Science · Class 8 · Chapter 7
Particulate Nature of Matter
Aim: Build a clear, working understanding of this chapter's key ideas, connected to real NCERT examples, worked problems, and everyday situations.
- Constituent particle — The basic unit making up a substance.
- Interparticle spaces — Empty gaps between constituent particles.
- Interparticle attraction — The force holding particles together.
- Melting point — Temperature a solid becomes a liquid.
- Boiling point — Temperature a liquid becomes vapour.
- Evaporation — Slow vapour formation below the boiling point.
- Fluids — Liquids and gases — both of which flow.
- Diffusion — Particles spreading on their own through motion.
Chapter 7 · Concept 1 of 9
What Is Matter Made Of?
- Grinding chalk again and again doesn't turn it into something new — every tiny speck is still chalk.
- Sugar never really disappears — Stirred into water, sugar vanishes from sight, but you can still taste it — proof it has broken into extremely tiny constituent particles.
Chapter 7 · Concept 2 of 9
Interparticle Attraction Decides Everything
- Constituent particles are held together by attractive forces — and even a small increase in distance sharply weakens that pull.
- Acharya Kanad's Parmanu — This ancient Indian philosopher proposed the idea of an indivisible, eternal particle — the Parmanu — in the Vaisheshika Sutras.
Chapter 7 · Concept 3 of 9
The Solid State
- Definite shape and volume — Particles are tightly packed, held by very strong attraction. They can only vibrate in place — not move past one another. Enough heat makes them vibrate free of their positions: melting.
Chapter 7 · Concept 4 of 9
The Liquid State
- Takes the shape of its container — Attraction is slightly weaker than in a solid — particles can move, but stay close together. Enough heat lets them escape as vapour: boiling.
Chapter 7 · Concept 5 of 9
The Gaseous State
- No fixed shape or volume — Particles move freely with almost no attraction between them, spreading to fill any available space. Liquids and gases both flow — together, they're called fluids.
Chapter 7 · Concept 6 of 9
Solid, Liquid, and Gas — Compared
- | Interparticle spacing | Attraction | Particle movement
- Solid — Minimum — Maximum — Vibration only
- Liquid — A little more — Slightly weaker — Move, but within a limited space
- Gas — Maximum — Minimum / negligible — Free, in all directions
Chapter 7 · Concept 7 of 9
Melting Points, Compared
- Substance | Melting point
- Ice — 0 °C
- Urea — 133 °C
- Iron — 1538 °C
Chapter 7 · Concept 8 of 9
Compressibility
- Gases compress easily — Pushing a syringe plunger reduces air's volume easily — gas particles have large empty spaces between them.
- Liquids barely compress — Water is practically incompressible — but when sugar dissolves, the final volume is less than water + sugar combined, since sugar particles fill the tiny gaps between water particles.
Chapter 7 · Concept 9 of 9
Diffusion
- Colour spreading in water — A drop of potassium permanganate spreads through water on its own, eventually turning it all uniformly pink — faster in hot water, slower in cold.
- Fragrance filling a room — A burning incense stick's smell reaches every corner because air particles are constantly moving, carrying fragrance particles with them.
Quick Recap
Check Your Understanding
- 1If you could remove every constituent particle from a chair, what would happen? (i) Nothing changes (ii) It weighs less (iii) Nothing of the chair remains.
- 2Why do gases mix easily, while solids do not?
- 3Spilled milk flows and spreads across a table, but the glass tumbler it came from keeps its shape. Justify this.