MO Theory MO Theory 1.1 Molecular Orbital Theory 1.2 Failure of Hybrid Orbital Theory Failures of valence bond/hybrid orbital theory – H2S and O2 H H-S-H = 90o MO Theory 1.3 Failure of Hybrid Orbital Theory S H MO Theory 1.4 Molecular Orbital Theory The basic idea Pure s and p atomic orbitals (AOs) combine to produce molecular orbitals (MOs) that “spread spread out out” over several atoms or even the entire molecule Start with atoms at known bond distances Allow AOs with the correct energy, energy size size, shape and orientation to overlap to create MOs 1 MO Theory MO Theory 1.5 Molecular Orbital Theory Basic principles of MO theory Total number of molecular orbitals = total number of atomic orbitals contributed by the atoms AOs combine to form bonding and antibonding MOs Bonding MOs are lower energy than the parent AOs Antibonding MOs are higher energy than the parent AOs Electrons El t are assigned i d tto th the MOs MO ffollowing ll i aufbau fb principle, Hund’s rule and Pauli exclusion principle AOs combine most effectively to form MOs when the AOs are of similar energy (size) and orientation MO Theory 2.1 Dihydrogen Combine the 1s AOs Bond order = MO Theory 2.2 Helium Why is it He instead of He2? 2.3 Other Molecules Li2 Bond order of He2 = 2 MO Theory MO Theory 2.4 Other Molecules and Ions 2.5 Other Ions Be2 He2+ Li2+ Be2+ MO Theory MO Theory 3.1 Shapes of MOs -bonding 3.2 MOs from p-orbitals -bonding 3 MO Theory MO Theory 3.3 MOs from p-orbitals 3.4 Shapes and Energies of the MOs -bonding MO Theory MO Theory 3.5 MO Diagram 3.6 MO Diagrams for N2, O2, F2 4 MO Theory MO Theory 3.7 Simple Diatomics 4.1 Other Molecules and Ions O MO Theory 4.2 Other Molecules and Ions 5
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