Eli5: Materials expand when heated and contracts when cooled. So why does water expand when it freezes instead of contracting?

Question

Eli5: Materials expand when heated and contracts when cooled. So why does water expand when it freezes instead of contracting?

In: 24

Answer 1

Correct, most materials do expand when heated and cool when contracted. So does water: https://www.e-education.psu.edu/earth111/node/842 Water has a maximum density (lowest volume) around 4 degrees C.

Ice (well, the most common kind you find in ordinary pressures) has a hexagonal crystal structure that occupies more volume than liquid water. Basically the molecules can squish together tighter if they’re liquid. https://en.wikipedia.org/wiki/Ice_Ih

They form hexagons because hexagons are bestagons, but more because water molecules are boomerang shaped.