The particle model — Science, 11–13 years
Matter is made of tiny moving particles. Their spacing and movement help explain solids, liquids, gases and changes of state.
Matter has a hidden structure
A table, a drink and the air in a room are all matter, even though they look very different. Imagine each one made from countless tiny particles: packed and vibrating in a solid, close but sliding in a liquid, and far apart and fast-moving in a gas. This model lets us explain what our eyes cannot see.
Why use invisible particles?
The problem is that matter can change shape, spread out or disappear from sight without vanishing. Water becomes vapour, and perfume travels across a room, so a picture of continuous, still material is not enough. The particle model links these observations with one simple explanation: particles keep moving and can spread out.
Heating an ice cube
At first, the water particles in an ice cube are held in a fixed pattern and only vibrate. As the cube absorbs heat, they vibrate more strongly until some can slide past one another: the ice melts into liquid water. With still more heating, particles move fast enough to escape into the air as water vapour.
Particles do not grow
A reasonable mistake is to draw particles larger when a substance is heated. Hot objects do often expand, so the drawing seems to fit what we observe. In the model, heating usually makes particles move faster or spread farther apart; the particles themselves do not swell like balloons.
Cooling, cooking and smells
This model helps explain why a cold drink keeps its shape, why steam fogs a bathroom mirror and why the smell of toast reaches another room. It is also useful in designing fridges, pressure containers and materials that must expand safely. The model explains patterns, though it is not a picture of each particle’s exact path.
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