Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!

KS3 Bitesize

Science

Particle model

You can use the idea of particles to explain the properties of solids, liquids and gases.The strength of bonds between particles is different in all three states. It explains why solids cannot flow, and why gases can be compressed.

Introduction

This Revision Bite covers:

Solids

Steel, plastic and wood are solids at room temperature. Ice is solid water.

The particles in a solid have the following characteristics:

  • they are close together

  • they are arranged in a regular pattern

  • they are held together by strong forces called bonds

  • they can vibrate in a fixed position

  • they cannot move from place to place

In order to see this content you need to have both Javascript enabled and Flash installed.

The table shows some of the properties of solids and why they are like this.

Property of solids Why they are like this
They have a fixed shape and cannot flow. The particles cannot move from place to place.
They cannot be compressed or squashed. The particles are close together and have no space to move into.

Liquids

Mercury, lemonade and water are liquids at room temperature.

The particles in a liquid are:

  • close together

  • arranged in a random way

The particles in a liquid can:

  • move around each other

The bonds in a liquid are strong enough to keep the particles close together, but weak enough to let them move around each other.

The table shows some of the properties of liquids and why they are like this.

Property of liquids Why they are like this
They flow and take the shape of their container. The particles can move around each other.
They cannot be compressed or squashed. The particles are close together and have no space to move into.

In order to see this content you need to have both Javascript enabled and Flash installed.

Gases

Air, helium and chlorine are gases at room temperature. Water vapour is water as a gas.

The particles in a gas are:

  • far apart

  • arranged in a random way

The particles in a gas can:

  • move quickly in all directions

There are no bonds between the particles in a gas, so they are free to move in any direction.

In order to see this content you need to have both Javascript enabled and Flash installed.

The table shows some of the properties of gases and why they are like this.

Property of gases Why they are like this
They flow and completely fill their container. The particles can move quickly in all directions.
They can be compressed or squashed. The particles are far apart and have space to move into.

Flowing

Liquids and gases do not have a fixed shape. They can flow and fill their containers, but solids cannot. The particle model explains why.

Solids

Solids cannot flow because their particles are only able to vibrate and cannot move from place to place.

Liquids

Liquids can flow because their particles can move over each other. When water is poured into a glass, the particles of water move over each other and into the corners of the glass. The particles keep on moving over each other as the water takes the shape of the glass. The animation shows how this works.

In order to see this content you need to have both Javascript enabled and Flash installed.

Gases

Gases can flow because their particles can move in all directions. When a Bunsen burner is connected to a gas tap and turned on, natural gas flows through the rubber tubing. The particles of natural gas are free to move anywhere inside the tubing, and pressure forces them through the tubing into the Bunsen burner.

Arrangement and movement

The table summarises the arrangement and movement of the particles in solids, liquids and gases. It also shows simple diagrams of the arrangement of the particles that you should be able to draw and recognise.

  Solid Liquid Gas
Arrangement of particles

Close together

Regular pattern

Close together

Random arrangement

Far apart

Random arrangement

Movement of particles Vibrate on the spot Move around each other Move quickly in all directions
Diagram Solid particles are close together in a regular patten Liquid particles are close together in a random pattern and can move around each other. Gas particles are far apart in a random pattern, and can move freely and quickly

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.