The Particle Model and States of Matter

Everything is made up of tiny particles. The state of a material depends on how strong the forces of attraction are between the particles of the material.

When looking at objects around us, we can see that different objects are in different states of matter. The Particle Theory Model is used to explain the unique properties of the different states of matter.

There are three states of matter: Solids, Liquids and Gases. We will look at how particles are arranged in each state of matter, as well as their properties.


This diagram represents solids. As shown, the particles are very close together causing them to touch in a regular lattice shape. The particles are close together due to the strong forces between them.

Solids keep a fixed shape, meaning the particles are unable to move around.

The particles are able to vibrate during certain conditions. For example, when heated, the particles begin to vibrate in their positions.


  • Ice cubes would represent the arrangement of particles in a solid


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

Liquids take the shape of containers, as they are able to flow.

The liquid particles are always randomly moving. Similar to solids, when heated, the particles vibrate more.


  • Water would represent the arrangement of particles in a liquid


Gas particles have very weak forces between them, so they are able to move around freely. As you can see in the diagram above, the particles are very far apart from each other. Gases can always take the shape of containers because they have no definite shape.

When you increase the level of heat, gas particles move faster.


  • Water vapour can represent the arrangement of particles in a gas

Gas Pressure

This is where a gas is within a contained area, and as the particles are constantly moving, they tend to hit the surfaces of the contained 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. they are increasing their pressure. This is especially true when there is an increase in temperature because the hotter the gas gets, the faster the particles move.