Water is a compound of two chemical elements: hydrogen and oxygen. A water molecule is made up of two hydrogen atoms bonded to an oxygen atom. The formula for water is H₂O.
Molecules are always in motion. The movement and distribution of the molecules are what determines the substance’s state of matter.
- In the liquid state, water molecules move around freely, sliding and jostling against each other like dancers in a crowded room.
- In solid ice, the water molecules slow down and are stacked in a crystal lattice pattern, like oranges packed neatly in a crate.
- In the gas state, the water molecules are far apart and zoom around at the speed of flying bullets. The gas expands to fill whatever space is available.