sugar tell us about matter?
They show that matter is made of a large number of extremely small constituent particles, and that breaking or dissolving does not change the substance itself.
What holds the constituent particles of a substance together?
Attractive interparticle forces, whose strength depends on the distance between the particles.
Why do solids have a fixed shape and volume?
Their particles are tightly packed with very strong interparticle attraction and can only vibrate about fixed positions.
Why do liquids have a fixed volume but no fixed shape?
Liquid particles have slightly weaker attractions and can move within a limited space, so liquids take the shape of their container but keep a definite volume.
Why do gases have neither fixed shape nor fixed volume?
Interparticle attractions in gases are negligible, so the particles move freely and fill all the available space.
What is the melting point of a solid?
The minimum temperature at which the solid melts to become a liquid at atmospheric pressure.
What does the syringe activity show about gases and liquids?
Gases can be compressed because their particles have large gaps, while water is practically incompressible because its particles are close together.
Why does the volume decrease when sugar dissolves in water?
The dissolved sugar particles occupy the spaces between the water particles, showing that interparticle spaces exist.
What does the spreading of potassium permanganate in water demonstrate?
It demonstrates that water particles are in constant motion and that this motion increases with temperature.
How does thermal energy determine the state of matter?
Low thermal energy keeps particles close in solids, more energy lets them move in liquids, and high energy frees them completely in gases.
Probe and ponder
Why is it possible to pile up stones or sand, but not a liquid like water?
Stones and sand are solids. In solids the constituent particles are closely packed and held by very strong interparticle attractions, so they keep a fixed shape and volume and can be piled. Water is a liquid. Its particles have weaker attractions and a little more space, so they can move past each other and flow. Therefore water has no fixed shape, it takes the shape of its container and cannot be piled.
Why does water take the shape of folded hands but lose that shape when released?
When held in folded hands water takes that shape because liquids have no fixed shape and flow to occupy the shape of the container. The interparticle forces are not strong enough to hold a definite shape. When the hands are opened the support is removed, the water particles are free to flow under gravity, so the water spreads and loses the cupped shape.
We cannot see air, so how does it add weight to an inflated balloon?
Air is matter and is made of extremely small constituent particles. Each particle has mass, even though we cannot see individual particles. An inflated balloon contains a very large number of extra air particles pumped inside it compared to an empty balloon. Their combined mass adds a small but measurable weight to the balloon, which can be shown on a sensitive balance.
Is the air we breathe today the same that existed thousands of years ago?
Yes, in terms of matter. The air is made of particles of gases like nitrogen, oxygen, carbon dioxide and water vapour. These particles are not destroyed easily; they circulate continuously through the atmosphere, are used by plants and animals and released again, and mix globally by wind. So the same kinds of particles have been recycled and spread around the Earth for thousands of years, though their proportions can change slightly.
Share your questions
Example of my own question: If matter is made of tiny particles with empty space between them, why cannot we compress a stone like we can compress air in a syringe?
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.
The correct option is
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.
True. Ice is the solid state of water and on heating to
2. Which of the following statements are true? Correct the false statements. (ii) Melting process involves a decrease in interparticle attractions during the transformation.
True. On heating, the thermal energy makes particles vibrate more vigorously and move slightly apart. Since attraction decreases sharply with distance, the interparticle attractions become weaker, allowing the solid to become a liquid.
2. Which of the following statements are true? Correct the false statements. (iii) Solids have a fixed shape and a fixed volume.
True. Because the interparticle attractions are maximum and the interparticle spaces are minimum, particles in solids cannot move freely and stay in fixed positions, so shape and volume remain fixed.
2. Which of the following statements are true? Correct the false statements. (iv) The interparticle interactions in solids are very strong, and the interparticle spaces are very small.
True. This strong attraction and close packing is the reason solids are rigid, have high density and are almost incompressible.
2. Which of the following statements are true? Correct the false statements. (v) When we heat camphor in one corner of a room, the fragrance reaches all corners of the room.
True. On heating, camphor sublimes into vapour. Its particles separate and move freely in all directions, mixing with air particles by diffusion and filling the available space, so the smell spreads throughout the room.
2. Which of the following statements are true? Correct the false statements. (vi) On heating, we are adding energy to the camphor, and the energy is released as a smell.
False. Heating increases the thermal energy of camphor particles, helping them overcome interparticle forces and escape as vapour. The smell is not energy, it is the actual camphor particles reaching our nose. Corrected statement: On heating we add thermal energy to camphor, which increases particle motion and causes camphor particles to diffuse as vapour; we perceive their presence as fragrance.
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.
