The density of ice is lower than that of water, meaning that for the same amount of water, ice will have a greater volume than liquid water.
This is a special characteristic unique to water, that its liquid form is denser than both its solid and gaseous forms. This lowering of density occurs because the molecular bonds in water (dihydrogen monoxide) are hydrogen bonds, and the crystal structure formed when freezing the molecules into a solid cause the atoms to distance themselves from each other, resulting in expansion.
