1. Chapter 9
Molecular Geometry

2. Molecular Shapes
Lewis Structures do not account for shape of molecules rather they only show the number and types of bonds between atoms

3. Molecular Shapes
The overall shape is determined by the bond angle, the angle made by the lines joining the nuclei of the atoms in a molecule

4. Molecular Shapes
We will focus on atoms with ABn format, a central atom A has n B atoms bonded to it

5. VSEPR Model
An electron domain consists of nonbonding pairs, single bonds, or multiple bonds

6. VSEPR Model

7. VSEPR Model
Electron domains are negatively charged, so they repel each other, and stay out of each other’s way

8. VSEPR Model
the best arrangement of a given number of electron domains is the one that minimizes the repulsions among them

9. VSEPR Model
The shape of the substance in the ABn format depends on the number of electron domains surrounding the central atom (Electron-domain geometry)

10. VSEPR Model
Molecular shape describes the arrangement of atoms, not the electron domains (molecular geometry)

11. VSEPR Model
To Predict Shapes:
1. Draw Lewis structure and count e-d
2. Determine e-d geometry
3. Predict molecular geometry

12. VSEPR Model
See table

13. VSEPR Model

14. Basic Geometry 0 lone pairs 1 lone pair 2 lone pairs 3 lone pairs
Domains
Basic Geometry 0 lone pairs
1 lone pair
2 lone pairs
3 lone pairs 2
Linear 3
trigonal planar
bent 4
tetrahedral
trigonal pyramidal 5
trigonal bipyramidal
seesaw
T-shaped
linear 6
octahedral
square pyramidal
square planar 15

15. VSEPR Model

16. Sample Ex
Use VSEPR to predict shape for the following substances: O3
SnCl3-
SeCl2
CO32-
IF5
ClF3
ICl4-

17. VSEPR Model
video

18. VSEPR Model
Nonbonding Electrons and Multiple Bonds can affect bond angles

19. VSEPR Model
E-ds for nonbonding electron pairs exert greater repulsive forces on adjacent e-ds and thus tend to compress bond angles

20. VSEPR Model

21. VSEPR Model
Electron domains for multiple bonds exert a greater repulsive force on adjacent electron domains than single bonds

22. VSEPR Model

23. VSEPR Model
VSEPR can be applied to larger molecules as well
The shape can be predicted around individual atoms

24. VSEPR Model

25. VSEPR Model

26. VSEPR Model

27. Sample Exercise 9.3 Predicting Bond Angles
Predict the approximate values for the H—O—C and O—C—C bond angles in vinyl alcohol .

28. Bond Polarity
a measure of how equally electrons in a bond are shared based on electronegativity

29. Dipole moment
a measure of the charge separation in a molecule

30. Dipole moment
For a molecule with more than 2 atoms, the dipole moment depends on both polarities of the bonds and the geometry of the molecule.

31. Dipole moment
For ABn molecules in which all the B atoms are the same, certain symmetrical shapes will lead to nonpolar molecules even though the individual bonds are polar

32. Dipole moment
Nonpolar symmetrical shapes are linear, trigonal planar, tetrahedral, square planar, trigonal bipyramidal, and octahedral

33. Dipole moment

34. Dipole moment

35. Dipole moment

36. Sample Exercise 9.4 Polarity of Molecules
Predict whether the following molecules are polar or nonpolar:
(a) BrCl
(b) SO2
(c) SF6
(d) NF3
(e) BCl3

37. Hybrid orbitals
Hybridization is a process that occurs when atomic orbitals mix to form new orbitals called hybrid orbitals and form bonds

38. Hybrid orbitals

39. Hybrid orbitals

40. Predicting hybridization
1. Draw lewis structure
2. Determine # e-d
3. Specify the hybrid orbitals needed to accommodate the electron pairs based on their geometric arrangement

41. Predicting hybridization
# e-d hybridization
2 sp
3 sp2
4 sp3
5 dsp3
6 d2sp3

42. Sample Exercise 9.5 Hybridization
Indicate the hybridization of orbitals employed by the central atom in
(a) NH2–
(b) SF4
(c) SO32–
(d) SF6

43. Multiple Bonds
All of the single bonds we have looked at are called sigma (s) bonds, where there is an overlap in the middle of the region of s and p orbital

44. Multiple Bonds
To describe multiple bonds, we must look at the side to side overlapping of 2 p orbitals, called a pi (p) bond

45. Multiple Bonds
A double bond is one s bond and one p bond

46. Multiple Bonds
A triple bond is one s bond and two p bonds

47. Multiple Bonds

48. Multiple Bonds
When looking at molecules that exhibit resonance there is delocalized p bonding

49. Sample Exercise 9.6 Describing  and  Bonds in a Molecule
Formaldehyde also known as ? has the following Lewis structure
Count the  and  bonds. .

50. Tell me everything you can about Acetonitrile

51. Review
PF5

52. Review
CO2

53. Review
ICl4-

54. Review
AsH3

55. Review
I3-

56. Review
SO2

57. Review
IF5

58. Review
CO32-

59. Review
SF6

60. Review
ClO4-

61. Review
OF2

62. Review
IF4+

63. Review
ClF3

64. Review
NCS-

65. Review Methanoic acid Methyl Amine Ethyne
Directions: Predict the molecular geometry, bond angle, hybridization, s and p bonds, and polar/nonpolar for the following molecule :
Methanoic acid
Methyl Amine
Ethyne