Work function, electronegativity, and electrochemical behaviour of metals II. Potentials of zero charge and “electrochemical” work functions

Preferred values of , work function, and Ez, potential of zero charge, for metals have been collected through a critical examination of much experimental data. It is shown, through three successive approximations, that the best relationship between the two above quantities is expressed by the equations: Ez=−4.61–0.40 α, where α=(2.10−xM)/0.6 is defined as the degree of orientation of water at the interface. xM is the effective electronegativity derived from polots ofa gainst the chemical electronegativity given by Pauling. xM=0.50 −0.29 is the experimental relationship for sp metals (including alkali and alkaline earth metals, with the exception of Ga, Zn and Al). For the last three metals the relationship is xM=0.50 −0.55 xM is to be taken as 1.5 for all transition metals. α=1 for transition metals, and α=0 for gold, on whose surface water molecules do not present any preferential orientation. The value of xM for transition metals must be regarded as a particular interaction parameter between surface and water arising from additional phenomena of chemisorption. The problem of the orientation of water at the free surface of solutions and at the interface with metals is discussed in detail. Complete lists of effective electronegativities, electrochemical work functions (derived from electrochemical considerations), and potentials of zero charge calculated for those metals for which no experimental data are available have been compiled.