Atomic number of H = 1
Valence electron configuration = 1s¹
When 2 H atoms combine, two 1s orbitals overlap resulting in the formation of a sigma bond.
H₂ Molecular configuration = σ1s²
In H₂⁻ there is an addition of 1 electron which goes to occupy the σ* antibonding orbital:
H₂⁻ = σ1s² σ*1s¹
Thus, 3 electrons will occupy the MO of H2⁻ in which:
2 electrons are bonding
1 electron antibonding
