The electrostatic entropy of solvation of an ion, ΔS°e, or the contribution to ΔS°e from the co-ordination sphere of the ion, ΔSI, II, have been shown to be quantitative measures of the structure-making and structure-breaking effects of ions of the alkali halide series in water and in non-aqueous solvents. Both entropy criteria indicate that in water the ions Li+, Na+, Ag+ and F- are net structure-makers, the ions Rb+, Cs+, Cl-, Br-, I- and ClO4- are structure-breakers, and K+ is a borderline case. In the non-aqueous solvents formamide, methanol, N-methylformamide, dimethylformamide, dimethylsulphoxide and acetonitrile, all the above ions are structure-makers with the exceptions of the weak structure-breaking ion ClO4- in formamide and the borderline cases of ClO4- in methanol and I- in formamide. It is shown that the ΔS°e or ΔS°I, II values may be used to assign single-ion B- or B′-coefficients and that for water and several non-aqueous solvents there are good linear correlations between the entropy values and the single-ion coefficients. There are also good linear correlations between the entropy values and single-ion V̄° values when the latter are based on V̄° (H+, aq, 1 mol dm-3) = -5.4 cm3 mol-1 and when values of V̄° in non-aqueous solvents are assigned by the correspondence method. It is further shown that the general conclusions reached do not depend on any particular choice of ionic radii, although the Goldschmidt-Pauling set is preferred, and it is suggested that the derived ΔS°e and ΔS°I, II values are close to 'absolute' values and hence provide an 'absolute' measure of ion-solvent interactions.
|Number of pages||15|
|Journal||Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases|
|Publication status||Published - Dec 1 1982|
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