Ice lattice structure. Molecular model of one of the several structures of ice, the frozen form of water. The crystalline lattice structure of ice explains why it is a hard, brittle solid. Here the six-fold hexagonal symmetry (known as Ih) explains the hexagonal symmetry of snowflakes. The atoms are shown as red spheres. There are two hydrogen atoms and one oxygen atom making up each water molecule. The bonds between the central oxygen atom and the two hydrogen atoms either side are light grey rods. The dark grey rods are the hydrogen bonds formed between the oxygen atom in one molecule and a hydrogen atom in a neighbouring molecule. The structure at right is the same as the one at left, but seen from a different angle.