Correct answer is
4. Why do gases mix easily, while solids do not?
In gases the interparticle attractions are negligible and the interparticle spaces are maximum. Particles move freely at high speed in all directions and can easily enter the spaces between particles of another gas, so mixing by diffusion is very fast. In solids the attractions are maximum and spaces are minimum, particles are fixed and only vibrate; they cannot leave their positions to intermix without melting or breaking the solid.
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.
Milk is a liquid. Its interparticle attraction is weaker than in a solid and particles can slide past each other, so it has no fixed shape and flows to spread on the table, though its volume stays the same. The glass tumbler is a solid. Its particles are closely packed with very strong attractions and minimum space, so they cannot flow and the tumbler keeps its fixed shape and volume.
6. Represent diagrammatically the changes in the arrangement of particles as ice melts and transforms into water vapour.
Ice
7. Draw a picture representing particles present in the following: (i) Aluminium foil
Aluminium foil is a solid metal. Draw many small circles closely packed in regular rows, touching each other, with almost no gap, representing maximum attraction and minimum space. All particles are held in fixed positions and only vibrate, giving the foil a definite shape and volume.
7. Draw a picture representing particles present in the following: (ii) Glycerin
Glycerin is a viscous liquid. Draw circles that are close but not in a regular order, with small gaps between them, a little more spaced than in a solid. Particles are loosely packed and can move past each other in a limited region, showing definite volume but no fixed shape.
7. Draw a picture representing particles present in the following: (iii) Methane gas
Methane gas
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.
In the candle: the outer hard body of the candle is solid wax, the small pool around the wick is liquid wax formed on heating, and the thin wisp of smoke/wapour rising just after extinguishing is gaseous wax. Matching to particle diagrams: solid wax corresponds to the most closely packed, ordered arrangement with minimum space and maximum attraction; liquid wax corresponds to the slightly looser, disordered arrangement with a little more space; gaseous wax corresponds to the highly spaced, random arrangement where particles are far apart and move freely.
9. Why does the water in the ocean taste salty, even though the salt is not visible? Explain.
Common salt dissolves in water by breaking into its extremely small constituent particles. These particles separate and occupy the interparticle spaces between water particles. They are too small to be seen even with an ordinary microscope, but they are present throughout the solution. When we taste the water, our tongue detects those salt particles, so the sea water tastes salty even though no salt grains are visible.
10. Grains of rice and rice flour take the shape of the container when placed in different jars. Are they solids or liquids? Explain.
They are solids, but in granular form. Each individual grain of rice or each tiny particle of rice flour is a solid with a fixed shape and strong internal interparticle attraction. When many grains are poured together they can pour and appear to take the shape of the jar, like sand, because the grains can slide over each other. A true liquid would have no fixed shape at the particle level and its constituent particles move past each other. Here the flow is of many small solid pieces, not of liquid particles, and each grain retains its own volume and shape.
Discover, design, and debate
Fix a balloon over the neck of a bottle and put the bottle in hot water. Explore what will happen?
The balloon will inflate. The air inside the bottle is a gas with large interparticle spaces. On warming in hot water the thermal energy of the gas particles increases, they move faster and hit the walls more often and push farther apart. The air expands and occupies more volume, flowing into the balloon and stretching it. On cooling the air contracts and the balloon deflates again.
Design and create simple models to represent particles of solids, liquids, and gases showing interparticle spacing using clay balls, beads, etc.
Solid model: press clay balls or beads tightly together in rows on a cardboard, touching each other with almost no gap. Liquid model: place beads a little apart, not in straight rows, with small gaps, on a tray where they can slide. Gas model: stick a few beads far apart inside a large transparent box or on sticks at different heights, with large empty spaces. Label each model with interparticle spacing minimum, intermediate, and maximum and note the corresponding strength of attraction.
Pretend to be particles of solids, liquids, and gases, at different temperatures—create and perform a role-play/dance showing particles in motion.
Solids at room temperature: students stand shoulder to shoulder, holding hands tightly and only jiggling in place. On heating: jiggling becomes vigorous then they break handholds to walk slowly past each other in a small area representing liquid. At high temperature for gas: all let go and run freely in all directions around the room, occupying all space. At low temperature the motion slows again, showing reduced thermal energy.
Debate in the class — ‘Gases can spread and fill all the available space’. Is this property of gases beneficial or harmful?
Beneficial: This diffusion allows oxygen to reach all parts of a room for breathing, fragrance of flowers to spread, and helps uniform mixing of gases for cooking gas to mix with air for burning. Harmful: The same property lets pollutants, smoke, foul smells and leaked LPG or other toxic gases spread quickly through homes and atmosphere, causing health hazards and air pollution. Whether it is beneficial or harmful depends on which gas is spreading.