W2013CHM2311 Part 4a Notes

W2013CHM2311 Part 4a Notes - CHM2311 Introduc0on to...

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CHM2311’ Introduc0on’to’Structure’&’Bonding’ Part’4’ Molecular’Orbital’Theory’
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Models’of’Covalent’Bonding’ Lewis’formalism;’atoms’seek’an’inert’gas’conFgura0on.’ C H H H H Lewis’ V alence’ S hell’ E lectron’ P air’ R epulsion’( VSEPR )’Theory.’Pairs’of’electrons’avoid’one’another’ like’charges’on’a’sphere. H C H H H VSEPR’ V alence’ B ond’( VB )’Theory.’Combina0ons’of’atomic’orbitals’provide’electron’pair’bonds.’ Hybrids’ orient’electron ’pairs . C VB’Theory ’ M olecular’ O rbital’( MO )’Theory.’Energy’levels’within’molecules.’ MO’Theory ’
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Models’of’Covalent’Bonding’ C H H H H Lewis’ H C H H H VSEPR’ V alence’ B ond’( VB )’Theory.’Combina0ons’of’atomic’orbitals’provide’electron’pair’bonds.’ Hybrids’ orient’electron ’pairs . C M olecular’ O rbital’( MO )’Theory.’Energy’levels’within’molecules.’ Quantum’mechanical’models’for’bonding’describe’electrons’as’waves.’ VB’Theory ’ MO’Theory ’
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VB’Theory’and’MO’Theories’ The’Main’Diferences’ In VB theory we hybridize atomic orbitals (add/subtract them) on same atom to direct electron pairs. In MO theory we add/subtract atomic orbitals on diferent atoms create orbitals that span two or more atoms. C MO theory provides us with an Au±au type descrip²on oF energy levels in molecules. Hybrids on diferent atoms are then mul²plied together. Pictorially easy, mathema0cally complex.
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Models’of’Covalent’Bonding’ C H H H H Lewis’ H C H H H VSEPR’ C VB’Theory ’ MO’Theory ’ Localized bonding models: Lewis Theory, Valence Bond Theory Electrons’in’a’bond’ are’considered’to’be’ localized’between’the’two’atoms’that’are’joined’by’the’bond.’ The’electrons’stay’between’those’atoms;’they’can’NOT’change’loca0ons’and’they’ do not move around the molecule .’ Delocalized bonding models: Resonance Theory, Molecular Orbital Theory Electrons’in’a’molecule’are’no’longer’considered’as’belonging’to’a’speciFc’atom.’They’are’not’stuck’ in’ any’ given’ loca0on.’ Rather,’ all’ electrons’ belong’ to’ the’ molecule’ as’ a’ whole,’ and’ can’ move’ throughout’the’molecule.’
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Molecular’Orbital’Bonding’Models’ General ProperBes: Molecular’orbitals’(MO)’are’similar’in’many’ways’to’atomic’orbitals’(AO).’They’are’ the’solu0ons’to’the’wave’equa0on’for’molecules.’ Exact’solu0ons’to’the’wave’equa0ons’for’molecules’are’difficult’to’Fnd’(e.g.’dealing’ with’e - -e - ’interac0ons),’but’several’methods’of’Fnding’approximate’solu0ons’exist.’ Ha Hb e 1 e 2 ra 1 rb 1 rb 2 ra 2 r 12 R The Schrodinger equa?on revisited… + + + + Λ Ν Μ Ξ Π Ο h m e ra rb ra rb r R 8 1 1 1
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W2013CHM2311 Part 4a Notes - CHM2311 Introduc0on to...

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