Why does water expand when frozen?
Unlike most other substances, water expands when it freezes. This is due to its unique molecular structure, where one oxygen atom bonds with two hydrogen atoms. The larger oxygen atom moves to one side of the molecule while the hydrogen atoms move to the opposite side, giving water molecules a distinctive, bent structure. When water freezes, the molecules become more ordered and arrange themselves in a hexagonal, crystal configuration that increases the space between the molecules. “Because water has this funny bent structure, those atoms pack most efficiently in a crystal structure,” says physics professor Stephen Morris of the University of Toronto.
