What is matter?
Matter is anything that has mass and occupies space (has volume). Your body, the air in the classroom, sea water and a piece of iron are all matter. Things such as light, heat and sound carry energy but have no mass, so they are not matter.
The three states
Most matter around us exists as a solid, a liquid or a gas. The kinetic theory says all matter is built from tiny particles (atoms or molecules) that are always moving. How the particles are arranged decides the state.
- Solid – particles packed closely in an orderly pattern; they only vibrate, so a solid keeps a fixed shape and fixed volume.
- Liquid – particles are still close but can slide past one another, so a liquid takes the shape of its container yet keeps a fixed volume.
- Gas – particles are far apart and move quickly in all directions, so a gas has no fixed shape and no fixed volume and can be compressed.
Key idea
The particles in every state are the same; only their spacing, arrangement and speed differ. Heating gives particles more energy and can change one state into another.
Changes of state
Adding or removing heat changes the state without making a new substance:
- Melting: solid → liquid, e.g. ice to water.
- Freezing: liquid → solid.
- Boiling / evaporation: liquid → gas.
- Condensation: gas → liquid, e.g. steam on a cold glass.
- Sublimation: solid → gas directly, e.g. dry ice or iodine.
Example
A cook in a Malaysian kitchen boils water for teh tarik: the liquid gains heat, its particles move faster, and some escape as steam (a gas). When the steam meets a cool tile it condenses back into tiny water droplets.
Remember
Mass is measured in kilograms and does not change when a substance melts or boils – the same particles are simply rearranged.