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Two Bonding Theories

Two Bonding Theories. Valence Bond Theory (localized electron model) Electrons in a molecule still occupy orbitals of individual atoms . Molecular Orbital Theory Says that atomic orbitals no longer exist. Molecular orbitals are available for occupation by electrons .

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Two Bonding Theories

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  1. Two Bonding Theories • Valence Bond Theory (localized electron model) • Electrons in a molecule still occupy orbitals of individual atoms. • Molecular Orbital Theory • Says that atomic orbitals no longer exist. Molecularorbitals are available for occupation by electrons.

  2. Valence Bond Theory • Electrons in a molecule still occupy orbitals of individual ATOMS. • Half-filled orbitals of two atoms overlap.

  3. VB Theory: Formation of H2S

  4. VB Theory: Formation of H2S

  5. 2s 2p VB Theory: Carbon Would suggest only two bonds possible

  6. 2s 2p VB Theory: Carbon What if we just bump an electron up? Would suggest two different types of bonds form (one with an s orbital and three with p orbitals)

  7. Valence Bond Theory • Atomic Orbitals Hybridize. • These are still atomic orbitals. • Two or more nonequivalent orbitals of sameatom combine. • When X number of atomic orbitals hybridize, X number of hybrid orbitals will result.

  8. 2s 2p 2sp3 VB Theory: Carbon Four atomic orbitals (one s and three p) hybridize into four degenerate hybrid orbitals, as a group called sp3

  9. How will four degenerate orbitals exist around the central atom?

  10. How will four degenerate orbitals exist around the central atom?

  11. VB Theory: NH3

  12. VB Theory: sp3 hybridization

  13. VB Theory: sp2 hybridization

  14. VB Theory: sp2 hybridization

  15. VB Theory: sp2 hybridization

  16. C2H4, sp2 hybridization

  17. Valence Bond Theory Hybridization is directly connected to the Electron-pair Geometry sp3 sp2 sp = linear sp3d = trig bipryramidal sp3d2 = octahedral • = tetrahedral = trigonal planar

  18. Molecular Orbital Theory • Says that atomic orbitals no longer exist. • Molecular orbitals are available for occupation by electrons. • Atomic orbitals from all atoms overlap and become an equivalent number of molecular orbitals.

  19. Molecular Orbital Theory Constructive vs. Destructive Interference

  20. Molecular Orbital Theory

  21. Molecular Orbital Energy Diagramfor H2

  22. Molecular Orbital Energy Diagramfor He2

  23. Molecular Orbital Theory

  24. Molecular Orbital Theory

  25. Molecular Orbital Theory

  26. Molecular Orbital Theory • Sigma Bond – electron density along line joining two nuclei - from the side, would look like an s orbital - first bond that forms between two nuclei (single bond) bonding: s1s • antibonding: s*1s • s2p • s*2p

  27. Molecular Orbital Theory • Pi Bond– formed by sideways overlapping of orbitals, electron density above and below plane of nuclei – second / third bond that forms between two nuclei (double / triple bonds) - less overlap means weaker than sigma bonds

  28. from Susan Piepho, Sweet Briar College

  29. http://lhs2.lps.org/staff/squiring/chemistry/Chap15_16.2/CarbonHybridization.htmlhttp://lhs2.lps.org/staff/squiring/chemistry/Chap15_16.2/CarbonHybridization.html

  30. http://lhs2.lps.org/staff/squiring/chemistry/Chap15_16.2/CarbonHybridization.htmlhttp://lhs2.lps.org/staff/squiring/chemistry/Chap15_16.2/CarbonHybridization.html

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