Solids, liquids and gases

The Earth, its atmosphere and the oceans are made from substances in different states. The particle model describes the arrangement, movement and energy of particles in a substance. The model explains the physical properties of substances in the solid, liquid and gas state.

Particle arrangement and movement

Table showing diagrams of solid, liquid and gas, their particle arrangements, movement and closeness.

The particles in the diagrams could be atoms, molecules or ions, depending on the type of substance.

Explaining physical properties

Solids:

  • have a fixed shape and cannot flow, because their particles cannot move from place to place
  • cannot be compressed, because their particles are close together and have no space to move into

Liquids

  • flow and take the shape of their container, because their particles can move around each other
  • cannot be compressed, because their particles are close together and have no space to move into

Gases:

  • flow and completely fill their container, because their particles can move quickly in all directions
  • can be compressed, because their particles are far apart and have space to move into

curriculum-key-fact
Individual particles do not have the same properties as the bulk substance. The physical properties are due to the arrangement and movement of all the particles.

Question

Use the particle model to explain why an iceberg has a fixed shape.

An iceberg is in the solid state. It has a fixed shape because the particles (water molecules) are arranged in fixed positions.

Question

Use the particle model to explain why water from a river can change shape when filling a container.

Water is in the liquid state. It can flow because its particles can change position and slide past each other.

Question

Use the particle model to explain why air can fill a room.

Air is in the gas state. It fills a room because the particles are far apart and are free to move position.