Chemistry

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

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

Property of solidsWhy 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.

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 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 liquidsWhy 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.

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.

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

Property of gasesWhy 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.

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.

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.

SolidLiquidGas Arrangement of particles

Regular pattern

Random arrangement

Random arrangement

Movement of particles Vibrate on the spot Move around each other Move quickly in all directions Diagram

Solids, liquids and gasses have physical properties. The way they behave is affected by heating and cooling. We will also look at pressure and diffusion in gases.

Materials expanding and contracting can also cause problems. For example, bridges expand in the summer heat and need special joints to stop them bending out of shape.