MOS - Molecular Orbitals in Chemical Bonding Chapter 9 Valence Bond Theory Explains the structures of covalently bonded molecules `how bonding

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Molecular Orbitals in Chemical Bonding Chapter 9
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Valence Bond Theory Explains the structures of covalently bonded molecules ‘how’ bonding occurs VSEPR is part of VB theory Principles of VB Theory Bonds form from overlapping atomic orbitals and electron pairs are shared between two atoms A new set of hybridized orbitals can form Lone pairs of electrons are localized on one atom
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Molecular Orbital(MO) Theory Explains the distributions and energy of electrons in molecules Useful for describing properties of compounds Bond energies, electron cloud distribution, and magnetic properties Basic principles of MO Theory Atomic orbitals combine to form molecular orbitals Molecular orbitals have different energies depending on type of overlap Bonding orbitals (lower energy than corresponding AO) Nonbonding orbitals (same energy as corresponding AO) Antibonding orbitals (higher energy than corresponding AO)
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Formation of Molecular Orbitals Recall than an electron in an atomic orbital can be described as a wave function utilizing the Schröndinger equation. The ‘waves’ have positive and negative phases. To form molecular orbitals, the wave functions of the atomic orbitals combine. How the phases or signs combine determine the energy and type of molecular orbital. Look at Figure 9-1 to see how the phases combine.
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Formation of Molecular Orbitals Bonding orbital – the wavefuntions are in- phase and overlap constructively (they add). Bonding orbitals are lower in energy than AOs Antibonding orbital – the wavefunctions are out-of-phase and overlap destructively (they subtract) Antibonding orbitals are higher in energy than the AO’s When two atomic orbitals combine, one bonding and one antibonding MO is formed.
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Overlap of Two 1s Atomic Orbitals Two MO’s are formed when the two 1s atomic orbitals overlap – The in-phase combination produces a σ 1s molecular bonding orbital. Has lower energy than corresponding AO’s
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This note was uploaded on 05/30/2008 for the course CHEM 2070 taught by Professor Chirik,p during the Fall '05 term at Cornell University (Engineering School).

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MOS - Molecular Orbitals in Chemical Bonding Chapter 9 Valence Bond Theory Explains the structures of covalently bonded molecules `how bonding

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