7.6 Going Deeper: Enrichment & Exam Preparation

Particles in Everyday Life

You’ve Met These Particles Already Sugar vanishing into tea, salt making the sea taste salty though you can’t see it, the smell of cooking drifting through the house, a balloon you can squeeze, soap lifting grease — every one is the particulate nature of matter in action. Once you picture the tiny moving particles, dozens of everyday puzzles solve themselves.

Quick Reference: The Three States

Property Solid Liquid Gas
Interparticle spacing Minimum A little more Maximum
Packing Closely packed Loosely packed Free
Interparticle attraction Maximum Slightly weaker Negligible
Particle movement Only vibrate Within a limited space Freely, everywhere
Shape Fixed Takes container’s shape Fills the container
Volume Fixed Fixed Not fixed
Compressible? No Practically no Yes

Memory Tricks & One-Page Revision

Revision Card

  • Matter = tiny particles + spaces between them + attractions holding them.
  • Solid → Liquid → Gas: attraction decreases, spacing increases, freedom increases. Heat drives it.
  • Shape/volume: Solid (fixed/fixed) · Liquid (no shape/fixed volume) · Gas (no shape/no volume).
  • Melting point = solid→liquid; boiling point = liquid→gas. Evaporation = slow, surface-only, at any temperature.
  • Gases compress (lots of space); liquids/solids don’t.
  • Diffusion = particles spreading on their own; faster when hotter.
  • Liquids + gases = fluids (they flow).
  • The building-block particles are really atoms and molecules (more in higher grades).

Spot the Mistake

Find the Flaw

  1. “Melting increases the interparticle attractions.” — False: melting weakens attractions, letting particles move apart.
  2. “Liquids have no fixed shape and no fixed volume.” — Half wrong: liquids have no fixed shape but do have a fixed volume; it’s gases that have neither.
  3. “Sugar disappears when it dissolves, so it is destroyed.” — False: it breaks into particles that fit into the spaces between water particles — still there (you can taste it).

A Step Further: Atoms and Molecules

What the Particles Really Are The tiny particles of matter are atoms and molecules. Iron is made of iron atoms, gold of gold atoms. Some atoms can’t exist alone — they join up into molecules: two hydrogen atoms make a hydrogen molecule, and a water molecule is two hydrogen atoms plus one oxygen atom. You’ll explore atoms and molecules in the next chapter and in higher grades.

Test Your Reflexes

A quick-fire drill: a clue appears. Which state of matter does it point to — Solid, Liquid or Gas? Build a streak!

Which state of matter?
Pick the state the clue describes.
Score 0 · Streak 0

Exam Corner: CBSE-Style Practice

Mixed Practice (objective, short, long, HOTS)

Objective type (1 mark each)

  1. The basic units that make up a larger piece of a substance are called its ______ particles.
  2. The gaps between the particles of matter are called ______ spaces.
  3. The state of matter with the weakest (negligible) interparticle attraction is the ______.

Short answer (2 marks each)

  1. Why do liquids have a fixed volume but no fixed shape?
  2. Why is a gas easily compressed but a liquid is not?

Long answer (3 marks each)

  1. Compare solids, liquids and gases in terms of interparticle spacing, attraction and particle movement.
  2. Explain, using particles, why a drop of potassium permanganate colours a whole glass of water — and why it spreads faster in hot water.

HOTS (Higher Order Thinking)

  1. Sugar and sand are both solids, yet sugar dissolves in water and sand does not. Explain in terms of particles.
  2. Grains of rice and rice flour take the shape of any jar they are poured into. Does that make them a liquid? Explain.

Assertion–Reason (Choose: (a) both true, R explains A; (b) both true, R doesn’t explain A; (c) A true, R false; (d) A false, R true.)

  1. Assertion (A): A gas can be compressed much more than a liquid.   Reason (R): Gas particles have much larger spaces between them than liquid particles.
  1. constituent particles.
  2. interparticle spaces.
  3. gas (gaseous state).
  4. In a liquid the particles are held together closely enough to keep a fixed volume, but the attractions are weak enough that they can move around, so the liquid flows and takes the shape of its container — hence no fixed shape.
  5. A gas has large spaces between its particles, so pressure can push them closer (compress it). A liquid’s particles are already close together with little space, so it is practically incompressible.
  6. Spacing: least in solids, more in liquids, most in gases. Attraction: strongest in solids, weaker in liquids, negligible in gases. Movement: solids only vibrate, liquid particles move in a limited space, gas particles move freely everywhere.
  7. Water particles are in constant motion: they pull permanganate particles off the grain and knock them throughout the water until the colour is uniform (diffusion). In hot water the particles move faster, so the colour spreads faster.
  8. Sugar’s particles are held by attractions weak enough for water to pull them apart and slot them into the spaces between water particles, so it dissolves. Sand’s particles are held by stronger attractions that water cannot break, so they stay together and settle — sand is insoluble.
  9. No — they are solids (each tiny grain keeps its own fixed shape and volume). A heap of small solid grains flows and fills a jar, but that is many solids shifting, not a true liquid.
  10. (a) — Both true and R explains A: the larger interparticle spaces in a gas are exactly why it can be compressed far more than a liquid.

Glossary

Key Terms

  • Constituent particle: the basic unit making up a piece of a substance.
  • Interparticle space: the gap between neighbouring particles.
  • Interparticle attraction: the attractive force holding particles together.
  • Melting point / boiling point: the temperatures for solid→liquid / liquid→gas.
  • Evaporation: slow, surface-only change of liquid to vapour at any temperature.
  • Diffusion: the spontaneous spreading and mixing of particles.
  • Fluid: a substance that flows (a liquid or a gas).
  • Atom / molecule: the actual tiny particles that make up matter.