1. Chapter 10 Chemical Bonding II
Chemistry II
Chapter 10 Chemical Bonding II

2. Chemical Bonding II Molecular Shapes

3. Chemical Bonding II Molecular Shapes
From the model of EDTA we can infer that the 3-Dimensional structure of a molecule determines its __________
the structure displays many molecular properties:
Skeletal structure
Bonding
Shape
Bond theory allows you to predict the shapes of molecules
properties

4. Chemical Bonding II VSEPR Theory
e- groups (lone pairs and bonds) are most stable when they are as far apart as possible –
v________ s____ e_______ p_____ r_________ theory
Maximum separation
3-D representation allows us to predict the shapes and bond angles in the molecule
Valence shell electron pair repulsion

5. Chemical Bonding II VSEPR Theory
e.g. draw the 2 possible Lewis dot structures for NO2- and discuss the behavior of the associated e- groups
there are 3 e- groups on N
1 lone pair
1 single bond
1 double bond (counted as 1 group)
there are _____ e- groups on N
____ lone pair
____ single bond
____ double bond (counted as 1 group)

6. Chemical Bonding II 2 e- Groups: Linear Geometry
5 basic shapes of molecules:
linear,
trigonal planar,
tetrahedral,
trigonal bipyramidal,
octahedral
Also draw BeCl2, bond angles are 180 degrees

7. Chemical Bonding II 2 e- Groups: Linear Geometry
Draw both 2-dimensional and 3-dimensional pictures of the molecules in the following slides

8. Chemical Bonding II 2 e- Groups: Linear Geometry
occupy positions opposite, around the central atom
linear geometry - bond angle is ________
e.g. CO2
Also draw BeCl2, bond angles are 180 degrees

9. Chemical Bonding II 3 e- Groups: Trigonal Geometry
occupy triangular positions
trigonal planar geometry - bond angle is __________
e.g. BF3
BF3, 120 degree bond angles

10. Chemical Bonding II 3 e- Groups: Trigonal Geometry
e.g. Formaldehyde, CH2O
3 e– groups around central atom – why not 120° ?

11. Chemical Bonding II 4 e- Groups: Tetrahedral Geometry
occupy tetrahedron positions around the central atom
tetrahedral geometry - bond angle is ________
e.g. CH4
109.5

12. Chemical Bonding II 5 e- Groups: Trigonal Bipyramidal Geometry
occupy positions in the shape of a two tetrahedra that are base-to-base
trigonal bipyramidal geometry
e.g. PCl5

13. Chemical Bonding II 6 e- Groups: Octahedral Geometry
occupy positions in the shape of two square-base pyramids that are base-to-base
octahedral geometry
e.g. SF6

14. Chemical Bonding II The Effect of Lone Pairs
lone pair groups “occupy more space” on the central atom
relative sizes of repulsive force interactions is:
Lone Pair – Lone Pair > Lone Pair – Bonding Pair > Bonding Pair – Bonding Pair
this effects the bond angles, making them smaller than expected

15. Chemical Bonding II 3 e- Groups with Lone Pairs: Derivative of Trigonal Geometry
when there are 3 e- groups around central atom, and 1 of them is a lone pair trigonal planar - bent shape - bond angle < 120°
e.g. SO2
S has 6, O has 6 electrons. Double bond O to S, single bond O to S, S has lone pair…resonance hybrid

16. Chemical Bonding II 4 e- Groups with Lone Pairs : Derivatives of Tetrahedral Geometry
when there are 4 e- groups around the central atom, and 1 is a lone pair trigonal pyramidal shape – bond angle is 107 °
e.g. NH3

17. Which species has the smaller bond angle, Perchlorate (ClO4-) or Chlorate (ClO3-)?

18. Chemical Bonding II 4 e- Groups with Lone Pairs: Derivatives of Tetrahedral Geometry
when there are 4 e- groups around the central atom, and 2 are lone pairs tetrahedral-bent shape – bond angle is °
e.g. H2O

19. Chemical Bonding II Tetrahedral-Bent Shape

21. Chemical Bonding II 5 e- Groups with Lone Pairs Derivatives of Trigonal Bipyramidal Geometry
when there are 5 e- groups around the central atom, and some are lone pairs, they will occupy the equatorial positions because there is more room
when there are 5 e- groups around the central atom, and 1 is a lone pair, the result is called see-saw shape
aka distorted tetrahedron
when there are 5 e- groups around the central atom, and 2 are lone pairs, the result is called T-shaped
when there are 5 e- groups around the central atom, and 3 are lone pairs, the result is called a linear shape
the bond angles between equatorial positions is < 120°
the bond angles between axial and equatorial positions is < 90°
linear = 180° axial-to-axial

22. Chemical Bonding II Replacing Atoms with Lone Pairs in the Trigonal Bipyramid System

23. Chemical Bonding II See-Saw Shape

24. Chemical Bonding II T-Shape

25. Chemical Bonding II Linear Shape
Tro, Chemistry: A Molecular Approach

26. Chemical Bonding II 6 e- Groups with Lone Pairs: Derivatives of Octahedral Geometry
when there are 6 e- groups around the central atom, and 1 is a lone pair, the result is called a square pyramid shape
the bond angles between axial and equatorial positions is < 90°

27. 6 e- Groups with Lone Pairs Derivatives of Octahedral Geometry
when there are 6 e- groups around the central atom, and 2 are lone pairs, the result is called a square planar shape
the bond angles between equatorial positions is 90°

29. Chemical Bonding II Predicting the Shapes Around Central Atoms
1. Draw the Lewis Structure
2. Determine the Number of Electron Groups around the Central Atom
3. Classify Each Electron Group as Bonding or Lone pair, and Count each type
remember, multiple bonds count as 1 group
4. Use Table 10.1 to Determine the Shape and Bond Angles

