Bre'vlc"(" ,L , The creat variety of structures and combining ratios in intermetallic compound:; offers a challenge to bonding theories. Can the compositions and structures of these in:termetallics be correlated and explained in terms of the same principles used for chemical substances generally? For all substances it is the'electrons through their interactions with the nuclei which constitute the glue that binds atoms together and any explanation of the structures, compositions and stabilities of intermetallic' compounds must be based upon the same principies of electronic interactions that apply to all mat.erials. Valence-Bonds and Molecular-Orbitals The common app~oaches to the description of electronic bondinG are termed the molecular-orbital and valence-bond methods. 1 The molecularorbital method starts with the atoms already assembled in the molecule or solid and then the electrons are added to molecular orbitals in an aufb~l.u or building-up process patterned after the aufbau process for free atoms. The valence-bond approach starts with the eiectrons on the separated atoms, either in the ground electronic states or in low lying exci 1;ed electronic states, and the bonding is described generally in terms~6f electron-pair bonds between the nuclei of the approaching atoms. _ 2. lt has been shown that the methods become equivalent if used in full complexity. However, at a practical level of approximation, each method has serious deficiencies. The simple molecular-orbital method underestjmates and the simple valence-bond method overestimates electroncorrelation due to the coulombic repulsion of the electrons in an electron-pair bond. The molecular-orbital method has the haridicap of

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In order to assess the high-temperature vaporization behavior and equilibrium gas phase compositions over the condensed oxides of Be, Mg, Ca, Sr, Ba, B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Zn, Cd, and Hg, the relevant thermodynamic and molecular constant data have been compiled and critically evaluated. Selected values of the Gibbs energy functions of condensed and vapor phases are given in the form of equations valid over wide temperature ranges, along with the standard entropies and enthalpies of formation. These data were used to generate plots of equilibrium partial pressures of vapor species as functions of temperature for representative environmental conditions ranging from reducing to oxidizing. The calculated partial pressures and compositions agree, for the most part, with experimental results obtained under comparable conditions. Maximum vaporization rates have been calculated using the Hertz–Knudsen equation. Literature references are given.