Water evaporating. Image 3 of 3. Artwork of water molecules evaporating from ice. The atoms are shown as balls here, and are colour coded: oxygen (red) and hydrogen (yellow). Water has the formula H2O, with each oxygen atom bonded to two hydrogen atoms. In the gaseous state, the molecules are widely and randomly spaced. Evaporation occurs when a substance turns into a gas below its boiling point. For water as a solid (ice) and as a liquid, see images A504/087 and A504/088 respectively.