Molecular Geometry and
Bonding Theories
AP Chemistry – Ch 9
Mr. Christopherson
VSEPR Theory
Valence Shell Electron Pair Repulsion
Theory
Electron pairs orient themselves around
the central atom in order to minimize
repulsive forces. They get as far apart
from each other as possible.
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VSEPR Theory
Types of e- Pairs
Bonding pairs - form bonds
Lone pairs - nonbonding electrons
Lone pairs repel
more strongly than
bonding pairs!!!
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VSEPR Theory
Lone pairs reduce the bond angle
between atoms because they repel
more strongly than bonding pairs.
Bond Angle
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Determining Molecular Shape
Draw the Lewis Diagram.
Count up e- pairs on central atom.
double/triple bonds = ONE pair
Shape is determined by the # of
bonding pairs and lone pairs.
Know the 8 common shapes
& their bond angles!
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Molecular Shapes
AB2
Linear
AB4
Tetrahedral
AB3
Trigonal planar
AB3E
Angular or Bent
AB3E
Trigonal
pyramidal
AB2E2
Angular
or Bent
The VSEPR Model
The Shapes of Some Simple ABn Molecules
SO2
..
O
N
S
O
C
O
O
Linear
O
Bent
F
S
O
F
F
O
Trigonal
planar
Trigonal
pyramidal
SF6
F
F
F
F
F
Square
planar
Brown, LeMay, Bursten, Chemistry The Central Science, 2000, page 305
F
F
P
Xe
F
F
F
S
F
F
F
F
F
Trigonal
bipyramidal
Octahedral
Bonding and Shape of Molecules
Number
of Bonds
Number of
LONE Pairs
0
3
0
4
0
3
1
2
2
Shape
Examples
-Be-
Linear
BeCl2
Trigonal planar
BF3
Tetrahedral
CH4, SiCl4
Pyramidal
NH3, PCl3
Bent
H2O, H2S, SCl2
B
C
:
2
Covalent
Structure
:
N
O:
Molecular Geometry
180o
109.5o
Trigonal planar
Linear
Tetrahedral
107.3o
Trigonal pyramidal
104.5o
Bent
H2O CH4 PCl3
BeH2
BF3 CO2
H
H
CH4
H
C
H
H
molecular
formula
structural
formula
H
C
109.5o
H
H
molecular
shape
H
C
H
H
H
tetrahedral
shape of
methane
tetrahedron
ball-and-stick
model
Methane & Carbon Tetrachloride
molecular
formula
structural
formula
molecular
shape
H
CH4
H
C
ball-and-stick
model
H
H
H
H
C
109.5o
H
H
Cl
CCl4
Cl
C
Cl
Cl
space-filling model
H
H
..
..
C
N
O
109.5o
H
H
H
CH4, methane
lone pair
electrons
107o
H
H
104.5o
H
NH3, ammonia
H2O, water
..
O
O
O
O
O3, ozone
H
O
O
Common Molecular Shapes
2 total
2 bond
0 lone
B
A
B
LINEAR
BeH2
180°
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Examples
 CO2
2 total
2 bond
0 lone
O C O
LINEAR
180°
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Common Molecular Shapes
3 total
3 bond
0 lone
B
A
B
B
BF3
TRIGONAL PLANAR
120°
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Common Molecular Shapes
3 total
2 bond
1 lone
SO2
BENT
<120°
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Common Molecular Shapes
4 total
4 bond
0 lone
B
A
B
B
B
CH4
TETRAHEDRAL
109.5°
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Common Molecular Shapes
4 total
3 bond
1 lone
NH3
TRIGONAL PYRAMIDAL
107°
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Examples
 PF3
4 total
3 bond
1 lone
F P F
F
TRIGONAL
PYRAMIDAL
107°
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Common Molecular Shapes
4 total
2 bond
2 lone
H2O
BENT
104.5°
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Common Molecular Shapes
Ba
5 total
5 bond
0 lone
Be
Be
Be
Ba
PCl5
TRIGONAL
BIPYRAMIDAL
120°/90°
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Common Molecular Shapes
6 total
6 bond
0 lone
B
B
A
B
B
B
B
SF6
OCTAHEDRAL
90°
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