Relations between the heats of formation of the alkali chalcogenides and the electronegativities of the chalcogen ions (O, S, Se and Te)

Abstract

The heats of formation of M 2X chalcogenides (M = Li, Na, K, Rb and Cs; X = O, S, Se and Te), - ΔH 298 XXX, may be expressed empirically in terms of the electronegativities X A of the chalcogen ions ▪ where a and b are empirical constants and −2, e, r c and r A represent the valence of the anion, the electronic charge, the cation radius and the anion radius, respectively. The values of e 2 r C and − 2 e 2 r A correspond to the electrostatic energy arising between the effective nuclear charge of the M + and/or X 2− ion and an electron at a distance from the nucleus equal to the ionic radius r C and /or r A Although its physical meaning is not clear, this empirical equation is useful in predicting the heat of formation. The heats of formation of Rb 2Te(solid) and K 2Te(solid) are estimated as −87 and −89 kca1 (th) mol −1, respectively.