Caption：Water molecules in ice form an open hexagonal lattice in which every water molecule is hydrogen bonded to four others. The geometric regularity of these hydrogen bonds contributes to the strength of the ice crystal. The hydrogen bonding pattern of water is more irregular than that of ice. The absolute structure of liquid water has not been determined.
Notes：All hydrogen bonds are satisfied in ice. The structure of ice at 0o is less dense than that of liquid water at 0o due to its open lattice.