heats of atomization of elements are heats of dissociation of diatomic
gas molecules such as H2,
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 NºN
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