Chapter II 



11 



Structure of Water 



temperature brings about wider spacing of the attractive centers. The 

 minimum volume shown at 4° C. results from alternate predominance of 

 these effects. The latent heat of fusion is not unexpectedly high ; it repre- 

 sents only the separation and not the destruction of ring structure. Evapora- 

 tion breaks all the intermolecular bonds ; as high as three-fifths of the latent 

 heat of vaporization has been ascribed to the dissociation of the complex 

 molecules. Water is unusual in its solvent power because the solute is held 

 in solution by its auxiliary valence forces that the solvent is able to neu- 

 tralize. Since a solute will first be attacked by the more active unassociated 

 molecules, the effect of solution is to reduce the number of such molecules 

 with a corresponding shift in equilibrium and a decrease in association. The 

 lowering of the temperature of the maximum density of water and the 

 decrease in compressibility upon addition of a solute may be explained on 

 this basis. The predominance of compounds containing six and twelve 

 molecules of water of crystallization results from incorporation of hexa- 

 hydrol in crystals. The self -ionization of water is explained by occasional 

 breaks as indicated in Figure 5. 



The high dielectric constant of water is pictured as resulting from the 

 short-time displacement of a hydrogen nucleus under the influence of the 

 field due to a lone oxygen electron pair as rupture of a polar chain occurs. 

 The abnormal velocities of hydrogen and hydroxyl ions are related to the 

 possible addition of water at the active end and loss at the inactive end of 

 each ion under the influence of an applied E.M.F. Thus by applying the 

 principles of molecular structure and crystal structure to water, many of 

 the abnormal or anomalous properties may be explained. He fails to ex- 

 plain the reason for polymers that would act as solute molecules. The 

 formation of such stable groups in contrast to the tendency toward lattice 

 formation is difficult to visualize. 



Fig. 6. — Electronic distribution in the simple water mole- 

 cule. (From Bernal and Fowler, 1933). 



X-Ray Analysis : — Analysis by x-rays has become an invaluable tool 

 in the hands of the scientist. It has been used in the attack on the struc- 

 ture of water. Chadwell (1927) points out the discrepancies in the 



