1. AP Notes Chapter 9 Hybridization and the Localized Electron Model
Valence Bond Theory
Molecular Orbital Theory
Metals & Semiconductors

2. Hybridization and the Localized Electron
Model
Localized Electron Model developed from
Valence Bond Theory

3. Why do we need it? Consider the water species. H 1s1 O 1s2 2s2 2p4
Gives 2 H’s with no e- and O with full octet.
1s ___
1s ___
2s ___ 2p ___ ___ ___

4. We Get
H 1s1
O 1s2 2s2 2p4
Gives 2 H’s with no e- and O with full octet.
1s ___
1s ___
2s ___ 2p ___ ___ ___

6. Hybridization
Process that changes properties of valence electrons by mixing atomic orbitals to form special orbitals for bonding
atomic molecular orbitals orbitals AO MO

7. Principles 1. Conservation of orbitals
2. Hybrid correlates with molecular geometry
3. Energy level of MO is between that of AO’s
4. All bonded atoms hybridize

8. WHEN ATOMS BOND
atomic
orbital
hybrid
orbital

9. All hybrid orbitals of an atom are said to be DEGENERATE
(of equal energy)

10. CH4 C: AO 2p __ __ __ s ____ H C H H H

11. CH MO __ __ __ __ H C H H H
sp3 hybrid orbitals

12. 4 Items Equally Distributed
sp3 hybridization
sp3 hybrid orbitals
tetrahedral species
sp3 shape tetragonal
4 Items Equally Distributed

13. Tetragonal

14. C C H H H H H H H H Lewis Structure Electron Pair Geometry
Molecular Model C H H H H C H H H

15. InCl3 In: AO 5p __ __ __ 5s _____

16. InCl MO
__ __ __ Cl In
5p __ Cl Cl
sp2 hybrid orbitals

17. trigonal planar species 3 Items Equally Distributed
sp2 hybridization
sp2 hybrid
trigonal planar species
sp2 shape
3 Items Equally Distributed

18. BaCl2 Cl - Ba - Cl Ba: AO
6p ___ ___ ___ s _____

19. BaCl2 Cl - Ba - Cl Ba: MO 6p ___ ___
sp hybrid orbitals

20. 2 Items Equally Distributed
sp hybridization
sp hybrid
linear species
sp shape
2 Items Equally Distributed

21. PF5 P: AO 3d ___ ___ ___ ___ ___ 3p ___ ___ ___ 3s ____

22. PF5 P: MO 3d ___ ___ ___ ___
___ ___ ___ ___ ___
sp3d hybrid orbitals

23. 5 Items Equally Distributed
sp3d hybridization
sp3d shape
trigonal bipyramid
species
5 Items Equally Distributed

24. SF6 S: AO 3d ___ ___ ___ ___ ___ 3p _____ ___ ___ 3s _____

25. SF6 S: MO 3d ___ ___ ___ ___ ___ ___ ___ ___ ___
sp3d2 hybrid orbitals

26. 6 Items Equally Distributed
sp3d2 hybridization
sp3d2 shape
octahedral species
6 Items Equally Distributed

27. Multiple Bonds
sigma bonds ()
pi bonds ()

28. EXAMPLES O2 2 p-orbitals touching end to end sigma - σ
O 1s2 2s2 2p p4 2s2 1s2 O
2 p-orbitals touching end to end sigma - σ
2p-electrons reaching over and under pi - π
2s ___ 2p ___ ___ ___
2p ___ ___ ___ 2s ___
___ ___

29. Valence Bond Theory Multiple Bond Examples
C2H4 (ethylene)
s (sp3 hybridization)
p ( bonding)
both

31. EXAMPLES
C2H2

33. EXAMPLES
CH3COOH

34. MOLECULAR ORBITAL MODEL
Valence Bond Theory concentrates on individual bonds in a molecule and tends to ignore electrons not used in bonding.

