Why does ice floats on water?

[Open Intelligence]

Ice is a simple molecular solid in which the lattice forces are H-bonds. The H-bonds and covalent bonds are arranged tetrahedrally around each H2O molecule. The arrangement of water molecules in ice crystals create a very open structure (the H2O molecules are not closely packed). This accounts for the fact that ice is less dense than water at OoC (zero degrees celcius).