Hello Aspirant,

In ice, a water molecule has four nearest neighbors to which it is bonded via hydrogen bonds. At normal pressure, water freezes at 0C (273.15 K) to form a crystal called ice-Ih. On being frozen at a temperature lower than -80C in the gas phase, water forms a crystal named ice-Ic, where c indicates cubic. The crystal lattice of ice-Ih is hexagonal and has a tridymite-like structure: Each O atom of the water molecules is surrounded tetrahedrally by four O atoms of the nearest neighbor molecules, located at a distance of 275 pm (2.75 A) from it. There are twelve second-nearest neighbor molecules, at a distance of 45 pm (4.50 A). The number of nearest neighbors in ice-Ih fouris much smaller than the 12 present in a hexagonal closest-packed structure. The resulting crystal has a large cavity parallel to its c axis, producing a loosely packed structure.



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