Cambridge IGCSE Chemistry

## Solids, liquids and gases All matter is made of particles, and which state a substance is in depends on how those particles are arranged and how they move. The three states differ in what they do to shape and volume, and each difference follows from the particle picture. | Property | Solid | Liquid | Gas | |---|---|---|---| | Shape | Fixed | Takes the shape of the container | Fills the container | | Volume | Fixed | Fixed | Not fixed | | Compressible | No | No | Yes | | Particle separation | Very close together | Close together | Far apart | | Particle arrangement | Regular, in fixed positions | Irregular, in a random jumble | Irregular, random | | Particle motion | Vibrate about fixed positions | Slide past one another | Move quickly in straight lines in all directions | A solid keeps its shape because its particles cannot leave their positions, and a liquid flows because its particles are free to move past each other while still touching. A gas can be squashed into a smaller volume because most of the space between its particles is empty, whereas a solid or liquid has almost no spare space to lose. ## Changes of state Heating a solid gives its particles more energy, so they vibrate harder until they break free of their fixed positions and the solid **melts**. A liquid **boils** when it is heated to its boiling point and particles escape from throughout the liquid as bubbles of vapour. **Evaporation** is different: it happens only at the surface and at any temperature…