This molecular buildup is tabulated above. The molecule-ion has only one electron, which occupies the bonding orbital by itself. This electron spends most of its time between the nuclei, shielding them from one another and holding them together like half of a Lewis electron-pair bond. Two electrons are present in H and they completely fill the bonding MO. This is the ordinary electron-pair bond discussed in Chapter 4.

has three electrons, and since two of them fill the MO, the third is forced into the antibonding orbital. The molecule has two electrons holding the nuclei together, and one pulling them apart, for a net of one bonding electron. The antibonding electron weakens the molecule. He would have two electrons in the bonding orbital and two in the antibonding orbital. The push and pull of these electrons cancel, and no net bonding is left in the He Molecule, which therefore does not exist.