1. Molecular Geometry and Bonding Theories

2. Two Simple Theories of Covalent Bonding
Valence Shell Electron Pair Repulsion Theory
VSEPR
R. J. Gillespie ’s
Valence Bond Theory
Hybridized orbitals
L. Pauling ’s & 40’s 2 2

3. Stereochemistry Study of the 3 dimensional shapes of molecules
TWO MODELS
VSEPR Theory
Valence Bond Theory
Some questions to examine:
Why are we interested in shapes?
What role does molecular shape play in life?
How do we determine molecular shapes?
How do we predict molecular shapes? 3 3

4. Determining Molecular Structure
Draw the Lewis dot structure
identify central atom
Count # of regions of high electron density on central atom
VSEPR tells the geometry around central atom 4 4

5. Determining Molecular Structure
Identify lone pair effect on ideal molecular geometry
Repeat procedure for more than one central atom
Determine polarity from entire molecular geometry
electronegativity differences 5 5

6. VSEPR Theory
regions of high electron density around the central atom go as far apart as possible to minimize repulsions
five basic shapes
based on # of regions of high electron density
several modifications of these five basic shapes will also be examined 6 6

7. VSEPR Theory
Two regions of high electron density 7 7

8. VSEPR Theory
Three regions of high electron density 8 8

9. VSEPR Theory
Four regions of high electron density 9 9

10. VSEPR Theory
Five regions of high electron density 10 10

11. VSEPR Theory
Six regions of high electron density 11 11

12. VSEPR Theory electronic geometry (electron domain) molecular geometry
determined by the locations of regions of high electron density around the central atom(s)
molecular geometry
determined by the arrangement of atoms around the central atom(s)
electron pairs are not used in the molecular geometry determination 12 12

13. VSEPR Theory CH4 - methane electronic geometry molecular geometry
tetrahedral
molecular geometry
bond angles = 109.5o 12 12

14. VSEPR Theory H2O - water electronic geometry molecular geometry
tetrahedral
molecular geometry
bent or angular
bond angle = 13 13

15. VSEPR Theory
lone pairs of electrons (unshared pairs) require more volume than shared pairs
there is an ordering of repulsions of electrons around central atom 14 14

16. VSEPR Theory lone pair to lone pair repulsion is strongest
lone pair to bonding pair repulsion is intermediate
bonding pair to bonding pair repulsion is weakest
mnemonic for repulsion strengths
lp/lp > lp/bp > bp/bp
lone pair to lone pair repulsion is why bond angles in water are less than 14 14

17. Valence Bond Theory
covalent bonds are formed by overlap of atomic orbitals
atomic orbitals on the central atom can mix and exchange their character - hybridization
common hybrids
pink flowers, mules, corn, grass 15 15

18. Valence Bond Theory hybridized orbitals describe same shapes as VSEPR
Name of orbital Shape of orbital
sp3 tetrahedral
sp2 trigonal planar
sp linear
sp3d trigonal bipyramidal
sp3d2 octahedral 15 15

19. Hybrid Orbitals Electronic Structures Lewis Formulas 1s 2s 2p Be ­¯ ­¯
Cl [Ne] ­¯ ­¯ ­¯ ­ 16 16

20. Hybrid Orbitals
Dot Formula Electronic Geometry 17 17

21. Hybrid Orbitals
VSEPR Polarity 17 17

22. Hybrid Orbitals
VSEPR Polarity 17 17

23. Hybrid Orbitals Molecular Geometry same as electronic geometry
symmetrical & nonpolar 18 18

24. Hybrid Orbitals Valence Bond Theory (Hybridization)
1s 2s 2p 1s sp hyb 2p
Be ­¯ ­¯ Þ­¯ ­ ­
3s p
Cl [Ne] ­¯ ­¯ ­¯ ­ 19 19

25. Hybrid Orbitals Linear

26. Hybrid Orbitals examples all are trigonal planar, nonpolar molecules
BF3, BCl3
all are trigonal planar, nonpolar molecules 20 20

