A discussion on the energies involved in specific adsorption of ions

The change in specific adsorption of I^? ions on the series of metals Au, Hg, Bi, Pb, Cd, and Ga is analyzed using data of specifically adsorbed charge and shift in potential of zero charge. Factors determining the change in adsorbability are discussed in the light of previous formulations. It is shown that the work connected with water desorption as an ion becomes adsorbed, usually neglected or underestimated in previous discussions, is very likely to be the main factor determining the change in adsorbability along the series of metals. A rough estimation of energies involved in water desorption suggests that metal—water surface bonds are probably weak on sp-metals so that they are unable to affect the reactivity of metal surfaces with respect to the gas phase as strong covalent surface bonds are involved, for instance in the hydrogen evolution reaction. Conversely, the strong effect of water desorption on the specific adsorption of ions may be an indication of ion—metal interactions to be substantially independent of the nature of the metal. This suggests that covalent contributions to the surface bond are apparently minor for metals more electropositive than Au.