This paper discusses the calculation of internuclear distances by a soft-sphere ionic radii model for twenty crystalline Group 1 halides and hydrides and three ammonium halides with either sodium chloride or caesium chloride structures. It also describes calculation of internuclear distances with the soft-sphere model for three crystalline Group 2 fluorides with fluorite structures and fifteen Group 2 crystalline binary salts (oxides, sulfides, selenides and tellurides) with sodium chloride structures. Soft-sphere calculated radii for Group 1 salts are compared with other theoretical radii. Soft-sphere calculated results agree very well with experimental measurements in all cases except for lithium hydride. The probable reasons for the discrepancy with lithium hydride and merits of the soft sphere model are discussed. A simple expression to calculate lattice energies using the soft-sphere radii concept is given and results compared well with lattice energies calculated by the Born-Haber cycle.

Less familiar aspects of ionization energies of atoms and atomic ions from s, p, d, and f blocks of the periodic table are discussed. Apparent irregularities in the first and second ionization energies of transition metals and rare earth metals are explained in terms of electronic configurations of the ground states. A semiquantitative treatment of pairing, exchange, and orbital energies accounts for discontinuities at half-filled p, d, and f electron shells and the resulting zigzag patterns.

This paper briefly describes the many different sets of ionic and covalent radii available. A simple model of ionic and covalent bonding is proposed and an equation to calculate internuclear distances of covalent, ionic and metallic lattices is described. Derivation of covalent radii and the use of a proposed model of metallic structure and bonding to derive ionic radii are discussed. A brief summary of the development of the simple equation for calculating internuclear distances of ionic compounds is provided. Values of internuclear distances calculated from the derived radii are compared to observed values and give good agreement, showing strong evidence that ionic and covalent radii are not additive and electronegativity influences bonding and internuclear distances. Ionic radii derived from the proposed model are applied to calculate lattice energies which agree well with literature values/values calculated by the Born Haber cycle. Work functions of transition metals are shown to be simple inverse functions of the derived radii. Internuclear distances of inter-metallic compounds are calculated and compared with observed values to show good agreement. This work shows that the proposed model of metallic structure complements the band theory and expressions introduced in this work can be used to predict ionic and covalent bond lengths (in different environments) that have not yet been determined as well as being a method for resolving bond type.

No abstract

No abstract