35. Molecular Orbital Theory assumes ALL the orbitals of the atoms are able to take part in bonding.

36. Every atom has a complete set of orbitals, but not all of them contain electrons

37. Remember that orbitals are really the solutions of Schrodinger’s equation, and that they are called
wave-functions

38. 1s wavefunction r

39. - +
Negative
here
Positive
2pz wavefunction

40. 2pz orbital - +
1s orbital

41. While wave functions can be positive or negative, probabilities can only be positive.

42. Wave functions, like waves, can overlap with one another
Wave functions, like waves, can overlap with one another. They can reinforce each other, or they can cancel each other out.

43. . +
plus
1sA
1sB B A
A sigma, s, bonding orbital

44. . + -
minus
1sA
1sB B A
A sigma star, s*,
anti-bonding orbital

45. The work on molecular orbitals can be generalized to
p-orbitals.

46. 2pz
s2p
A s2p bonding orbital

47. 2pz
s2p*
A s2p*
antibonding orbital

48. plus A B
2py
p2p
A p2p bonding orbital

49. minus A B
2py
p2p*
A p2p*
antibonding orbital

50. Many combinations of orbitals can produce bonding and anti-bonding molecular orbitals, s with p,
d with p, etc.

51. Orbitals on the two bonding atoms must meet 2 conditions
They must be similar in energy
They must have the right symmetry

52. plus
2pz
2pz
2py
2py
Orbitals pointing in different directions cannot overlap to form molecular orbitals.

53. Molecular Orbital Theory
1. Molecular orbitals are made from atomic orbitals
2. Orbitals are conserved
3. Molecular orbitals form in pairs: bonding & antibonding

54. Bonding Molecular Orbital
Geometry favorable to overlap

55. When a bonding orbital is formed, the energy of the orbital is lower than those of its parent atomic orbitals.

56. Anti-bonding Molecular Orbital
Geometry not favorable to overlap

57. Similarly, when an anti-bonding orbital is formed, the energy of the orbital is higher than those of its parent atomic orbitals.

58. Molecular Orbital Diagrams
Bond Order

59. Examine some homonuclear diatomic molecules
Hydrogen
Helium

60. s2s*
1sA
1sB
s2s

61. Paramagnetic
1. Responds to magnetic field
2. Has unpaired electrons

62. Diamagnetic 1. Does not respond to magnetic field
2. All electron paired

63. 1s 2s
2px
2py
2pz
s1s
s1s*
s2s
s2s*
s2p
p2p
s2p*
p2p*
fluorine gas

64. 1s 2s
2px
2py
2pz
s1s
s1s*
s2s
s2s*
s2p
p2p
s2p*
p2p*
oxygen gas

65. Using MO Theory, molecules have an electron configuration
Oxygen gas
(s1s)2(s1s*)2
(s2s)2(s2s*)2
(p2py)2 (p2py*)2
(s2pz)2 (p2px)2

66. nitrogen gas 1s 2s 2px 2py 2pz s1s s1s* s2s s2s* s2p p2p s2p* p2p*
Magnet Movie

67. Bond Strength
Bond Length

68. Strengths of Localized Electron Model
1. Simple
2. Easy to understand
3. Predicts geometry of molecule

69. Limitations of Localized Electron Model
1. Does not address concept of resonance or unpaired e-
2. Cannot explain color in transition metal compounds

70. Strengths of Molecular Orbital Model
1. Better represents actual molecular system
2. Provides basis for explaining properties of molecular systems

71. Limitations of Molecular Orbital Model
1. MO diagrams are complex.
2. MO diagrams are difficult for molecules with more than two atoms.
3. No prediction of geometry

72. Combining the Localized Electron
and
Molecular Orbital
Models

73. Draw the Lewis structure of benzene
C6H6
Lewis Structure

74. C2H4 + Br2  C2H4Br2
C6H6 + Br2  NR

75. s bonds in benzene
p bonds in benzene
benzene

76. Isomerism
Isomers – two or more compounds with same molecular formula but different arrangements of atoms
Cis – Trans Isomerism (NOT mirror images of each other NOT super imposable.
Cis Trans

77. Resonance and MO X X
The more resonance structures the more stable the molecule

78. Metals & Semiconductors
Read pg
Study Figures 1-23
Know
Insulators
Conductors, Semiconductors – intrinsic, extrinsic
Dopants