Molecular Constants and Chemical Theories II. Additive Molecular Constants and Chemical Structures

Abstract

All additive molecular constants, besides parachor and molecular refractivities (Part I), in particular also dipole moments, bond distances, and energies of formation (or bond energies) may be separated into individual (atomic or bond) contributions according to different proposed structures of a covalent molecule or different chemical theories on which these structures are based. Such constants do not therefore possess diagnostic qualities as to the nature of different covalent bonds, and different theories or concepts based on them, by necessity are inconclusive. A number of standard examples of molecules formed by a marked central atom are considered, which often are assumed to establish the existence of a second variety of covalent linkage, i.e., coordinate bonds, or its wave mechanical counterpart, i.e., enhanced resonance of covalent and ionic (or other) forms. For all of them, all the above molecular constants are in perfect agreement also with the older classical formulae, including those of pentacovalent nitrogen. Again wave mechanics does not offer any objections but is in full accord with these classical structures. While a decision between different sets of formulae and concepts cannot be reached by means of any of these additive molecular constants, spectroscopical evidence is leading farther and appears to favor the older classical system and its underlying concepts.