WHAT'S THE BIG IDEA?

Can you imagine iron gas? It is a possibility. Gases are one of the three states of matter, along with solids and liquids. Materials can exist in these three states - but we usually only see one or two. We know that iron is a hard, heavy solid metal - and can also be a runny liquid. But we see water in three different states - solid, liquid and gas.

The tiny particles of a gas are free to move in all directions

Solid water is called ice; liquid water is familiar; and there is water gas - or steam. A gas has weight, but no shape - and it fills the space around it. So steam quickly fills your bathroom.

(Actually, if you want to be absolutely correct, the stuff that fills your bathroom is water vapour - droplets of water in the air. Real steam is invisible - it's boiling hot - and you can't see this water gas.)

Gases spread into the space around them. Air freshener in a room can be smelled everywhere. Oxygen is gas. So is carbon dioxide - the bubbles in fizzy drinks.