Relations between the heats of formation of lanthanide trihalides and the electronegativities of the halogen ions

Abstract

The heats of formation of lanthanide trihalides - Δ H xxx 289 may be expressed empirically in terms of the electronegativities χ A of the halogen ions ▪ where a and h are empirical constants and the factor 3, e. r C and r A represent the valence of the cation, the electronic charge, the cation radius and the anion radius, respectively. The value of ne 2/ r (C and /or A) corresponds to the electrostatic energy arising between the effective nuclear charge of the ion ne and an electron at a distance from its nucleus equal to its ionic radius r (C and /or A). The empirical constants a and b correlate with the sum of the first, second and third ionization potentials of the lanthanides giving three different trends; La-Eu(0-6 f) series. Gd-Yb(7-13 f) series and Lu(14 f) series. This means that some other factors (e.g. polarizability of the ion) affect the heat of formation.