The volume of most materials decreases as they freeze. But when water become ice, its volume increases. Why does the volume of water increase when...

The volume of water increases when it is frozen because the hydrogen bonds between its molecules become fixed to form a “crystalline” lattice as kinetic energy is lost.

Water is composed of two hydrogen atoms that are covalently bonded to a central oxygen atom. Water is polar. This means that there are partially positive and partially negative charges within a water molecule.  The electrons are pulled towards the oxygen more than they are the hydrogens....

The volume of water increases when it is frozen because the hydrogen bonds between its molecules become fixed to form a “crystalline” lattice as kinetic energy is lost.

Water is composed of two hydrogen atoms that are covalently bonded to a central oxygen atom. Water is polar. This means that there are partially positive and partially negative charges within a water molecule.  The electrons are pulled towards the oxygen more than they are the hydrogens. This is because the oxygen is more electronegative than the hydrogens. Thus, because electrons are negatively charged and they are pulled towards the oxygen, oxygen becomes slightly negative. Likewise, because the electrons are pulled away from the hydrogens, the hydrogens become slightly positive.

The slight charges within water molecules creates an intermolecular force between several water molecules called a hydrogen bond. The hydrogen bonds of water exist between the hydrogen of one water molecules and the oxygen of a second water molecule.

A substance freezes when its temperature decreases past its freezing point. Temperature is a reflection of the average kinetic energy amongst the molecules of a substance. Thus, when water freezes, it loses kinetic energy. Kinetic energy is the energy of movement. A decrease in kinetic energy and temperature implies that the water molecules are moving less.

As the kinetic energy of the water molecules decreases, the hydrogen bonds between water molecules become fixed. According to International Association for the Properties of Water, a lattice of water molecules forms “where each hydrogen atom is line between two oxygen atoms”. There is a lot of open space between the water molecules of the “crystalline” structure of ice. Thus, the volume of frozen water expands when it freezes.