Model Calculations of the Thermochernical Properties of Gaseous Metal Halides

Two semiempir ical models for est imating the thermochemical propert ies of gaseous metal halides, the Rittner electrostatic model and the ionicity-corrected Birge-Sponer extrapolation, are reviewed, and the areas of appl ica-bi l i ty of the models are discussed. Possibil it ies for application of the Rittner model to metal mono-, di-, and tr ihal ide systems are i l lustrated by examples from the I IA and I I IB metals, and extension to the lanthanide hal ide series is explored. Over-al l, the Rittner model appears to have much promise as a tool for estimating thermochemical data, but proper usage demands that due con-sideration be given to the inherent l imitations of the model. A simple ionicity correction removes much of the uncertainty associated with dissociation en-ergies derived from the l inear Birge-Sponer extrapolation, providing another usefu l tool for estimating thermochemical data. Our knowledge of the thermochemical propert ies of metal hal ide systems is still far from complete, makin