30. Practice – Predict the Molecular Geometry and Bond Angles in SiF5-

31. Practice – Predict the Molecular Geometry and Bond Angles in SiF5─-
Si Least Electronegative
5 Electron Groups on Si
Si Is Central Atom
5 Bonding Groups
0 Lone Pairs
Si = 4e─
F5 = 5(7e─) = 35e─
(─) = 1e─
total = 40e─
Shape = Trigonal Bipyramid
Bond Angles
Feq-Si-Feq = 120°
Feq-Si-Fax = 90°

32. Practice – Predict the Molecular Geometry and Bond Angles in ClO2F (Chloryl Fluoride)

33. Practice – Predict the Molecular Geometry and Bond Angles in ClO2F
Cl Least Electronegative
4 Electron Groups on Cl
Cl Is Central Atom
3 Bonding Groups
1 Lone Pair
Cl = 7e─
O2 = 2(6e─) = 12e─
F = 7e─
Total = 26e─
Shape = Trigonal Pyramidal
Bond Angles
O-Cl-O < 109.5°
O-Cl-F < 109.5°

34. Chemical Bonding II Representing 3-Dimensional Shapes on a 2-Dimensional Surface
one of the problems with drawing molecules is trying to show their dimensionality
by convention, the central atom is put in the plane of the paper
put as many other atoms as possible in the same plane and indicate with a straight line
for atoms in front of the plane, use a solid wedge
for atoms behind the plane, use a hashed wedge

36. SF6 S F

38. Multiple Central Atoms
many molecules have larger structures with many interior atoms
we can think of them as having multiple central atoms
when this occurs, we describe the shape around each central atom in sequence e.g. acetic acid
shape around left C is tetrahedral
shape around center C is trigonal planar
shape around right O is tetrahedral-bent

39. Describing the Geometry of Methanol

40. Describing the Geometry of Glycine

41. Practice – Predict the Molecular Geometries in H3BO3
Tro, Chemistry: A Molecular Approach

42. Practice – Predict the Molecular Geometries in H3BO3
oxyacid, so H attached to O
3 Electron Groups on B
4 Electron Groups on O
B Least Electronegative
O has
2 Bonding Groups
2 Lone Pairs
B has
3 Bonding Groups
0 Lone Pairs
B Is Central Atom
B = 3e─
O3 = 3(6e─) = 18e─
H3 = 3(1e─) = 3e─
Total = 24e─
Shape on B = Trigonal Planar
Shape on O = Bent

43. Practice – Predict the Molecular Geometries in C2H4
Tro, Chemistry: A Molecular Approach

44. Practice – Predict the Molecular Geometries in C2H4
3 Electron Groups on C
C = 2(4e─) = 8e ─
H = 4(1e─) = 4e─
Total = 12e─
0 Lone Pairs
Shape on each C = Trigonal Planar

45. Practice – Predict the Molecular Geometries in CH3OCH3

46. Practice – Predict the Molecular Geometries in Dimethyl Ether (CH3OCH3)
4 Electron Groups on C
C = 2(4e─) = 8e ─
H = 6(1e─) = 6e─
O = 6(1e─) = 6e─
Total = 20e─
2 Lone Pairs on O
Shape on each C = Tetrahedral
Shape on O = Bent

47. Reminder about Eletronegativity!
Electronegativity, is a chemical property that describes the tendency of an atom to e- towards itself

48. Polarity of Molecules in order for a molecule to be polar it must
have polar bonds
electronegativity difference
dipole moments (charge x distance)
have an unsymmetrical shape
vector addition
polarity affects the intermolecular forces of attraction
therefore boiling points and solubilities
like dissolves like
nonbonding pairs strongly affect molecular polarity

49. Molecule Polarity The H-Cl bond is polar
Bonding e- are pulled toward the Cl end of the molecule
Net result is a polar molecule.

50. Vector Addition

52. Molecule Polarity The O-C bond is polar
The bonding e- are pulled equally toward both O’s
Symmetrical molecule
Net result is a nonpolar molecule

53. Molecule Polarity
The H-O bond is polar Both sets of bonding e- are pulled toward the O
Net result is a polar molecule

54. Molecule Polarity

55. Molecule Polarity The H-N bond is polar
All the sets of bonding electrons are pulled toward the N
Not symmetrical
Net result is a polar molecule

56. Molecule Polarity The C-H bond is polar
Four equal dipoles cancel each other out due to symmetry
Net result is a non-polar molecule

57. Molecular Polarity Affects Solubility in Water
polar molecules are attracted to other polar molecules
since water is a polar molecule, other polar molecules dissolve well in water
and ionic compounds as well

58. Molecular Polarity Affects Solubility in Water
Oil and water do not mix!
Mutual attraction causes polar molecules to clump together

59. Unique Properties Water shrinks on melting (ice floats on water)
Unusually high melting point
Unusually high boiling point
Unusually high surface tension
Unusually high viscosity
Unusually high heat of vaporization
Unusually high specific heat capacity
And more…

60. Molecular Polarity Affects Solubility in Water
some molecules have both polar and nonpolar parts e.g. soap

61. Practice - Decide Whether the Following Are PolarEN
O = 3.5
N = 3.0
Cl = 3.0
S = 2.5
Nitrosyl chloride

62. Practice - Decide Whether the Following Are Polar
Trigonal
Bent Cl N O
3.0
3.5
Trigonal
Planar O S
3.5
2.5
1) polar bonds, N-O
2) asymmetrical shape
1) polar bonds, all S-O
2) symmetrical shape
polar
nonpolar