Particles can be atoms, molecules or ions. Particles behave differently in solids, liquids and gases. The particle model explains the differences between solids, liquids and gases.

Solids, liquids and gases change state when they are heated or cooled. Processes such as evaporation and boiling change the state of substances

Pressure in gases is caused by particles colliding with the walls of the container.

Learn about water in this KS3 guide.