(1) Use of Johnson's formulas for *sp*^{3} levels in conjunction with existing experimental data makes it doubtful whether the ^{5}*S* 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 *sp*^{3} 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 CH_{3} than in CH_{4} 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 ^{5}*S* 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 CH_{4}, 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 CH_{4} and 4CH are compared in the light of theory.

## REFERENCES

*Phys. Rev.*We have used this model to determine the additive constant in the energy, which was not specified in Johnson’s paper since he took $D3$ as the origin.

*viz.*, the left‐ and right‐handed varieties, or orthogonal linear combinations thereof.

*W*appears only down the principal diagonal and which hence facilitates the application of perturbation theory. In reference 16, a less convenient, non‐orthogonal form is given. The writer is indebted to the various authors mentioned in notes 16 and 17 for the opportunity of seeing their manuscripts in advance of publication.

*k*term see note 13 of the latter reference.

*F*’s and

*G*’s, the gross energies per bond are nearly equal in $CH3$ and $CH4.$ In this case $WV(C)\u223c4\u2009volts,$ Eq. (20) demands $N\sigma s\u2009=\u20090.4$ rather than 1 volt.