Water expands when it freezes because of the molecular structure of water.
When water freezes, the molecules form a network of hydrogen bonds or a process called hydrogen bonding. These hydrogen bonds have a unique structure wherein two oxygen atoms and one hydrogen atom form one line.
Although the frozen water is considered as solidified, it also has a very open crystalline structure with a lot of spaces inside, making it less dense that most solids, and even some liquids such as liquid water.
It is because of this crystalline structure that after reaching its freezing point, water expands by about nine percent.
How Does Water Freeze?
As mentioned earlier, water freezes into a solidified state because of the rearranging of the water molecules from a straight line, to a three dimensional structure.
But how does it get to this point from its liquid state? When temperatures go down to at least four degrees Celsius or thirty-nine point two degrees Fahrenheit, the water molecules start moving closer towards each other. In fact are as closely packed as possible when water is at a temperature of four degrees Celsius.
More Facts About Frozen Water
The crystalline structure of ice, wherein the atoms form a three dimensional structure is called a tetrahedron. This is essentially a structure wherein the molecules of water are in a repeating arrangement of eight water molecules.
Water has a molecular weight of eighteen, which is very light and can almost be considered gas when water is at room temperature.
A recent study has found that although it is an accepted fact that freezes at zero degrees Celsisus, it is also possible for water not to freeze but just remain extremely cool when it is at a temperature of negative forty degrees Celsisus, due to the effects of electric fields on the freezing temperature on supercooled water.