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 ( )
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
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. Bonding in BF3 rearrange electrons hydridize orbs. unused p orbital
three sp2
hybrid orbitals 2p 2s
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
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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 Bonding in C2H4
Dr. S. M. Condren

24. s and π Bonding in C2H4
Dr. S. M. Condren

25. s and π Bonding in CH2O
Dr. S. M. Condren

26. s and π Bonding in C2H2
Dr. S. M. Condren

27. s and π Bonding in C2H2
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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 - AB 2 - 0
B => bonding electrons
B - AB
B.O. = = = 1
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 B - AB 2 - 2
Zero bond order means it does not exist
B - AB
B.O. = = = 0
Dr. S. M. Condren

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

33. AO B MO B2 AO B 2p 2p 2s 2s 1s
nonbonding 1s
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 MO C2 AO C 2p 2p 2s 2s 1s
nonbonding 1s
Dr. S. M. Condren

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

37. Energy
Dr. S. M. Condren