ELECTRONEGATIVITY AS A FACTOR OF STABILIZATION OF VALENCE STATES IN COMPLEX OXIDES OF p- AND d-ELEMENTS

From the thermodynamic standpoint, the stability of valence states in binary and complex oxides of d- and p-metals is considered by the change in the free Gibbs energy in the oxidation-reduction reactions. The presence of a correlation between a valence state of a metal and the electronegativity of its oxide has been established. Thus, metals in the lowest valence state M(II) – (Mn(II), Fe(II), Tl(I), Pb(II)) have low (less than 1.5 еV1/2/O2-) values of electronegativity and reveal predominantly basic properties. Their oxides are undergone to oxidation reactions with increasing valence states of M(III) or M(IV) and, accordingly, electronegativities with conversion to amphoteric oxides. The essence of the stabilization of the lowest state is the binding of binary oxides of metals in complex oxide compounds (oxosalts), and the stabilization can be represented as the difference between the electronegativities of oxides. It is established that with a certain difference of electronegativities the stabilization of the valence state increases significantly, and in some cases complete stability is realized. The motive force of the process of stabilization of the lower valence state is the increase of the ionicity of the bond in the complex oxide compared to the binary oxide. Instead, metal oxides in the highest valence states (M(IV), M(VI)) have high (above 2 еV1/2/O2-) values of electronegativities and exhibit mainly acidic properties. Under reducing conditions, they undergo reduction to lower valence states (M(III), (M(IV)), again acquiring amphoteric properties to form complex oxide compounds with higher oxides. Although the stability values of the valence states of these oxides are quite high at normal amphoteric pressure, their further stabilization is possible. The essence of the process, as in the previous part, is to increase the ionicity of the bonds between the low-valent metal and polyhedron, and most importantly – to increase the covalence of the high-valent metal-oxygen bonds in the latter. It should be noted that the stabilization effect in this case also depends on the difference between the electronegativities of the oxides – basic and stabilizing. Thus, using data from the electronegativities of metal oxides, which show the instability of a valence state, it is possible to effectively carry out the processes of their stabilization.