States of matter
Matter is made up of small particles called atoms. Atoms can exist on their own or together as molecules. Atoms are very small and around 100,000,000 of them end to end would measure one centimetre.
Solids, liquids and gases
The kinetic theory is an attempt to explain why materials occur in three different forms, or states. The particles in solids, liquids and gases are arranged differently and move in different ways.
The table below summarises the arrangement and movement of the particles in solids, liquids and gases and shows simple diagrams for the arrangement of the particles.
The theory can be used to explain the different properties of solids, liquids and gases.
| State | Property | Explanation |
|---|---|---|
| Solids | Have a shape and do not flow | The particles only vibrate around a fixed point and do not move from place to place |
| Cannot be squashed | The particles are touching | |
| Liquids | Flow and adopt the shape of the container | The particles can roll over each other because the bonds between them are not strong enough to keep them in a fixed position |
| Cannot be squashed | The particles are touching | |
| Gases | Spread out to fill their container | The particles are moving quickly in all directions |
| Can be squashed | There are large spaces between the particles |
Adding heat energy to particles either raises the temperature and they move faster, or bonds are broken to change from solid to liquid (melting) or liquid to gas (boiling). If a gas is allowed to cool, particles slow down and bonds reform to make a liquid (condensing) and if the liquid cools enough it turns to a solid (freezing).
Limitations of the particle theory - Higher
Particles are hard round spheres like marbles that do not make and break new bonds when they touch. We have to imagine these bonds forming and breaking even though we would not see this when using marbles to show the difference between solids, liquids and gases.