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ION–SOLVENT INTERACTIONS 71
of interionic forces, or ion-pair formation, individual ions (none associated into pairs)
can be related to the mobility of the ions, and by the equation (Section 4.4.5).
The transport number (Section 4.5.2) of the cation, is given by
and
In electrostatics, a charge q under the influence of a field X experiences a force
Xq. Here,
where is (the radius of the ion and its primary solvation shell) and this allows
one to use independent knowledge of the mobility, to obtain the radius of the moving
solvated ion (Chapter 3). One also knows the crystallographic radius of the bare ion
inside the solvation sheath, Hence:
