Advanced Theories of Chemical Bonding

1. Advanced Theories of Chemical Bonding Atomic Orbitals Molecules

2. Warm-up • What are Lewis Dot Structures for • SO2, SOCl2, SO2Cl2, FSO31- • Draw the Lewis Dot structure for CH4 (methane) • How many bonds does Carbon make? • Write the orbital notation for Carbon (the one with arrows) • There is a conflict in these two models, what is it?

3. Objectives • Understand Hybrid Orbitals • Explain what a hybrid orbital is • Identify hybrid orbitals present within a molecule • Know what a sigma bond is • Know what a pi bond is • Know the consequences of the presence of a pi bond within a molecule

4. 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.

5. Two Theories of Bonding • VALENCE BOND THEORY — Linus Pauling (1901 -1994) • valence electrons are localized between atoms (or are lone pairs). • half-filled atomic orbitals overlap to form bonds.

6. Sigma Bond Formation by Orbital Overlap Two s orbitals overlap

7. Sigma Bond Formation Two s orbitals overlap Two p orbitals overlap

8. Using VB Theory Bonding in BF3 planar triangle angle = 120o

9. 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.

10. 2p 2s hydridize orbs. rearrange electrons 2 unused p three sp orbital hybrid orbitals Notice that from an s and a p subshell, there are four possible equal sp orbitals that COULD be formed Bonding in BF3

11. 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.

12. Bonding in BF3 An orbital from each F overlaps one of the sp2 hybrids to form a B-F  bond.

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.

14. Bonding in a Tetrahedron — Formation of Hybrid Atomic Orbitals 4 C atom orbitals hybridize to form four equivalent sp3 hybrid atomic orbitals.

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

16. Bonding in CH4

17. The end game e- pair geom. Hybrid. Unhybrid. Orbitals Linear sp 2 p’s Trigonal planar sp2 1 p Tetrahedral sp3 0 p Trigonal-bipyramidal sp3d – Octahedral sp3d2 –

19. Bonding in Glycine

20. Bonding in Glycine

21. Bonding in Glycine

22. Bonding in Glycine

23. Bonding in Glycine

24. Bond Types • Sigma (σ) – arise from the overlap of atomic orbitals (including hybridized orbitals) where e- lie along the axis between the nuclei of atoms in bond • Pi (π ) – arise when overlap occurs above or below the nuclei axis (these are p-orbitals that are not hybridized) • FYI D.B. is result of a sigma and a pi • Make C2H2 and CO2, What explains this shape?

25. Multiple Bonds Consider ethylene, C2H4

26. Sigma Bonds in C2H4

27. 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.

28. 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.

29. Multiple Bondingin C2H4

30. sand π Bonding inC2H4

31. sand π Bonding inCH2O

32. sand π Bonding inC2H2

33. Consequences of Multiple Bonding There is restricted rotation around C=C bond.

34. Consequences of Multiple Bonding Restricted rotation around C=C bond.

35. Double Bonds and Vision