Solids, liquids and gases
Chemistry · Key Stage 2 · The School
Three ways matter behaves
A SOLID keeps its shape (ice cube, spoon). A LIQUID flows and takes the shape of its container but keeps its volume (water, milk). A GAS spreads out to fill whatever space it can find (steam, air). Same stuff, different behaviour.
Heating and cooling change state
Heat ice and it MELTS to water; cool water and it FREEZES back to ice (at 0°C). Heat water enough and it EVAPORATES into water vapour; cool the vapour and it CONDENSES back to liquid — that is the mist on a cold window. The material is the same water throughout.
The water cycle
The sun evaporates water from seas and lakes. The vapour rises, cools, and condenses into clouds. Drops grow heavy and fall as rain, which runs back to the sea — and the loop begins again. The planet has been recycling the same water this way for billions of years.
Put a slightly soft football on a sensitive balance: 410 g. Pump 30 more pumps of air into it and weigh again: 412 g. The extra 2 g is the air you added, which proves gas has mass. The ball did not get bigger by much, so what changed is how many particles are inside the same space — and that squeeze is exactly why the ball is now hard.