NCERT Solutions for Class 8 Science Chapter 7 – Particulate Nature of Matter

Have you ever wondered why ice melts into water, or why you can smell a burning stick of camphor from across the room? The answer lies in the Particle Nature of Matter. This fundamental concept of chemistry explains that everything around us—from the chair you sit on to the air you breathe—is made up of incredibly tiny particles.

NCERT Solutions for Class 8 Science Chapter 7 – Particulate Nature of Matter help students understand that all matter is made up of tiny particles that are constantly in motion. This chapter introduces the foundational concept of matter at the microscopic level.

Chapter 7 explains the characteristics of particles of matter, such as their small size, continuous motion, and attraction between them.

1.0NCERT Solutions for Class 8 Science Chapter 7 PDF Download

This blog will give you information based on the NCERT Curriculum , so you can see the behaviour of the particles that make up the three states of matter.

It's been prepared by ALLEN's expert faculty, and gives you detailed solutions, correct answers and thorough coverage of the Class 8 Science, Chapter 7 NCERT Solutions PDF based on the above-mentioned content.

2.0NCERT Questions with Solutions Class 8 Science Chapter 7 Detailed Solutions

1. 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.

Sol. (iv) closely packed in solids and move past each other in liquids.

In solids, the particles are tightly packed with very little interparticle space and strong forces of attraction. They cannot move freely but only vibrate about fixed positions, which is why solids have a definite shape and volume.

In liquids, the particles are also close together but the forces of attraction are weaker compared to solids. Thus, the particles can slide and move past each other, allowing liquids to flow, have a definite volume but no definite shape.

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.
(v) When we heat camphor in one corner of a room, the fragrance reaches all corners of the room.
(vi) On heating, we are adding energy to the camphor, and the energy is released as a smell.

Sol.

(i) True → Ice (solid) changes to water (liquid) on melting, so this is a solid-to-liquid transformation.
(ii) True → During melting, particles gain energy and their intermolecular attractions weaken, allowing them to move more freely.
(iii) True → Solids have a fixed shape and fixed volume due to tightly packed particles.
(iv) True → Solids have very strong interparticle forces and very little interparticle space, which makes them rigid.
(v) True → Camphor undergoes sublimation (solid → gas), and the vapour particles diffuse rapidly through air, spreading the fragrance to all parts of the room.
(vi) False → On heating camphor, energy is supplied to overcome intermolecular forces and convert it into vapour. The vapour diffuses and carries the smell. The smell is not released energy, but the result of gaseous camphor particles spreading in the air.

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.

Sol. (iii) Nothing of the chair will remain.

Matter is made up of constituent particles (atoms and molecules).

• A chair exists only because these particles are present, closely packed, and arranged in a definite structure.
• If all particles are removed, there would be no matter left — hence, the chair would completely disappear.
• Option (i) is wrong because without particles, there can be no structure.
• Option (ii) is wrong because it’s not about losing some particles (which would reduce weight), but about losing all particles, which means the chair ceases to exist.

4. Why do gases mix easily, while solids do not?

Sol. In gases, particles are separated by large interparticle spaces and have very weak forces of attraction. They move randomly and at high speeds, so when two gases come together, their particles intermingle quickly — this is called diffusion.

Whereas in solids, particles are closely packed and held by strong forces of attraction. They can only vibrate about fixed positions and cannot move freely. Hence, solids cannot diffuse into one another under ordinary conditions.

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.

Sol. In milk (liquid), particles are close together but not fixed in position. They can slide past each other, which allows milk to flow and take the shape of any container or surface it is on.

That is why milk spreads out on the table when spilled.

Whereas in glass tumbler (solid), particles are tightly packed with very strong forces of attraction. The particles can only vibrate about fixed positions and cannot move freely. This gives the tumbler a definite shape and definite volume, so it does not change shape like the milk.

6. Represent diagrammatically the changes in the arrangement of particles as ice melts and transforms into water vapour.

Sol.

Ice (solid) → closely packed, fixed positions.
Water (liquid) → still close but able to move/slide past one another.
Water vapour (gas) → very far apart, moving freely in all directions.

In ice, strong interparticle forces keep the molecules tightly packed in an orderly pattern.

On melting, heat energy weakens these forces, so molecules become mobile while remaining close → liquid state.

On further heating to vapour, particles gain enough energy to overcome intermolecular forces, move far apart, and spread randomly in all directions → gaseous state.

7. Draw a picture representing particles present in the following:

(i) Aluminium foil
(ii) Glycerin
(iii) Methane gas

Sol.

8. Figure ‘a’ 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 figure ‘b’ showing the arrangement of particles.

Sol.

• Solid wax on the candle → matches tightly packed particles.
• Molten wax (liquid) dripping on the sides → matches closely packed but mobile particles.
• Wax vapour/smoke (gas) rising after extinguishing → matches widely spaced particles.

In solid wax, particles are tightly packed with strong forces of attraction, giving the candle its definite shape.

On burning, part of the wax melts to form a liquid; here, the particles are still close but can slide past one another, so molten wax drips down.

When the candle is extinguished, some wax vaporizes, and the gaseous wax particles spread far apart and move randomly in air, seen as smoke.

9. Why does the water in the ocean taste salty, even though the salt is not visible? Explain.

Sol. Ocean water tastes salty because it contains a large amount of dissolved salts, mainly sodium chloride. These salts are not visible because the salt dissolves completely in water and breaks down into invisible particles. That is why we cannot see the salt, but we can taste its salty flavour.

10. Grains of rice and rice flour take the shape of the container when placed in different jars. Are they solids or liquids? Explain.

Sol. They are solids, not liquids. Rice grains and rice flour are made of solid particles with fixed shape and volume. They only appear to take the container’s shape because particles move and settle freely. Liquids, however, truly lack fixed shape and flow as a continuous fluid.

3.0Key Topics Covered in Class 8 Science Chapter 7 – Particulate Nature of Matter

• The Building Blocks: Atoms and Molecules (Constituent particles of Matter). If an item like a chair were to be stripped of its constituent particles, Matter ceases to exist).
• States of Matter:
• • Solids: Particles are very densely packed with little free space and strong attraction that limit the movement to vibrate only
  • Liquids: The particles are located close to one another; however, they can slide around each other; therefore, Liquids will flow in the shape of the container
  • Gases: Particles of this type, gas, have a large distance between each other and have very weak attraction to one another and therefore have random, highly energetic motion.
• Phase Changes: Melting (Solid to Liquid); a melting process occurs when the constituent particles gain energy and thus have a lower attraction to each other, and sublimation (Solid to Gas) occurs (Ex. Camphor) directly from a solid toa  vapour without passing through liquid.
• Diffusion: When two or more Types of Matter are mixed together. For example, gases diffuse quickly because the particles have high speeds and there are large gaps in between them.

4.0Quick Insights About the Chapter – Particulate Nature of Matter

• The Camphor Mystery: When camphor is heated, the fragrance spreads not because "energy" is released as a smell, but because gaseous camphor particles diffuse rapidly through the air.
• Invisible Salt: Ocean water tastes salty even though you can't see the salt because sodium chloride breaks down into invisible particles that dissolve completely between water molecules.
• The "Flowing" Solid: While grains of rice or flour might seem to take the shape of a jar, they are still solids. Each individual grain has a fixed shape and volume; they only appear to take the container's shape because they are small enough to move and settle freely.
• Candle Arrangement: A burning candle demonstrates all three states: solid wax provides the shape, molten wax acts as a liquid with sliding particles, and smoke represents the gaseous state with widely spaced particles