# Describe the differences in the arrangement and movement of particles in a solid compared to a gas, and use the particle model to explain why a gas can be compressed but a solid cannot.

> OCR GCSE Chemistry A: Gateway Science (J248) — C1.1 The particle model · Describe · 4 marks

> A bicycle pump contains air that can be squeezed into a smaller volume when the handle is pushed in. However, the metal cylinder of the pump itself cannot be squeezed in the same way.

## Mark scheme (4 marks)

1. In a solid, particles are held in a regular arrangement; in a gas, particles are relatively spread out / randomly arranged.
2. Particles in a solid have the least energy and vibrate about fixed positions; particles in a gas move randomly in all directions with the most energy.
3. A gas can be compressed because there are large spaces / gaps between the particles, so the particles can be pushed closer together.
4. A solid cannot be compressed because the particles are already close together / there are no significant gaps between particles.

## Key terms

- [particle model](https://www.gradenine.co.uk/glossary/particle-model)
- [solid](https://www.gradenine.co.uk/glossary/solid)
- [gas](https://www.gradenine.co.uk/glossary/gas)
- [compressed](https://www.gradenine.co.uk/glossary/compressed)
- [arrangement](https://www.gradenine.co.uk/glossary/arrangement)

## Related

- [Revision notes for OCR GCSE Chemistry A: Gateway Science (J248)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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