The Particle Model and States of Matter

Everything is made up of tiny particles. The state of a material depends on the strength of the forces of attraction between its particles.

When looking at objects around us, we can see that different objects are in different states of matter. Particle theory explains the unique properties of different states of matter.

There are three states of matter: solidsliquids and gases. Let’s look at how particles are arranged in each state of matter, as well as their properties.


The image below shows the arrangement of particles in a solid.

Due to the strong forces of attraction between the particles in a solid, they are very close together, arranged in a regular lattice structure.

Solids keep a fixed shape, so the particles are unable to move around. When heated, the particles vibrate more, but remain in their fixed positions.


  • Ice cubes are in a solid state


The image below shows the arrangement of particles in a liquid.

Liquid particles are arranged in random positions. This is because the forces between them are weak. However, some of the particles are still close together.

Liquids take the shape of their container, as they are able to flow. The liquid particles are always in random motion. Similar to solids, when heated, the particles vibrate more.


  • Water is in a liquid state


The image below shows the arrangement of particles in a gas.

Gas particles have very weak forces between them, so they are able to move around freely. The particles are very far apart from each other.

Gases can always take the shape of containers because they have no definite shape. When heated, gas particles move faster.


  • Water vapour is in a gaseous state

Gas Pressure

Gas pressure occurs when gas particles within a contained area are constantly moving and colliding with the surfaces of that area. The more often the particles hit the surfaces and the faster they are moving during these collisions, the higher the pressure within the contained area. This increases the pressure within the container.

This is particularly noticeable when the temperature increases, as hotter gas particles move faster, thereby increasing pressure.