Single ion free energies of hydration were assigned by Latimer, Pitzer, and Slansky by choosing a set of ion radii which made both negative and positive ions fall on the theoretical Born curve in a plot of ΔF against 1/r′. The r′ values were the crystal ion radii plus 0.1 A for negative ions and plus 0.85 A for positive ions. It is now shown that this assignment of single ion free energies is consistent with the single ion entropies of hydration if S̄H+ is —2.1 (the Eastman value). The ΔS values are proportional to Z/r′ and the tentative suggestion is made that it is the temperature coefficient of r′ which leads to the Z/r′ function. It is proposed that the ΔF values be used to calculate a consistent set of radii of aqueous ions which will take into account coordination numbers and polarization.

Topics
Entropy, Free energy, Thermodynamic states and processes
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E. D. Eastman as reported by
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National Bureau of Standards Selected Values of Chemical Thermodynamic Constants, Washington, D.C.
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W. M. Latimer, The Oxidation States of the Elements and Their Potentials in Aqueous Solutions (Prentice‐Hall, New York, 1952), second edition.
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L. Pauling, The Nature of the Chemical Bond (Cornell Press, Ithaca, New York, 1940), second edition.
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W. H. Zachariasen, Abstracts of the American Crystallographic Association Meeting, April, 1950.
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V. M. Goldschmidt, Skrifter Norske Videnskaps‐Akad. Oslo. I. Matemat.‐Naturv. Kl. 1926, No. 8, 69.
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© 1955 American Institute of Physics.
1955
American Institute of Physics
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