lectures25+26 (12-6-2006) Ch 11

lectures25+26 (12-6-2006) Ch 11 - 1 MOLECULAR ORBITAL...

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Unformatted text preview: 1 MOLECULAR ORBITAL THEORY: More correct than valence bond theory to treat chemical bonding Electrons occupy orbitals each of which spans the entire molecule - DELOCALIZED Molecular orbitals each hold up to two electrons and obey Hunds rule, just like atomic orbitals. Basic idea: Electron density between atoms gives a chemical bond Chemistry 2A Chemistry 2A-c F2006 c F2006 (Ch11 (Ch11-40)309 40)309 2 Formation of Molecular Orbitals 1 s A + 1 s B = MO 1 A B r/a- 3/2 1 e 1 2 ) ( = = a r R s A B + Increase electron density in overlap region Bonding MO 1 s Chemistry 2A Chemistry 2A-c F2006 c F2006 (Ch11 (Ch11-41)310 41)310 3 Deplete electron density in overlap region.. 1 s A 1 s B = MO 2 A B Anti-bonding MO 1 s * Chemistry 2A Chemistry 2A-c F2006 c F2006 (Ch11 (Ch11-42)311 42)311 4 E 1 s 1 s * 1 s 1 s H H H 2 The electrons are placed in the 1 s molecular orbitals. The bonding in H 2 Chemistry 2A Chemistry 2A-c F2006 c F2006 (Ch11 (Ch11-43)312 43)312 5 E 1 s 1 s * 1 s 1 s H 2 : ( 1 s ) 2 H H H 2 Two electrons in the 1 s bonding orbital stable molecule Chemistry 2A Chemistry 2A-c F2006 c F2006 (Ch11 (Ch11-44)313 44)313 6 E 1 s 1 s * 1 s 1 s Is He 2 a stable molecule? He He He 2 One pair of electrons goes in 1 s and the next pair in 1 s * (1s 2 ) (1s 2 ) Chemistry 2A Chemistry 2A-c W2006 c W2006 (Ch12 (Ch12-45)314 45)314 7 E 1 s 1 s * 1 s 1 s He 2 : ( 1 s ) 2 ( 1 s *) 2 He He He 2 The bonding effect of ( 1 s ) 2 is cancelled by the antibonding effect of ( 1 s *) 2 He 2 is not a stable molecule....
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This note was uploaded on 04/23/2008 for the course CHEM 2A taught by Professor Guo during the Fall '08 term at UC Davis.

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lectures25+26 (12-6-2006) Ch 11 - 1 MOLECULAR ORBITAL...

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