Everything is made of moving particles

Ice, water and steam are the same molecules. What changes is how fast they move and how tightly they hold on to each other.

In the box below are a few hundred atoms that attract each other when they are close and push apart when they touch. The heater under the box sets the temperature: warmer means the atoms jiggle faster on average.

Colours show what each atom is doing right now:

• pale blue — 8 or more close neighbours, packed like a crystal;
• blue — 3 to 7 neighbours, crowded but loose, like a liquid;
• orange — fewer than 3, flying alone, like a gas.