CC1.1 — States of matter (Edexcel 1SC0)
Particle model
All matter consists of tiny particles. The three states of matter differ in how particles are arranged and how much energy they have.
| State | Arrangement | Motion | Energy |
|---|---|---|---|
| Solid | Regular lattice; close together | Vibrate around fixed positions | Low |
| Liquid | Random; close together | Move around each other | Medium |
| Gas | Random; far apart | Move rapidly in all directions | High |
Changes of state
- Melting (solid → liquid): particles gain energy; overcome lattice forces.
- Boiling (liquid → gas): particles gain enough energy to escape liquid surface.
- Freezing (liquid → solid): particles lose energy.
- Condensation (gas → liquid): particles lose energy.
- Sublimation (solid → gas directly): e.g. iodine, dry ice (CO₂).
Changes of state are physical changes — no new substances are formed; the change is reversible.
Limitations of the particle model
The particle model treats particles as solid spheres with no forces between them — useful but simplified. In reality, particles have intermolecular forces and are not rigid spheres.
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