On the Theory of the Structure of CH4 and Related Molecules: Part III

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Abstract
(1) Use of Johnson's formulas for sp3 levels in conjunction with existing experimental data makes it doubtful whether the 5S state of the carbon atom is only 1.6 volts above the ground state, as often assumed in the literature. (2) A formula is derived for the energy of the ``valence state'' of the C atom, which is a linear combination of sp3 levels wherein the spins are paired with those of attached atoms. This state is characteristic of tetravalent carbon compounds involving four electron pair bonds, and is shown to involve an increase of about 7 volts in the internal energy of the C atom over that in the ground state. (3) Because of this increment, the net or observed bonding energy is less than the gross or true inter-atomic bonding energy. The gross energy per bond is probably greater in CH3 than in CH4 although the reverse is true of the net. (4) A critical comparison is given of the Slater-Pauling theory of directed valence and the nondirectional Heitler-Rumer |theory based on a 5S state of the C atom. The former leads to much firmer bonds. (5) The assumption of electron pairing, made in Part II, is shown to be well warranted in CH4, as it yields an energy value which is very nearly the same as the deepest root of Eyring and colleague's more exact cubic secular equation. (6) The energies of CH4 and 4CH are compared in the light of theory.