Water behaves differently than almost all other liquids because it expands when it is frozen. As a liquid is cooled down the molecules move more slowly allowing the attractive forces between them to become stronger. Eventually, these forces become strong enough to hold the molecules in a fixed position (they can still vibrate but not change their relative positions) and the liquid becomes a solid. The molecules in the solid have reached an optimum 'closeness' to each other and the solid usually has a very ordered arrangement of molecules in what is known as a crystal lattice. …
