C1.1 Particle Model

Solid particles are very close together and vibrate in a fixed position. Fixed shape and volume. When heated, the particles vibrate with a greater amplitude.

Liquid particles are very close together but they move and flow randomly past one another. Liquids have a fixed volume but can change shape and fill a container

Gas particles are far apart and move randomly in all directions. Gases change shape and volume to fill whatever container they are in. When heated, the average speed of particles increases.

‘simple sphere mode’. Forces between particles aren’t shown, we can’t figure out how strong these forces are and how much energy is needed to overcome them. Particles are not spherical. Particle collisions aren’t as simple as the model suggests. Particles aren’t solid. They don’t ‘bounce off’ each other

when particles gain or lose energy - because of heating or cooling- they overcome or submit to the forces of other particles. This causes them to change state.

The amount of energy required for substances to change state depends on whether the forces between their particles are strong or weak. Stronger forces between particles means more energy is required to overcome these forces. Substances with strong forces between particles will have high melting and boiling points. Weaker forces between particles means less energy is required to overcome these forces. Substances with weak forces between particles will have low melting and boiling points.