Why does water expand when it's frozen?

Liquids expand when the molecules move with more energy.Liquids usually contract on cooling.The force of attraction between them causes the molecule to move slower.When they freeze, they contract more to form a rigid solid structure.That is not the case with water.Instead of contracting, it expands.

The water molecule, consisting of 2 atoms of hydrogen and one of oxygen, forms a Mickey Mouse head-like structure in which the ears are the hydrogen atoms and the head is represented by the oxygen atom.There is a slight positive charge on the hydrogen atoms side of the molecule.The water is drawn towards each other.The molecule set themselves in an arrangement that is very open in nature and contains more space than the water in the liquid state.Water expands on freezing and becomes less dense.It contracts on thaw, unlike most other liquids.

The normal behavior of water when it is cooling up to 4 C is to expand in volume.The molecule starts to get into a hexagonal lattice structure.There is a lot of intermolecular space in this structure.The expansion is what it is.When it is finally frozen to ice, the same applies.

It is not.Other substances include plutonium and germanium.

Water bottles crack on freezing of the water inside because of this phenomenon.The floating of ice cubes in water is an effect of this.It is because ice is less dense than water.