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122 CHAPTER 2

for the case where the solvation number and the coordination number is the same (SN
= CN), and

when the solvation number differs from the coordination number (SN CN). The
is the energy of one H bond, equal to –21 kJ The numerical values are
listed in Table 2.17.

2.15.11.6. (Model B). This model (Table 2.16) considers the
structure-breaking region as consisting of dimers, which are formed from monomers
from liquid water. If the lowering in the potential energy due to formation of a dimer
from two monomers is then

where is the number of molecules in the SB region per ion, and is taken as
the energy of one H bond, i.e., –21 kJ Values of (model B) are listed in
Table 2.17.

2.15.11.7. (Model C). In this model (Table 2.16) the SB region is
considered to consist basically of monomers. Some of these monomers are H bonded
to the molecules in the first shell. The SCW and NSCW participate in two and three
H bonds with molecules in the SB region. The formation of an SB region of monomers
can be treated according to the cycle shown in Fig. 2.39. Therefore, one can write

or

or

clearly cannot be taken as the heat of evaporation for liquid water. It
may be possible to get some rough value for it. In some theories of liquids, a property
of interest is that of the free volume, that is, the volume occupied by the liquid minus
the volume of the actual molecules considered to occupy “cells.” One such theory
gives