27. Hybrid Orbitals Electronic Structures Lewis Formulas 1s 2s 2p
Cl [Ne] ­¯ ­¯ ­¯ ­ 20 20

28. Hybrid Orbitals
Dot Formula Electronic Geometry 21 21

29. Hybrid Orbitals
VSEPR Polarity 21 21

30. Hybrid Orbitals
Molecular Geometry 22 22

31. Hybrid Orbitals Valence Bond Theory (Hybridization)
1s 2s 2p s sp2 hybrid
B ­¯ ­¯ ­ Þ ­¯ ­ ­ ­
5s p
Cl [Ne] ­¯ ­¯ ­¯ ­ 23 23

32. Hybrid Orbitals Trigonal Planar

33. Hybrid Orbitals examples all are tetrahedral, nonpolar molecules
CH4, CF4, CCl4, SiH4, SiF4
all are tetrahedral, nonpolar molecules
as long as they have the same 4 substituents 24 24

34. Hybrid Orbitals 2s 2p C [He] ­¯ ­ ­
Electronic Structures Lewis Formulas
2s p
C [He] ­¯ ­ ­ 24 24

35. Hybrid Orbitals 2s 2p C [He] ­¯ ­ ­ 1s H ­
Electronic Structures Lewis Formulas
2s p
C [He] ­¯ ­ ­ 1s
H ­ 24 24

36. Hybrid Orbitals
Dot Formula Electronic Geometry 25 25

37. Hybrid Orbitals
VSEPR Polarity 25 25

38. Hybrid Orbitals
Molecular Geometry 26 26

39. Hybrid Orbitals Valence Bond 2s 2p four sp3 hybrid orbitals
C [He] ­¯ ­ ­ Þ C [He] ­ ­ ­ ­ 1s
H ­ 27 27

40. Hybrid Orbitals Tetrahedron

41. Hybrid Orbitals Examples
PF5, AsF5, PCl5, etc.
All are trigonal bipyramidal, nonpolar molecules. 41

42. Hybrid Orbitals 4s 4p As [Ar] 3d10 ­¯ ­ ­ ­ 2s 2p F [He] ­¯ ­¯ ­¯ ­
Electronic Structures Lewis Formulas
4s p
As [Ar] 3d10 ­¯ ­ ­ ­
2s p
F [He] ­¯ ­¯ ­¯ ­ 42

43. Hybrid Orbitals
Dot Formula Electronic Geometry 43

44. Hybrid Orbitals
VSEPR Polarity 44

45. Hybrid Orbitals
VSEPR Polarity 44

46. Hybrid Orbitals
Molecular Geometry 45

47. Hybrid Orbitals Valence Bond (Hybridization) 4s 4p 4d
As [Ar] 3d10 ­¯ ­ ­ ­ ___ ___ ___ ___ ___ ß
five sp3 d hybrids
­ ­ ­ ­ ­ 45

48. Hybrid Orbitals Trigonal Bipyramidal Molecules
Valence Bond (Hybridization) 45

49. Hybrid Orbitals Trigonal Bipyramid Molecules
Valence Bond (Hybridization)

50. Variations of Trigonal Bipyramidal Shape
If lone pairs are incorporated into the trigonal bipyramidal structure, there are three possible new shapes.
One lone pair - seesaw shape
Two lone pairs - T-shape
Three lone pairs - linear

51. Hybrid Orbitals Example These are octahedral and nonpolar molecules.
SF6, SeF6, SCl6, etc.
These are octahedral and nonpolar molecules.
if all 6 substituents are the same 46

52. Hybrid Orbitals Se [Ar] 3d10 ­¯ ­¯ ­ ­ 2s 2p F [He] ­¯ ­¯ ­¯ ­
Electronic Structures Lewis Formulas s p
Se [Ar] 3d10 ­¯ ­¯ ­ ­
2s p
F [He] ­¯ ­¯ ­¯ ­ 47

53. Hybrid Orbitals
Dot Formula Electronic Geometry 48

54. Hybrid Orbitals
VSEPR Polarity 49

55. Hybrid Orbitals
VSEPR Polarity 49

56. Hybrid Orbitals
Molecular Geometry 50

57. Hybrid Orbitals Octahedral Molecules
Valence Bond (Hybridization)
4s p d
Se [Ar] 3d10 ­¯ ­¯ ­ ­ __ __ __ __ __ ß
six sp3 d2 hybrids
­ ­ ­ ­ ­ ­

