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ION–SOLVENT INTERACTIONS 39

2.3. A LOOK AT SOME APPROACHES TO SOLVATION DEVELOPED
MAINLY AFTER 1980
There are three main approaches to the study of solvation that have been developed
largely since the first edition of this book was published in 1970 (Table 2.2).

2.3.1. Statistical Mechanical Approaches

Statistical mechanical approaches apply mainly to deductions about structure and
are the basis of interpretations of the entropy of ions in solution and the solution’s heat
capacity. The entropy of a system can be calculated if the partition functions of the
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ions and the water molecules surrounding them are known. The partition functions
(translatory, rotational, and vibrational) can be obtained from textbook material by
assuming a structure of the ion–solvent complex. By comparing calculations based on
various assumptions about structure with the values obtained from experiments,
certain structures can be shown to be more likely (those giving rise to the calculations
that match the experiment), others less probable, and some so far from the experimental
values that they may be regarded as impossible.

2.3.2. What Are Monte Carlo and Molecular Dynamics Calculations?

The easy availability of computers of increasing power has greatly encouraged
the two approaches described in this section. In the Monte Carlo (MC) approach,

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Although these statistical mechanical approaches have been used increasingly in recent times, a paper by
Eley and Evans written as early as 1938 is the origin of partition functional treatments of solutions.