Chap 9C - Chem 210 WANG Chapter 9C MO Theory Fall 2009...

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Unformatted text preview: Chem 210/ WANG / Chapter 9C MO Theory Fall 2009 UM-SJTU JI 1 Chapter 9.7 Chapter 9.7-9.8 9.8 Bonding Theories: Molecular Orbital Bonding Theories: Molecular Orbital Theory Theory Another model for bonding… View chemical bonds from another perspective ….. Comparison of Bonding Theories Valence Bond Theory (VBT) Electrons still belong to individual atoms individual atoms They are in atomic atomic orbitals (AO) orbitals (AO) that overlap overlap . s Explains: s molecular shape, bond angles, polarity, delocalization of pi electrons s Can not explain Can not explain : s energy levels energy levels of electrons in molecules: Which overlap has higher energy? s " excited states excited states ” of a molecule s paramagnetism paramagnetism versus diamagnetism diamagnetism Comparison of Bonding Theories Molecular Orbital (MO) Theory Electrons belong to the entire molecule entire molecule : They are in molecular orbitals molecular orbitals (MO) S Can explain: Can explain: S Electron energy levels Electron energy levels in a molecule: one MO has higher energy than another. S “ excited states excited states ” of a molecule S paramagnetism paramagnetism versus diamagnetism diamagnetism S Predicts: Predicts: S bond order (number of bonds) bond order (number of bonds) S Why certain atoms will not stay together as a molecule Molecular Orbital (MO) Theory What’s a MO? Similar to Atomic Orbitals (AO)… Molecular Orbitals Molecular Orbitals (MO) are: 1. 1. Wave functions ( Wave functions ( Ψ ) S Ψ 2 = electron density • region in space where electrons are most likely found • Different ‘shapes’: • MO: σ (sigma) and π (pi) • AO: s, p, d, f, etc. S Have nodes nodes = no electron density Molecular Orbital (MO) Theory What’s a MO? Similar to Atomic Orbitals (AO)… Molecular Orbitals Molecular Orbitals (MO) are: 2. 2. Quantized energy levels Quantized energy levels S Energy depends on nuclear attraction • stronger nuclear attraction • closer to a nucleus • lower energy S Some energy levels are degenerated degenerated • different orbitals in the same energy level Molecular Orbital (MO) Theory What’s a MO? Similar to Atomic Orbitals (AO)… 2 ( 2 (conti conti.) .) Quantized energy levels Quantized energy levels S Number of MO equals equals Number of AO used to “make” them • two 1s AO’s merge, resulting in two MO’s: σ 1s and σ 1s * Figure 9.34 Molecular Orbital (MO) Theory What’s a MO? Similar to Atomic Orbitals (AO)… 2 ( 2 (conti conti.) .) Quantized energy levels Quantized energy levels s Order of filling • Electron configuration • Lowest energy level fills first • 2 e capacity per orbital S Hund’s rule s Applies to filling degenerate orbitals s One electron in each orbital before pairing up Molecular Orbital (MO) Theory What’s a MO?...
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Chap 9C - Chem 210 WANG Chapter 9C MO Theory Fall 2009...

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