States of Matter and Limitations of Models

This lesson covers states of matter and the limitations of bonding models as required by the AQA GCSE Combined Science Trilogy specification (8464), sections 4.2.1–4.2.3. You need to understand the three states of matter, state changes, and recognise the limitations of the models used to describe bonding and structure.

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The Three States of Matter

All substances can exist in three states: solid, liquid and gas. The state of a substance at a given temperature depends on the strength of the forces between its particles.

State	Arrangement	Movement	Spacing
Solid	Regular, ordered pattern	Vibrate in fixed positions	Closely packed
Liquid	Irregular, no fixed pattern	Move around each other freely	Close together but can slide
Gas	Random, no pattern	Move rapidly in all directions	Far apart

Particle Model Diagram

graph LR
    A["SOLID<br/>Particles vibrate<br/>in fixed positions<br/>Regular pattern"] -->|"Melting<br/>(energy in)"| B["LIQUID<br/>Particles move<br/>around each other<br/>Close together"]
    B -->|"Boiling / Evaporating<br/>(energy in)"| C["GAS<br/>Particles move<br/>rapidly, randomly<br/>Far apart"]
    C -->|"Condensing<br/>(energy out)"| B
    B -->|"Freezing<br/>(energy out)"| A