11-3-08%20-%20Lecture%2014%20-%20Chapter%203

11-3-08%20-%20Lecture%2014%20-%20Chapter%203 - Theories of...

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Unformatted text preview: Theories of Chemical Bonding Chemical Atomic Orbitals Molecules Two Theories of Bonding Two • VALENCE BOND THEORY • valence electrons are localized between atoms (or are lone pairs). • half-filled atomic orbitals overlap to form bonds. • hybridization Two Theories of Bonding • MOLECULAR ORBITAL THEORY — • Electrons are delocalized in orbitals (called molecular orbitals) spread over entire molecule. • Electrons do not belong to any one atom Sigma Bond Formation by Orbital Overlap Orbital Two s orbitals Two overlap overlap Sigma Bond Formation for HF Sigma Bonds in N Bonds How do we account for 4 C—H sigma bonds 109o apart? 109o Bonding in CH Bonding Bonding in CH4 Bonding Bonding in a Tetrahedron — Formation of Hybrid Atomic Orbitals of 4 C atom orbitals hybridize to form four equivalent sp3 hybrid atomic orbitals. Bonding in CH4 Bonding • Bonding is due to an overlap of an sp3 orbital from Carbon and a 1s orbital from Hydrogen Hybridization and Molecular Shape Determining Hybridization Determining 1) Draw the correct Lewis Structure 2) Count the number of “things” attached to the central atom (remember lone pairs count as things and multiple bonds count as only one thing) 3) Remember the order of atomic orbitals spppdddd 1) Starting with the s-orbital, count off an orbital for every “thing” that is attached to the central atom 2) The hybridization will be spxdy where x and y are the number of orbitals you used in (4) above. σ and π Bonding in C2H4 and σ and π Bonding in C2H2 and ...
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