Chapter II 



— 9 — 



Structure of Water 



weight, the state of molecular accumulation occurs. As van der Waals explained the 

 difference in compressibility of gases by molecular attraction, Longinescu explains 

 molecular association in liquids by the internal compression of molecules. Thus he 

 restates Avogadro's law, "Equal volumes of fluids, and possibly solids, at the same 

 temperature and under the same external pressure, contain numbers of simple mole- 

 cules proportional to the internal pressure." Since Avogadro's law expresses the 

 molecular weight in the gaseous state by the equation 28.9d = m, Longinescu's ex- 

 pression for molecular weight in the liquid state would be lOOd = m. This would give 

 liquid water a molecular weight of 100 and a degree of molecular concentration of 5.5. 

 Though this concept is useful in consideration of molecular weight, Longinescu made 

 no attempt to explain such anomalies as the maximum density, minimum specific heat, 

 and expansion upon freezing of water. 



Modern Studies: — In 1928 Pennycuick, pointing out that oxygen 

 may display a valence of four and hydrogen of two, attributed many of the 

 anomalous properties of water to the activity of these auxiliary valence 

 forces. Assuming a tetrahedral structure for the water molecule as shown 

 in Figure 2, Pennycuick stated that water can attach itself to other mole- 

 cules either through its own negative electron pairs or through its positive 

 hydrogen nuclei. 



OH 

 H 



:0:H 



• • 



H 



0:H 



H 



+ 



Fig. 3. — The polar water chain. (From Pennycuick, 1928). 



The molecule being small (cf. Longinescu above) with 4 active aux- 

 iliary points of attack, its great activity is not surprising. 



To satisfy the auxiliary valences of oxygen and hydrogen, and to ex- 

 plain association Pennycuick proposed that polar chains may be formed 

 as in Figure 3. 



^- -/y ,n:^ ■ '^ 



■O- 

 H 



Fig. 4. — The hexagonal ring structure of water, 

 comparable with the crystal structure of ice. (From 

 Pennycuick, 1928). 



Furthermore these may close to form hexagonal rings as in Figure 4. 



