Page 366 - MODERN ELECTROCHEMISTRY

302 CHAPTER 3

Recall that, after the contribution of the ionic atmosphere to the potential at the
central ion was obtained, the Coulombic interaction between the central ions and the
cloud was calculated by an imaginary charging process, generally known as the
Guntelberg charging process in recognition of its originator.
In the Guntelberg charging process, the central ion i is assumed to be in a
hypothetical condition of zero charge. The rest of the ions, fully charged, are in the
positions that they would hypothetically have were the central ion charged to its normal
value i.e.,theotherionsconstituteanionicatmosphereenvelopingthecentralion
(Fig. 3.40). The ionic cloud sets up a potential at the site of the
central ion. Now, the charge of the central ion is built up (Fig. 3.40) from zero to its
final value and the work done in this process is calculated by the usual formula
for the electrostatic work of charging a sphere (see Section 3.3.1), i.e.,

Since during the charging only ions of the ith type are considered, the Guntelberg
charging process gives that part of the chemical potential due to electrostatic interac-
tions.
Now, the Guntelberg charging process was suggested several years after Debye
and Hückel made their theoretical calculation of the activity coefficient. These authors

Fig. 3.40. The Guntelberg charg-
ing process.