# The Particle Model

### States of Matter

Solids (s), liquids (l) and gases (g) can be represented using particle diagrams. In these diagrams, particles are represented by solid spheres. Aqueous solutions are represented as (aq).

Particles in solids have less energy than liquids, which in turn have less energy than gases. To get from a solid to a liquid, or a gas, energy has to be supplied - usually through heating. During these changes the particles gain energy, which is used to break or overcome the intermolecular forces of attraction.

The amount of energy required to change state depends on the strength of the intermolecular forces between the particles of each substance. Some of the forces need to be broken during melting, whereas all of the forces must be broken during evaporating/boiling. Changing from one state to another is a physical change.

### Properties

Solids have a fixed volume and shape, and cannot flow as the particles are unable to move. They cannot be compressed as the particles are already too close together - with no space to be able to move into.

Liquids have a fixed volume, but no fixed shape, and can flow as the particles are able to move. They are able to take the shape of their container, however are unable to be compressed as their particles are already too close together, with no space to move into.

Gases do not have fixed volume, or fixed shape, and can flow as the particles are able to move. They are able to take the shape of their container, and can be compressed as their particles are far apart and have space to move into.

Higher Tier

Limitations of the simple model above include that in the model:

• there are no forces of attraction between particles
• all particles are represented as spheres
• the spheres are inelastic solids
Solids Liquids Gases
particles are very close particles are close particles are far apart
particles are arranged in a regular pattern particles are randomly arranged particles are randomly arranged
particles vibrate around a fixed position particles are able to move around each other particles move quickly in all directions
particles have low energy particles have more energy than solids particles have more energy than liquids