Particulate Nature of Matter
Everything around us — solids, liquids and gases — is made of extremely tiny particles. This Class 8 Curiosity chapter gathers the evidence that matter is particulate: particles are very small, have spaces between them, move constantly, and attract one another. These ideas explain diffusion, the three states of matter, and what happens when we heat or cool a substance.
Learning objectives
- State that matter is made of tiny particles with spaces between them.
- Explain diffusion using the motion of particles.
- Describe solids, liquids and gases by particle arrangement.
- Relate temperature changes to particle motion and changes of state.
Key concepts
Matter is made of particles
Matter is made of very tiny particles, far too small to see. When sugar dissolves in water it seems to vanish but still sweetens the water, showing it has broken into particles small enough to fit between the water particles. A few crystals of potassium permanganate can colour a large volume of water, hinting at how numerous and tiny the particles are.
Particles have space and keep moving
There are spaces between particles, and the particles are in constant motion. The spreading of the smell of incense across a room, or a drop of ink colouring still water on its own, is diffusion — the mixing of particles of two kinds because of their movement. Diffusion is faster in gases than in liquids.
Three states of matter
In solids, particles are tightly packed in fixed positions with strong forces, so solids keep a fixed shape and volume. In liquids, particles are close but can slide past one another, so liquids flow and take the shape of the container while keeping their volume. In gases, particles are far apart and move freely, so gases fill any container completely.
Effect of temperature
Heating gives particles more energy, so they move faster and the spaces between them usually increase, which is why substances expand on heating. Enough heating lets particles overcome their forces of attraction, so a solid melts to a liquid and a liquid boils to a gas; cooling reverses these changes.
Key definitions
- Matter
- Anything that has mass and occupies space, made up of tiny particles.
- Diffusion
- The spreading and mixing of particles of one substance among those of another due to their motion.
- States of matter
- The three common forms — solid, liquid and gas — that differ in particle arrangement.
- Melting
- The change of a solid into a liquid on heating.
Solved examples
Q1. Why does the smell of food spread across the whole house?
Solution: The food's particles are constantly moving and diffuse through the air, mixing with air particles until they reach our nose.
Q2. Why does a gas fill its container completely but a solid does not?
Solution: Gas particles are far apart and move freely, spreading to fill all space; a solid's particles are fixed in place, so it keeps a definite shape.
Q3. Why does a balloon expand a little when left in the sun?
Solution: Heat makes the gas particles move faster and spread out, increasing the spaces between them, so the gas expands.
Common mistakes to avoid
- Thinking dissolved sugar is destroyed — it only breaks into particles too small to see.
- Believing there is nothing (not even space) between particles.
- Saying liquids have a fixed shape — they have fixed volume but take the container's shape.
- Assuming particles stop moving; they move at all temperatures, just more slowly when cold.
Particulate Nature of Matter — MCQ Quiz
10 questions with instant feedback. Use number keys 1–4 to answer.
Matter is made up of:
Practice questions
Short answer
Give one piece of evidence that matter is made of particles.
A few crystals of potassium permanganate colour a large amount of water, showing matter is made of countless tiny particles.
Why is diffusion faster in gases than in liquids?
Gas particles are farther apart and move much faster and more freely than liquid particles.
How do particles in a solid differ from those in a gas?
Solid particles are closely packed in fixed positions; gas particles are far apart and move freely.
Long answer
Describe the arrangement and movement of particles in the three states of matter.
In solids, particles are tightly packed in fixed positions with strong forces of attraction, so solids have a fixed shape and volume and only vibrate in place. In liquids, particles are close together but can slide over one another, giving a fixed volume but no fixed shape. In gases, particles are far apart with very weak forces and move rapidly in all directions, so gases have neither fixed shape nor fixed volume and fill their container.
Explain, using particles, why substances expand on heating and can change state.
Heating supplies energy that makes particles move faster, so the spaces between them increase and the substance expands. With enough heat the particles gain sufficient energy to overcome their forces of attraction: a solid's particles break free of their fixed positions and it melts to a liquid, and on further heating the liquid's particles escape into the air as a gas (boiling). Cooling removes energy and reverses these changes.
HOTS (Higher Order Thinking)
Two gas jars, one with a coloured gas, are placed mouth to mouth and opened. What happens and why?
The colour spreads into both jars because gas particles are in constant motion and diffuse into one another until evenly mixed.
Why can we walk through air easily but not through a wall?
Air is a gas with particles far apart and weak forces, so we push through easily; a wall is a solid with closely packed particles held by strong forces, which resist being pushed apart.
Quick revision
Revision notes
- Matter = tiny particles with spaces between them, always moving.
- Diffusion: mixing due to particle motion; fastest in gases.
- Solid (fixed shape/volume) → liquid (fixed volume) → gas (neither).
- Heating: faster particles, more spacing, expansion and change of state.
Key takeaways
- Particle spacing and motion explain the three states of matter.
- Diffusion is direct evidence that particles move.
- Temperature changes particle energy, causing expansion and state changes.
Frequently asked questions
What is the particulate nature of matter?
The idea that all matter is made of tiny, constantly moving particles with spaces between them.
What is diffusion?
The spreading and mixing of one substance's particles among another's because the particles move.
Why do solids have a fixed shape?
Their particles are closely packed in fixed positions by strong forces of attraction.