A simple molecular orbital treatment is presented to explain the bonding in trihalide ions, X3-, XY2-, and XYZ-, and bifluoride ion, HF2-. The M.O.'s are formed from linear combinations of npσ halogen orbitals, and the 1s hydrogen orbital and stable bonding M.O.'s are obtained without the introduction of higher atomic orbitals. Applications are suggested in prediction of other stable species and low energy reaction intermediates.