The three states
Matter can exist in three states: solid, liquid and gas. The state depends on how the tiny particles are arranged and how much they move. The same substance can change from one state to another, for example ice (solid) melts to water (liquid) and boils to water vapour (gas).
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Takes shape of container | Fills container |
| Volume | Fixed | Fixed | Not fixed |
| Particles | Close, orderly | Close, less orderly | Far apart, random |
Key idea
In a solid particles are packed tightly and only vibrate. In a liquid particles are close but can slide past each other. In a gas particles are far apart and move quickly in all directions.
Changes of state
Heating gives particles more energy so they move more and spread apart. Cooling removes energy so particles slow down and move closer. These lead to changes of state:
- Melting: solid → liquid (e.g. ice → water)
- Boiling / evaporation: liquid → gas (e.g. water → water vapour)
- Condensation: gas → liquid (e.g. water vapour → water droplets)
- Freezing: liquid → solid (e.g. water → ice)
Example
At sea level, ice melts at 0 °C and water boils at 100 °C. When you leave a wet cloth in the sun, the water evaporates and the cloth dries.
Remember
- Three states: solid, liquid, gas.
- Solids have fixed shape and volume; liquids have fixed volume only; gases have neither.
- Heating and cooling cause changes of state.
- Water melts at 0 °C and boils at 100 °C.