Ion Solvation The Born Equation

Consider a spherical ion of radius a which carries a central electrical charge q. The work required to increase this charge by dq is the potential energy 

The solvent polarity function F(D) = (1 — 1 /D) having the same saturation property as the Debye and Onsager functions. As D goes to infinity all three functions approach the limit of 1. 

1 Solvatochromic Shifts of Ions. There is at the present time no theory of the solvatochromic shifts of ions except for the effect of the change of volume in different electronic states. This follows from the Born equation, and a being the ionic radii in states i and f (initial and final). 

The Born equation is based on the simple model of a spherical ion with a single charge at its centre. Such an ion has no dipole moment and no higher multipole moments, but real molecular ions are of course much more complex. Since the electrical charge is distributed among all the atoms of the 

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