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ION–SOLVENT INTERACTIONS 121

where is the polarizability of the ion. Values of calculated from Eq.
(2.67) are listed in Table 2.17.
2.15.11.3. The lateral interactions in the coordination shell for a CN of
4 and 6 can be calculated. A vs. CN plot obtained for CNs of 4 and 6 can be
extrapolated. Thus, when CN 1, i.e., there is no other molecule to
interact with; and for CN = 6, the extrapolation is made to follow the shape of the curve
of vs. CN, obtained from the equation

where is a geometrical factor depending on the CN. The arises only from
the SCW. Thus, for large ions, which have a low SN, obtained from the
vs. CN plot is negligible. Therefore, for large ions has
been neglected.

2.15.11.4. This term can be determined from

Substituting in Eq. (2.69) the appropriate values for and the following
equation is obtained:

where and are in picometer (pm) units.
2.15.11.5. (Model A). This model (Table 2.16) considers H bonding
between the molecules in the first layer and those in the region of structure breaking
(SB) (Fig. 2.37). The solvated coordinated water (SCW), which is oriented toward the
ion, has two H-bonding positions blocked by the ion and offers the remaining two sites
for H bonding to the solvent molecules in the SB region (Fig. 2.37). The NSCW is still
attached predominantly to the solvent structure but on the average has an H-bonding
position blocked by the ion and thus can offer three H-bonding sites to molecules in
the SB region. Thus, the net gain in energy from H bonding between molecules in the
B region and those in the first layer will be for the SCW and
for NSCW, i.e.,