How many ion H2- does have
The H2- ion having three electrons. This can be conceived as the combination of a hydrogen atom with a hydride ion (H-). By the aufbau principle, two occupy the bonding molecular orbital, and one occupies the antibonding molecular orbital. Because the bonding molecular orbital haves a greater number of electrons than the antibonding molecular orbital, this species is stable. Notice that in terms of electron occupancy, H2- and He2+ are identical.