03-21-2011 Lecture

03-21-2011 Lecture - Overview Before We Start. . . Last Few...

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Overview Before We Start. . . Last Few Lectures - Valence bond theory (localized electron pairs forming bonds) - Lewis structures number of electron pairs and bond order - VSEPR repulsion of e pairs (BP and LP) molecular shape - Hybridization combining AOs on one atom hybrid orbitals The Next Three Lectures - Molecular orbital theory (delocalized view of bonding) - LCAO – in MOs, all AOs can contribute to a MO, not just valence e- - n AOs n MOs - orbitals filled in same way as AOs - we will see many examples, mostly diatomics (H 2 , N 2 , CO, etc.)
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Motivation for Molecular Orbitals What are weaknesses of the Localized Electron (LE) Model? 1) It’s not good at dealing with resonance structures (since it considers localized electrons) 2) Not very useful when considering odd-numbered electron species (since Lewis Structures typically are drawn for pairs of electrons) 3) Not very good at determining bond strengths or magnetic properties of molecules We will develop a molecular orbital model, which deals with problems #1-3, and even in its simplest form is useful for understanding bonding and properties of homo- and heteronuclear diatomic molecules (H 2 , H 2 + , O 2 , N 2 , NO, etc.) • the drawback of MO theory is that it is more complicated and the molecular orbitals are more difficult to visualize than the easily depicted shapes of VSEPR or the hybrid orbitals in the localized electron model.
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This note was uploaded on 10/13/2011 for the course CHEM 101 taught by Professor Fitts during the Fall '08 term at UPenn.

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03-21-2011 Lecture - Overview Before We Start. . . Last Few...

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