IGCSE Physics / Solids, liquids and gases

Particles in solids, liquids and gases

Edexcel International GCSE Physics (4PH1), chapter 19: Solids, liquids and gases, specification point 5.10P. Free lesson.

Read the revision notes · IGCSE Physics past papers

The arrangement and movement of particles explain the properties of solids, liquids and gases. Use these ideas to describe each state and draw its particle diagram.

How particle arrangement and movement differ

Each state is described by its arrangement and motion. These differences explain how the state behaves. In a solid, particles are close packed in a regular pattern. They vibrate about fixed positions. In a liquid, particles are close together and touching, but randomly arranged. They slide past each other. In a gas, particles are far apart and randomly arranged. They move quickly and randomly in all directions.

How particles explain shape, density and squashing

Particle motion explains shape. Particle spacing helps explain density and whether a substance can be squashed. A solid keeps a fixed shape because its particles vibrate in place and cannot swap positions. A liquid flows to fit its container because its particles can slide past each other. A gas spreads out to fill its container because its particles move freely in all directions. Solid and liquid particles are close together, so both are difficult to squash. Gas particles are far apart, leaving space to push them closer together. Gas has low density because its particles are…

How to draw a liquid particle diagram

Liquid particles are often drawn with gaps by mistake. They are about as close together as solid particles. What changes is their arrangement and movement. Draw particles touching in a random jumble, filling the bottom of the container. The particles can slide past each other, so they do not stay in a regular pattern. Particles in a heated liquid move faster on average. They also collide with the container walls.

Why solid particles still move

Solid particles do not travel from place to place, but they are not still. They vibrate about fixed positions, so they still have kinetic energy. Particles in a solid cannot swap places. They keep vibrating on the spot.

Answering questions about particle models

Use precise descriptions of spacing, arrangement and movement. Link the spacing to how easily particles can be pushed closer together.

More lessons in Solids, liquids and gases