58. Hybrid Orbitals Octahedral Molecules
Valence Bond (Hybridization)

59. AB6- No Lone Pairs - Octahedral Molecules

60. Variations of Octahedral Shape
If lone pairs are incorporated into the octahedral structure, there are two possible new shapes.
One lone pair - square pyramidal
Two lone pairs - square planar

61. Compounds Containing Double Bonds
Ethene or ethylene is the simplest double bond containing organic compound.
Lewis Dot Formula for ethene C2H4
N = 2(8) + 4(2) = 24
A = 2(4) + 4(1) = 12
S = 12 51

62. Compounds Containing Double Bonds
Lewis Dot Formula for ethene C2H4 51

63. Compounds Containing Double Bonds
VSEPR
suggests C atoms at center of two equilateral triangles H H C C H H 52

64. Compounds Containing Double Bonds
Valence Bond Theory
sp2 hybrids for the C atoms
1 electron remains in an unhybridized p orbital
2s 2p three sp2 hybrids 2p
C ­¯ ­ ­ Þ ­ ­ ­ ­ 53

65. Compounds Containing Double Bonds
C atoms are sp2 hybridized with single electrons in each of the lobes
Top view

66. Compounds Containing Double Bonds
The unhybridized 2p orbital on the C atom lies perpendicular to the planar sp2 lobes.
Side view 54

67. Compounds Containing Double Bonds
C=C double bond results from head-on overlap of two sp2 hybrid orbitals 55

68. Compounds Containing Double Bonds
The portion of the double bond formed from the head-on overlap of the sp2 hybrids is designated as a s bond. 56

69. Compounds Containing Double Bonds
The other portion of the double bond, resulting from the side-on overlap of the p orbitals, is designated as a p bond.

70. Compounds Containing Double Bonds
The final result is a bond that looks like this.

71. Compounds Containing Triple Bonds
Ethyne or acetylene is the simplest triple bond containing organic compound.
Lewis Dot Formula for ethyne C2H2
N = 2(8) + 2(2) = 20
A = 2(4) + 2(1) =10
S = 10 51

72. Compounds Containing Triple Bonds
Lewis Dot Formula for ethyne C2H2 51

73. Compounds Containing Triple Bonds
VSEPR
suggests C and H atoms are 180o apart.
H C C H 52

74. Compounds Containing Triple Bonds
Valence Bond Theory
sp hybrids for the C atoms
2 electrons remain in unhybridized p orbitals 53

75. Compounds Containing Triple Bonds
Valence Bond Theory
sp hybrids for the C atoms
2 electrons remain in unhybridized p orbitals
2s 2p two sp hybrids 2p
C ­¯ ­ ­ Þ ­ ­ ­ ­ 53

76. Compounds Containing Triple Bonds
triple bond results from head-on overlap of two sp hybrid orbitals 55

77. Compounds Containing Triple Bonds
Note that this gives us one s bond and two p bonds. 56

78. Compounds Containing Triple Bonds
The final result is a bond that looks like this.

79. Summary of Electronic & Molecular Geometries

80. Synthesis Question 1
The basic shapes that we have discussed are present in essentially all molecules. Shown below is the chemical structure of vitamin B6 phosphate. What is the shape and hybridization of each of the indicated atoms in vitamin B6 phosphate?

81. Synthesis Question 1

82. Group Question 1
Shown below is the structure of penicillin-G. What is the shape and hybridization of each of the indicated atoms in penicillin-G?

83. Synthesis Question 2
As we all know, in the wintertime we are more likely to get shocked when we walk across carpet and touch the door knob. Here is another wintertime experiment to perform. Turn on a water faucet until you have a continuous but small stream of water coming from the faucet. Brush your hair vigorously then hold the brush near the stream of water. You will notice that the stream bends towards the brush. Why does the water bend?

84. Synthesis Question 2
Since water is a highly polar molecule, it is attracted by the electromagnetic field generated by the hair brush. This causes the stream to bend.

85. Group Question 2
On a recent “infomercial” it was claimed that placing a small horseshoe magnet over the fuel intake line to your car’s carburetor would increase fuel mileage by 50%. The reason given for the mileage increase was that “the magnet aligned the molecules causing them to burn more efficiently.” Will this work? Should you buy this product?