Solid A solid has a fixed volume and shape. Two examples of a solid are shown below.

Metal Wood

This is an example of how atoms are arranged in a solid

Liquid A liquid has a fixed volume but no fixed shape. It will take the shape of the container it is in.

Milk Ice cubes

This is an example of how atoms are arranged in a liquid

Gas No fixed shape or volume. The gas will spread to fill the volume and shape of the container.

Bromine Gas in a jar. Fluorine gas in a jar.

This is an example of how atoms are arranged in a gas

Melting This is when a solid melts and changes into a liquid.

For example, a chocolate bar melting into liquid chocolate on a hot sunny day

Heat from the sun

Freezing This is when a liquid freezes and changes into a solid

For example, when water is put into ice cube trays in the freezer. It turns into a solid, ice.

Put tray in freezer Water freezes.

Water Ice

Condensation This is when a gas changes into a liquid.

For example the steam from a shower ( gas ) changes into condensation on a mirror. ( water/ liquid )

Steam Water on Mirror ( Condensation )

Evaporation This is when a liquid changes into a gas.

For example, water in a kettle that changes into steam when the kettle boils.

Water in Kettle Steam from kettle

Particles Everything is made up from particles. The particles are too small to see without the use of a powerful microscope.

The simplest particles are called atoms. Atoms are the simplest particles known from which everything is made.

When 2 or more atoms join together they form a

molecule

Diffusion

This is when one type of particles moves through another type of particles. Diffusion will only take place when the particles are in a liquid or gas state.

Diffusion can not take place in solids. This is because they are not free to move.

The above diagram is an example of perfume fumes spreading through the air. The perfume fumes will slowly leave the bottle and start to spread through the air. Eventually allowing us to smell the perfume with our nose. This example is a perfume gas diffusing through the air (gas).

The above example is of a coloured ink (liquid) diffusing through water (liquid). At first the ink particles are all together but they will slowly spread out (diffuse)

Diffusion:

Is fastest in a gas as the particles are moving faster, i.e. have more energy and are more spread out.

Is slower in a liquid as particles are closer and aren't moving as fast.

It doesn't occur in solids as particles are held in position.

Expansion

Solids, liquids and gases expand (take up more room) when heated.

Expansion in a solid shown below

Heat

This is due to the particles moving faster and further apart as they gain more energy. Expansion in a solid requires most energy, while expansion in a gas requires least energy.

Contraction

When cooled, solids, liquids and gases contract (take up less room) as particles move closer.

Cooling

A bimetallic strip is made from two strips of different metals joined together.

A bimetallic strip bends when heated since one metal expands ( particles move apart ) more than the other.

Some fire alarms and thermostats use bimetallic strips.