4. solids liquids and gases

solids

→ Have a fixed shape and fixed volume. Their particles are packed closely together and vibrate in fixed positions.

liquids

→ Have a fixed volume but no fixed shape. They take the shape of their container.

gases

→ Have no fixed shape or volume. They spread out to fill their container.

change of state

→ When a substance changes from one state of matter to another, such as solid → liquid or liquid → gas.

melting point

→ The temperature at which a solid changes into a liquid.

boiling point

→ The temperature at which a liquid changes into a gas throughout the liquid.

evaporation

→ The change from liquid to gas at the surface of a liquid, occurring below the boiling point.

condensation

→ The change from a gas to a liquid.

expansion

→ When a substance increases in size or volume, usually when it is heated.

contraction

→ When a substance decreases in size or volume, usually when it is cooled.