Particle Theory 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. Particle Theory explains the unique properties of the 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.

Solids

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 begin to vibrate in their fixed positions.

Example

  • Ice cubes are in a solid state

Liquids

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 randomly moving.

Similar to solids, when heated, the particles vibrate more.

Example

  • Water is in a liquid state

Gases

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

Example

  • Water vapour is in a gaseous state

Comparing the States of Matter

Below is a table that compares the three states of matter.

StateSolidLiquidGas
Arrangement of particlesRegular arrangementRandom arrangementRandom arrangement
Movement of particlesVibrate slowly around a fixed positionVibrate quickly and particles are free to move around each otherMove quickly in random directions
Closeness of particlesVery close togetherSomewhat close together, but without a regular arrangementFar apart

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