Covalency in the hydrogen bond and the properties of water and ice

Abstract

Covalency in a hydrogen bond between two water molecules produces a partial charge separation and some rehybridization of the L -shell electrons of the oxygen atom partner. These changes promote the participation of the molecules in additional bond formation which, in turn, stabilizes the original bond. These interactions must be expected to impart a co-opera­tive character to hydrogen-bond formation in liquid water, and it is postulated that the structure of this liquid is characterized by co-operatively bonded flickering clusters of ice-like material surrounded by, and alternating roles with, disordered fluid which makes up the rest of the sample. This assumption offers an explanation for a number of facts, including the essential identity of the heats of activation obtained for viscous flow, for self-diffusion, for dielectric relaxation and (probably) for bulk relaxation. It also makes possible the interpre­tation of the extra ice-likeness found in aqueous solutions of non-polar solutes, and of the further fact that this extra ice-likeness seems to be accompanied by a lengthening of dielectric relaxation time. When applied to ice these concepts, taken together with the discussion given by Jeffrey et al . (1956) of Wurzite-type crystals, seem to offer a straightforward explanation of the facts that a ‘diamond’ modification of ice is observed at low temperatures and that the c/a ratio in hexagonal ice becomes smaller with rising temperature. The degree of covalency which this explanation presupposes seems to require a modification of the simple Bjerrum (1951) picture of the rotational defects which have been invoked to explain the dielectric properties of ice. An alternative dielectric process seems to be possible which would involve flickering droplets of liquid-like material in ice, which might, mutatis mutandis , play a role corresponding to that of flickering clusters in the liquid phase.