The
two theories differ in their predictions about the pairing of electrons.
In the Lewis models, all electrons are paired, whereas with MO theory
B and 0
each have two unpaired electrons in p orbitals
of the same energy. Magnetic measurements of these molecules show
that this is correct: B
and 0 do have
unpaired electrons. This experimental finding is consistent with
MO theory, but cannot be explained by the simple Lewis models. In
this respect, as in others involving quantitative calculations of
energies, MO theory is a vast improvement over simpler electronpair
bond ideas.

