12. Heat, Energy, and Chemical        Bonds   Previous PageNext Page
       Bond Energies

The heats of atomization of elements are heats of dissociation of diatomic gas molecules such as H2, N2, O2, or F2, or of vaporization of solids such as graphite and sulfur into atoms. Since the standard state of sulfur is a solid made up of packed S8 rings, atomization would entail first breaking van der Waals forces and evaporating the S8 molecules, then taking them apart into isolated sulfur atoms.

Notice how the heats of atomization agree roughly with the number of bonds formed by each atom: four bonds in graphite, a triple NN bond in N2, a double bond in O=O, and a single bond in F-F. The single bond in H-H is almost as strong as the double bond in O=O because the H atoms are small and can get close to one another.

The C=C double bond is not quite twice as strong as a single bond because the second shared electron pair does not have as favorable geometry for bonding as does the first pair.

For the same reason, a triple bond is not three times as strong as a single bond. Carbon binds to hydrogen more strongly than to another carbon because of hydrogen's small size and the closer approach of atomic centers.

Sulphur S8 ring

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