Solids, liquids and gases

The particle theory of matter is a model that describes the arrangement and movement of particles in a substance. The model is used to explain the physical properties of solids, liquids and gases.

Particle arrangement and movement

Table showing diagrams of solid, liquid and gas, their particle arrangements, movement and closeness.

The particles in the diagrams could be atoms, molecules or ions depending on the type of substance, eg ionic compounds, simple molecules, giant covalent structures, and metals.

Explaining properties

Solids:

  • have a fixed volume and a fixed shape
  • cannot flow, because their particles cannot move from place to place
  • cannot be easily compressed, because their particles are close together with no space to move into

Liquids:

  • have a fixed volume but no fixed shape
  • can flow and take the shape of their container, because their particles can move around each other
  • cannot be easily compressed, because their particles are close together with no space to move into

Gases:

  • have no fixed shape or volume
  • can flow and completely fill their container, because their particles move quickly in all directions
  • can be compressed, because their particles are far apart with space to move into