ABSTRACT
Water (H2O) is a fascinating substance and has many properties that make it unique. It is, for example, the only chemical on earth that is naturally found as a solid, a liquid and a gas. It is the only material that expands when it is cooled and contracts on melting. As its temperature lowers, ice starts to form and at about 4C, its volume starts to increase. It is 9 per cent bigger by the time it becomes solid ice. This increase is due to the molecules rearranging themselves into rigid structures, more widely spaced than before. If this did not happen, ice would be denser than water and sink to the bottom of the oceans. This would cause northern lakes and seas to freeze solid. Without this property all the creatures living in the water would die.
