Matter And the Particle Model
Every question in this unit is doing the same job in disguise: it gives you something you can measure — a volume change under pressure, a density value, a temperature that won't budge while heating continues, a smoke particle jittering under a microscope — and asks you to explain it using particle spacing, particle motion and the forces between particles. Learn to read data tables this way and the whole unit stops being separate facts and becomes one repeated argument.
Overview — the particle model as one repeated argument
All matter — the copper block, the water and the air trapped in a syringe — is built from particles that never stop moving. What actually differs between solid, liquid and gas is just three things: how close the particles are packed, how strongly they pull on each other, and how much energy they have to move around. Every worked example in this unit is really asking you to link one of those three things to a real observation.
- Solid: particles locked in fixed positions, vibrating on the spot — strong forces, minimal spacing, fixed shape and volume.
- Liquid: particles still close together but free to slide past one another — fixed volume, no fixed shape.
- Gas: particles far apart with negligible forces between them, moving fast and randomly in every direction — no fixed shape or volume.
- The examiners' favourite move: give you raw numbers (density, % volume change, spacing) and make YOU work out the state. 'Gases are compressible' memorised alone never scores full marks — you must use the numbers given.
The shape of the chapter
Command term guidance
| Command term | What it demands | AO | Mark-earning move |
|---|---|---|---|
| Deduce | Reach a conclusion using information given — must use specific numbers/observations from the question. | Data analysis | No mark for the correct conclusion alone; the cited figure earns the mark. |
| Explain | Give reasons using cause-and-effect language linking observation to particle behaviour. | Application | Mark is for the causal link ('because... therefore...'), not for restating the fact. |
| Describe | State what is observed/true in detail, no reasons required. | Knowledge | Extra reasoning doesn't lose marks here but won't add any either. |
| Justify | Give evidence-based reasons that support a specific stated claim. | Analysis | Must reference the exact claim in the question, not general theory. |
| Evaluate | Weigh strengths and limitations to reach a balanced judgement. | Evaluation | One-sided answers (only benefits or only drawbacks) cap at half marks. |
| Compare | Give similarities AND differences between two or more things. | Analysis | Listing features of each separately with no direct link between them loses marks. |
| Distinguish | State the difference(s) between two similar concepts. | Analysis | Two separate definitions with no explicit point of difference scores zero. |
Key point
Overview