The Particle Model of Matter

The particle model is a scientific model that explains the behaviour of matter using four ideas:

1. All matter is made of extremely small particles.
2. There are spaces between the particles.
3. The particles are always moving, and they move faster when the substance is hotter.
4. There are forces of attraction between the particles, pulling them towards one another.

The three states are simply three settings of the same four ideas:

A model is not a photograph — nobody has ever seen these particles with an ordinary microscope. A model earns its place by explaining and predicting, and this one does both remarkably well.

Worked example — explaining diffusion. Someone opens a bottle of vinegar in the kitchen and two minutes later you smell it in the lounge. Explain using the particle model.

1. The vinegar evaporates: some particles escape from the liquid into the air.
2. Gas particles move fast and in all directions (idea 3).
3. There are large empty spaces between air particles (idea 2), so the vinegar particles can spread through them.
4. They spread out until they are evenly mixed through the room. This spreading is called diffusion.

Prediction the model makes: warm the room and the smell arrives sooner, because hotter particles move faster. Try it — the model is right.