The strength of chemical bonds in solids and liquids

Abstract

The strengths of chemical bonds between atoms are accurately measured and widely available for molecular gases, but an established method of quantifying bond strengths in liquids and solids is not available, and the strengths of these bonds are generally unknown. A new term, the condensed bond enthalpy (CBE), is proposed to specify the energy contained in bonds between atoms in condensed states. An approach to estimating these bond strengths is developed by combining classical thermodynamic concepts with measured heats of formation and crystallographic data. A nearly complete set of elemental CBE and a selection of CBE between unlike metal atom pairs are produced using the method described here. Elemental bond enthalpies generally range from about −0.1eV to −1.3eV, and bonds between unlike atoms studied here range from about −0.6eV to −1.1eV. The validity and utility of these values are demonstrated by using them to estimate enthalpies of fusion and surface energies in elemental metals and heats of formation of ternary intermetallic compounds. Predicted enthalpies are generally within experimental errors for all three comparisons. Bond enthalpies are found to have a mild but systematic dependence on chemistry and atomic structure in some of the binary systems studied here, but are essentially independent of the atomic environment in other systems. The uncertainty in εij values (±4%) is small enough to enable classical approximations, but is inadequate when higher precision is needed.