The Particle Model and Its Limitations

This lesson covers how the particle model is used to explain the properties of the three states of matter, but also why the model has important limitations, as required by the Edexcel GCSE Chemistry specification (1CH0, Topic 1). You also need to be able to predict the state of a substance from melting and boiling point data, and understand how simple and giant structures affect melting points.

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Using the Particle Model to Explain Properties

The particle model represents particles as small, solid spheres. Despite its simplicity, it is remarkably useful for explaining many observations.

Why Gases Are Compressible

Gas particles are far apart with large gaps between them. When pressure is applied, the particles can be forced closer together, so the volume of the gas decreases. In contrast, solid and liquid particles are already close together, so they cannot be compressed significantly.

Why Liquids Flow

In a liquid, the forces between particles are weaker than in a solid, so particles can slide past each other. This allows the liquid to flow and take the shape of its container.

Why Solids Have a Fixed Shape