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## BONDING

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**BONDING**Two main ways of thinking about bonding: 1. Valence Bond Theory -all bonds are localized interactions involving 2 electrons and 2 nuclei -leads to orbital hybridization as a method to manipulate the AOs. -no resonance, no delocalization 2. Molecular Orbital (MO) Theory -assigns electrons to MOs which are delocalized over the entire molecule Which is better? Both are approx. -VB theory fails to explain bonding in aromatic compounds -VB theory fails to predict that O2 is paramagnetic -MO theory more consistent with spectroscopy**BONDING**Why do we need approximate methods at all? 1. exact solutions are not possible even for H2 2. approx. methods can give insight and physical understanding into chemical bonding MO Theory : consists of 3 main approximations 1. Born-Oppenheimer approximation 2. Independent electron (orbital) approximation 3. LCAO approximation