• Solid - Solids have a definite size and shape. Particles are close together, and vibrate.
• Liquid - Liquids do not have a fixed shape. Particles take the shape of their container. Particles are further apart, and can move freely.
• Gas - Gases do not have a fixed shape. Particles take the shape of their container. Particles are far apart, and move very freely.

CHANGES OF STATE

• Melting - the change of state from solid to liquid
• Freezing or Solidification - the change of state from liquid to solid
• Boiling or Evaporation - the change of state from liquid to gas
• Condensation - the change of state from gas to liquid
• Sublimation - the change of state directly from gas to solid, and vice versa (e.g. of carbon dioxide gas or carbon dioxide solid 'dry ice')

MELTING AND BOILING POINTS

• Melting Point - the temperature at which matter changes from solid to liquid, and vice versa (e.g. The melting point of water from ice to liquid water is 0^oC.)
• Boiling Point - the temperature at which matter changes from a liquid to a gas, and vice versa (e.g. The boiling point of water from liquid water to steam is 100^oC.)