Ice molecules

Fig. 20. The structure of ice Molecules numbered 8, 7, 6 are in contact with 5, while molecules 5, 4, 3, 2 arc in contact with 1. Molecules 2, 3, 4 are among the next-nearest neighbors of 5, while molecules 0, 7, 8 are among the next-nearest neighbors of 1. [Diagram taken from E. J. W. Verivey, Rec. trav. chim. 60, 893 (1941).]...

The explanation usually accepted for the anomalous behaviour of water between 0° and 4° C. is that the observed change in volume is the algebraic sum of two factors, namely, (a) normal expansion due to increased distance between the molecules in consequence of their increased energy, and (b) contraction due to depolymerisation of bulky ice molecules into denser water molecules.1... 

As a general rule, aqueous solutions arc less compressible than pure water,3 due, probably, to a reduction in the number of ice molecules m the presence of the dissolved salt. The value for sea-water at 17-5° C. is 4-36 xl0 5.4... 

Increase of pressure tends to reduce the viscosity of water at temperatures below 36° C.3 In this respect water differs from most liquids that have been examined, as these become more viscous under increased pressure. No doubt the explanation lies in the tendency of the higher pressures to reduce the percentage of bulky and viscous ice molecules. 

The irregularities in the specific heats and densities of water at various temperatures, particularly the contraction observed when water is warmed from 0° to 4° C., led Rontgen1 to suggest m 1892 that liquid water is a mixture of two sets of molecules m equilibrium, namely, ice molecules and water molecules. Thus ... 

The former were presumed to have a more complex structure but to be less dense than the latter. Hence, when water at 0° C. is warmed, the equilibrium at 0° is disturbed in the direction of left to right, some ice molecules melting to the more dense water molecules, and the contraction thereby resulting more than counteracts the normal thermal expansion of the liquid with rise of temperature. 

Whilst this theory renders the problem considerably more complex than Rontgen s binary theory, it enables explanations of a more satisfactory character to be given for the abnormalities in density, specific heat, etc. It is, further, quite in harmony with accepted views on molecular equilibria in general. If ice molecules can exist in water at the lower temperatures, there is no apparent reason why steam... 

The theory that liquid water is a mixture of polymerised water molecules, or contains dissolved ice, apparently first suggested by Rowland and by Whiting,2 was independently put forward by J. J. Thomson,3 Rontgen, and Sutherland.3 The ice molecule is supposed to be more complex than the liquid but less dense. This theory has been supported by appeal to the very abnormal properties of liquid water (high surface tension and dielectric constant, great ionising power for solutes, high b.p. as compared with expansion on... 

In general, except in ice, molecules in molecular crystals are packed together as closely as their size and shape allow. Because van der Waals forces and hydrogen bonding are generally quite weak compared with covalent and ionic bonds, molecular crystals are more easily broken apart than ionic and covalent crystals. Indeed, most molecular crystals melt at temperatures below 100°C. 

It is difficult to trace the historical development of the theory of water. One of the earliest documents attempting an explanation of some anomalous properties of water is Rontgen s (1892) article, which postulated that liquid water consists of two kinds of molecules, one of which is referred to as an ice-molecule. Rontgen himself admitted that his explanation of the properties of water, using the so-called mixture-model approach, had been known in the literature for some time, but he could not point out its originator. An interesting review of the theories of water until 1927 was presented by Chad well (1927). Most of the earlier theories were concerned with association complexes, or polymers of water molecules. There has been little discussion on the structural features of these polymers. 

There is a long history of the theory of water and aqueous solutions based on various mixture model (MM) approaches. One of the earliest documented explanations of some anomalous properties of water is due to Rontgen, who in 1892 proposed to view liquid water as consisting of two kinds of molecules, one of which he referred to as ice-molecules. The general idea of explaining the properties of water by viewing it as a mixture of species probably originated much earlier. 

The bond between Ice molecules and most substrates Is normally stronger than the Ice Itself. 

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