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 electron-pair bond ideas.