States of Matter, Explained
Everything you can touch, pour or breathe — your desk, a glass of water, the air in the room — is matter. Matter is built from particles far too small to see, and the particle model explains solids, liquids and gases as nothing more than different ways those particles can be arranged and moving.
Picture a crowded room
It helps to imagine particles as people in a room:
- Solid — everyone stands shoulder to shoulder in fixed rows, only shuffling on the spot. Nobody can push past anyone else, so the whole crowd holds its shape.
- Liquid — people are still close together, but they can squeeze past one another and drift around. The crowd can flow into whatever shape the room is.
- Gas — people are scattered, moving fast in every direction, bouncing off the walls. They spread out to fill the entire space available.
That's the whole model: same particles, three different arrangements and speeds.
Changing state means changing energy
Nothing is added or removed when a substance changes state — only heat energy. Add energy and particles move faster and spread out further; remove it and they slow down and pack in closer.
- Melting — solid → liquid (energy added)
- Freezing — liquid → solid (energy removed)
- Evaporating / boiling — liquid → gas (energy added)
- Condensing — gas → liquid (energy removed)
An ice cube melting isn't creating new water — the same particles are simply moving faster and breaking free of their fixed positions.
Why this model matters
The particle model isn't just for describing states — it's the reasoning tool behind why solids hold their shape, why liquids find their own level, and why a smell spreads across a room. Anywhere you see matter behaving a certain way, the explanation traces back to how its particles are arranged and how much energy they have.
In short
- All matter is made of tiny particles; solids, liquids and gases are just different arrangements and speeds of the same particles.
- Solid: packed and fixed. Liquid: close but able to flow. Gas: spread out and fast.
- Adding or removing heat energy drives every change of state — melting, freezing, evaporating, condensing.
More Science guides
- Newton's Laws of Motion, Explained
A clear guide to inertia, F = ma, and action-reaction, for WA Year 10 Science students.
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