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Particulate Nature of Matter – Class 8 Science notes, important questions and MCQs

NCERT Class 8 Science, chapter 7. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Matter is made of tiny particles that have spaces between them, attract each other and are always moving. Their arrangement explains solids, liquids and gases.

Particles

Particles are very small and have gaps between them (sugar dissolves and "disappears" into water).
Particles attract each other; the attraction is strongest in solids and weakest in gases.
Particles keep moving; motion increases with temperature (diffusion is faster in hot water).

States of matter

Solid: fixed shape and volume, particles tightly packed.
Liquid: fixed volume, takes the shape of the container.
Gas: no fixed shape or volume, highly compressible.
Melting, boiling, condensation and freezing change states by adding or removing heat.

Key terms

Diffusion: mixing of particles of different substances on their own
Melting point: temperature at which a solid becomes liquid
Boiling point: temperature at which a liquid becomes gas throughout

Formulas

Water: melting point 0 °C, boiling point 100 °C (at normal pressure)

Important questions with answers

Why can we smell food cooking in the kitchen from another room?2 marks

Particles of the smell mix with air particles and spread (diffuse) quickly through the air to other rooms.

Compare solids, liquids and gases in terms of arrangement of particles and spaces between them.3 marks

Solids: particles closely packed in fixed positions, very small spaces, strong attraction. Liquids: particles close but can slide, small spaces, moderate attraction. Gases: particles far apart, large spaces, very weak attraction, move freely.

Explain melting, boiling, evaporation and condensation in terms of particles, and why evaporation causes cooling.5 marks

On heating a solid, particles vibrate faster and break free from fixed positions: melting (at the melting point). In a liquid, at the boiling point particles throughout gain enough energy to escape as gas: boiling. At any temperature, the fastest particles at the surface escape: evaporation. On cooling a gas, particles slow down and come close to form a liquid: condensation. Evaporation cools because the particles that escape carry away energy, so the average energy of the remaining liquid falls (sweating cools the body).

Quick revision

Particles have spaces, attract and move.
Diffusion is fastest in gases.
Heat changes state.

Exam tips

Gases can be compressed because of large spaces between particles (LPG, CNG cylinders).
Smell of food spreads due to diffusion of gas particles.

Practice MCQs

Which state has a fixed shape?
1. solid
2. liquid
3. gas
4. all
Show answer
Answer: (a) solid. Solid.
Water boils at
1. 0 °C
2. 50 °C
3. 100 °C
4. 37 °C
Show answer
Answer: (c) 100 °C. At normal pressure.
The smell of incense spreads in a room because of
1. condensation
2. melting
3. diffusion
4. freezing
Show answer
Answer: (c) diffusion. Particles move and mix.
Gases are easily compressed because
1. particles have large spaces between them
2. particles are heavy
3. particles do not move
4. they are coloured
Show answer
Answer: (a) particles have large spaces between them. Large spaces.
Diffusion is fastest in
1. gases
2. liquids
3. solids
4. all equal
Show answer
Answer: (a) gases. Gas particles move most freely.
Diffusion is faster in hot water than cold water because
1. particles move faster at higher temperature
2. hot water is heavier
3. cold water has no particles
4. sugar melts
Show answer
Answer: (a) particles move faster at higher temperature. More kinetic energy.
The force of attraction between particles is the greatest in
1. gases
2. liquids
3. all equal
4. solids
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Answer: (d) solids. Tightly held.
Ice floats on water because
1. it is a solid
2. it is colder
3. it is less dense than water
4. it has air bubbles only
Show answer
Answer: (c) it is less dense than water. Water expands on freezing.

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Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.