Bond formation in electrosorbates—I correlation between the electrosorption valency and pauling's electronegativity for aqueous solutions

the electrosorption valency, γ, which can be determined experimentally, is discussed in dependence on system-specific parameters. For correlation purposes, values at the potential of zero charge, ?N, and small coverages, θ ≈ 0·1, only are used, and mixed adsorption and phase formation must be excluded. Experimental data for 50 ionic systems in aqueous solutions are summarized. For homonucleus ions, a simple correlation between the ratio, γ/z, and the electronegativity difference, |χ_M?χS|, is established. This relationship can be described using a reasonable assumption on the geometric factor, g, and Pauling's formula for the charge transfer in diatomic molecules. It follows from this simple model as well as from the experimental data that covalent adsorption (γ/z ≈ 1, ? λ/z ≈ 1), takes place in the range, |Δχ| < 0·5, but ionic adsorption (γ/z < 0·2, λ ≈ 0) occurs at |Δχ| > 1·0. For 0·5 < |Δχ| < 1·0 the partial charge transfer (0 < ?λ/z < 1) with the formation of polarized bonds is important.Heteronucleus ions are discussed qualitatively. The influence of the geometric factor seems to be dominant for these ions.