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Chapter 10

Chapter 10. Bonding and Molecular Structure: Orbital Hybridization and Molecular Orbitals. Advanced Theories of Chemical Bonding. Atomic Orbitals. Molecules. Two Theories of Bonding. MOLECULAR ORBITAL THEORY — Robert Mullikan (1896-1986) valence electrons are delocalized

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Chapter 10

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  1. Chapter 10 Bonding and Molecular Structure:Orbital Hybridization and Molecular Orbitals Dr. S. M. Condren

  2. Advanced Theories of Chemical Bonding Atomic Orbitals Molecules Dr. S. M. Condren

  3. Two Theories of Bonding • MOLECULAR ORBITAL THEORY — • Robert Mullikan (1896-1986) • valence electrons are delocalized • valence electrons are in orbitals (called molecular orbitals) spread over entire molecule. Dr. S. M. Condren

  4. Two Theories of Bonding • VALENCE BOND THEORY — Linus Pauling • valence electrons are localized between atoms (or are lone pairs). • half-filled atomic orbitals overlap to form bonds. Dr. S. M. Condren

  5. Sigma Bond Formation by Orbital Overlap Two s orbitals overlap Dr. S. M. Condren

  6. Sigma Bond Formation Two s orbitals overlap One s and one p orbital overlap Two p orbitals overlap Dr. S. M. Condren

  7. Using VB Theory Bonding in BF3 planar triangle angle = 120o Dr. S. M. Condren

  8. Bonding in BF3 • How to account for 3 bonds 120o apart using a spherical s orbital and p orbitals that are 90o apart? • Pauling said to modify VB approach with ORBITAL HYBRIDIZATION • — mix available orbitals to form a new set of orbitals — HYBRID ORBITALS — that will give the maximum overlap, in the correct geometry. Dr. S. M. Condren

  9. 2p 2s hydridize orbs. rearrange electrons unused p three sp2 orbital hybrid orbitals Bonding in BF3 Dr. S. M. Condren

  10. Bonding in BF3 • The three hybrid orbitals are made from 1 s orbital and 2 p orbitals  3 sp2 hybrids. • Now we have 3, half-filled HYBRID orbitals that can be used to form B-F sigma bonds. Dr. S. M. Condren

  11. Bonding in BF3 An orbital from each F overlaps one of the sp2 hybrids to form a B-F  bond. Dr. S. M. Condren

  12. BF3, Planar Trigonal Dr. S. M. Condren

  13. Bonding in CH4 How do we account for 4 C—H sigma bonds 109o apart? Need to use 4 atomic orbitals — s, px, py, and pz — to form 4 new hybrid orbitals pointing in the correct direction. Dr. S. M. Condren

  14. Bonding in CH4 Dr. S. M. Condren

  15. Bonding in a Tetrahedron — Formation of Hybrid Atomic Orbitals 4 C atomic orbitals hybridize to form four equivalent sp3 hybrid atomic orbitals. Dr. S. M. Condren

  16. Dr. S. M. Condren

  17. Bonding in Glycine Dr. S. M. Condren

  18. Orbital Hybridization BONDS SHAPE HYBRID REMAIN 2 linear sp 2 p’s 3 trigonal sp2 1 p planar 4 tetrahedral sp3 none Dr. S. M. Condren

  19. Multiple Bonds Consider ethylene, C2H4 Dr. S. M. Condren

  20. Sigma Bonds in C2H4 Dr. S. M. Condren

  21. π Bonding in C2H4 The unused p orbital on each C atom contains an electron and this p orbital overlaps the p orbital on the neighboring atom to form the π bond. Dr. S. M. Condren

  22. π Bonding in C2H4 The unused p orbital on each C atom contains an electron and this p orbital overlaps the p orbital on the neighboring atom to form the π bond. Dr. S. M. Condren

  23. Multiple Bondingin C2H4 Dr. S. M. Condren

  24. sandπBonding in C2H4 Dr. S. M. Condren

  25. sandπBonding in CH2O Dr. S. M. Condren

  26. sandπBonding in C2H2 Dr. S. M. Condren

  27. sandπBonding in C2H2 Dr. S. M. Condren

  28. Consequences of Multiple Bonding There is restricted rotation around C=C bond. Dr. S. M. Condren

  29. Consequences of Multiple Bonding Restricted rotation around C=C bond. Dr. S. M. Condren

  30. Diatomic Molecules AO MO AO H H2 H 1s 1s ENERGY B => bonding electrons B - AB 2 - 0 B.O. = ------------ = -------- = 1 2 2 AB => antibonding electrons all electrons are paired, thus diamagnetic Dr. S. M. Condren

  31. Diatomic Molecules AO MO AO He He2 He 1s 1s ENERGY Zero bond order means it does not exist B - AB 2 - 2 B.O. = ------------ = -------- = 0 2 2 Dr. S. M. Condren

  32. Diatomic Molecules + AO MO AO He He2 He+ 1s 1s ENERGY B - AB 2 - 1 B.O. = ------------ = -------- = 1/2 2 2 One unpaired electron, thus, paramagnetic Dr. S. M. Condren

  33. AO B AO B MO B2 2p 2p 2s 2s 1s 1s nonbonding Dr. S. M. Condren

  34. Molecular Orbital Diagram antibonding MO end-to-end bonding MO antibonding MO side-by-side bonding MO Dr. S. M. Condren

  35. AO C AO C MO C2 2p 2p 2s 2s 1s 1s nonbonding Dr. S. M. Condren

  36. AO O AO O MO O2 2p 2p 2s 2s 1s 1s nonbonding Dr. S. M. Condren

  37. Energy Dr. S. M. Condren

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