States of Matter and Internal Energy

This lesson explores the three states of matter using the particle model, explains how the arrangement and energy of particles differ between states, and introduces the concept of internal energy. These ideas underpin the entire Particle Model section of the Edexcel GCSE Combined Science specification (1SC0).

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The Three States of Matter

All substances can exist as a solid, liquid or gas. The state depends on the temperature and pressure.

Property	Solid	Liquid	Gas
Particle arrangement	Regular, closely packed	Irregular, close together	Random, far apart
Particle motion	Vibrate about fixed positions	Move around each other	Move rapidly in all directions
Spacing	Very small	Small	Very large
Forces between particles	Strong	Moderate	Very weak (almost none)
Shape	Fixed	Takes shape of container	Fills the container
Volume	Fixed	Fixed	Variable (fills container)
Can be compressed?	No (virtually)	No (virtually)	Yes — easily