It is proposed that the valence number, n,
for bonding in the elemental state may be estimated by n = rΔHf�/C,
where r is half the interatomic distance, -ΔHf� is the heat of formation of the elemental state,
and C is a constant and approximately 28 and 40 Ǻ kcal g-atom-1
for non-metals and metals respectively.
It is shown that the valence states of the
elementary transition metals, as given by n, correspond closely to the most
stable oxidation states (MSOS) displayed in binary transition metal fluorides,
chlorides, and related compounds.
It is concluded that the trend of the MSOS
of transition metal binary compounds results mainly from each metal possessing
a preferred valence state, which is strongly determined by the availability of
the (n-l)d orbitals for bonding as judged by their size relative to that of the
ns and p orbitals.
Elementary transition systems
