Linear Combination of Atomic Orbitals: ψ± = (φ_A ± φ_B)/√(2±2S). The bonding MO (ψ+) has enhanced density between nuclei; the antibonding MO (ψ−) has a nodal plane. H₂⁺ has one electron in the bonding orbital — it is stable.
ψ± = (φ_A ± φ_B) / √(2 ± 2S) | S = ∫φ_A φ_B dV (overlap integral)