Oscillations, Waves, and Interactions - GWDG

Multistep association of cations and anions 351
Figure 15. Sketch of preferential orientation of dipolar solvent molecules in the Coulombic
field of small cations.
apparently irrotationally bound solvent molecules per cation or anion, respectively.
For aqueous solutions the Z + values of some mono-, bi-, and trivalent cations [21]
are collected in Fig. 17 where the diameter of dielectrically saturated water shells,
relative to the ion diameter, is also shown graphically.
Among the monovalent ions only lithium and sodium induce a noticeable effect of
dielectric saturation. With the alkaline earth metal ions saturation corresponds with
roughly six completely irrotationally bound water molecules per cation and with
trivalent main group aluminium, yttrium, and lanthanium ions twelve to thirteen
water molecules per cation apparently do not contribute to the static permittivity of
Figure 16. Permittivity ratio ɛ(0)/ɛv(0) as a function of volume fraction v of salt for
solutions of LiCl in water (• [77], ɛv(0) = ɛw(0) = 78.35 ± 0.05 [46]) and in methanol (◦
[78], ɛv(0) = 32.64 ± 0.20 [46]) at 25 ◦ C. The dashed line represents the mixture relation
(Eq. (16)).