Chapter 9
Molecular Geometry and
Bonding Theories
Valence Shell Electron Pair
Repulsion (VSEPR) Theory
• based on idea that regions of electron
density in valence shell of central atom
will be distributed in space such that
electrostatic repulsions are minimized
• places regions of electron density as far
apart as possible
• produces molecular geometry
Steps in Predicting
Molecular Geometry
• draw Lewis structure of substance
• count regions of electron density on
central atom
• draw electron pair shape
• derive and draw molecular geometry
Regions of Electron Density
•
•
•
•
•
single covalent bond
double covalent bond
triple covalent bond
lone pair
unpaired electron
# Regions
2
Shape
linear
180°
# Regions
Shape
2
linear
3
trigonal planar
180°
120°
# Regions
Shape
2
linear
3
trigonal planar
4
tetrahedral
180°
120°
109.5°
90°
5
trigonal bypyramidal
120°
90°
5
trigonal bypyramidal
120°
6
octahedral
90°
Examples
Determine the electron-pair and
molecular geometries of each of the
following. Draw and name each.
Beryllium Chloride
Beryllium Chloride
BeCl2
Beryllium Chloride
BeCl2
1. Lewis structure
Beryllium Chloride
BeCl2
1. Lewis structure

Cl


Be Cl

Beryllium Chloride
BeCl2
1. Lewis structure

Cl


Be Cl

2. Count regions of electron density on
central atom
Beryllium Chloride
BeCl2
1. Lewis structure

Cl


Be Cl

2. Count regions of electron density on
central atom
2
Beryllium Chloride
BeCl2
1. Lewis structure

Cl


Be Cl

2. Count regions of electron density on
central atom
2
3. Draw and name electron-pair shape



Be Cl
Cl


linear
Beryllium Chloride
BeCl2
3. Draw and name electron-pair shape


Cl Be Cl


linear
3. Derive and name molecular shape


Cl Be Cl




linear
Carbon Dioxide
Carbon Dioxide
CO2
Carbon Dioxide
CO2

O

C

O

Carbon Dioxide
CO2

O

C

O

2 regions
Carbon Dioxide
CO2

O

C

O

2 regions
Electron-pair shape, linear

O

C

O

Carbon Dioxide
CO2

O

C

O

2 regions
Electron-pair shape, linear


O C O


Molecular shape, linear

O

C

O

Aluminum Bromide
Aluminum Bromide
AlBr3

 Br
 Br

Al
 Br

Aluminum Bromide
AlBr3

 Br
 Br

Al
Aluminum Bromide
AlBr3
3 regions
 Br


 Br
Aluminum Bromide
AlBr3
Electron-pair shape
3 regions
trigonal planar
Al
 Br  Br

 Br


 Br

Al
 Br


 Br
Aluminum Bromide
AlBr3
Electron-pair shape
3 regions
trigonal planar
Al
 Br  Br

 Br


Molecular shape
Al
trigonal planar
 Br  Br




 Br
 Br

Al
 Br

Nitrite Ion
Nitrite Ion
NO2–
   

O N O


–
Nitrite Ion
NO2–
   

O N O


3 regions
–
Nitrite Ion
NO2–
   

O N O


3 regions
–
Nitrite Ion
NO2–
Electron-pair shape
trigonal planar
–

 O

N
 O 

   

O N O


3 regions
–
Nitrite Ion
NO2–
Electron-pair shape
trigonal planar
–

 O

N
 O 

   

O N O


3 regions
Nitrite Ion
NO2–
–
Electron-pair shape
trigonal planar
Molecular shape
bent
 O


N
–
 O 

–

 O

N
 O 

Carbon Tetrabromide
Carbon Tetrabromide
CBr4



Br Br

C
 Br  Br


Carbon Tetrabromide
CBr4



Br Br

C
 Br  Br


Carbon Tetrabromide
CBr4
4 regions



Br Br

C
 Br  Br


Carbon Tetrabromide
CBr4
4 regions
Electron-pair shape
tetrahedral

Br
C
 Br
Br
   Br 




Br Br

Carbon Tetrabromide
CBr4
4 regions
C
Electron-pair shape
 Br  Br
tetrahedral




Br
Molecular shape
C
tetrahedral
 Br
Br
   Br 

Arsine
Arsine
AsH3
Arsine
AsH3
H
As
H
H
Arsine
AsH3
H
As
H
H
4 regions
electron-pair shape, tetrahedral
Arsine
AsH3
H
As
4 regions
electron-pair shape, tetrahedral
H
H

As
H
H
H
Arsine
AsH3
H
As
4 regions
electron-pair shape, tetrahedral
H
H
molecular shape
trigonal pyramid
or tripod

As
H
H
H
Arsine
AsH3
H
As
4 regions
electron-pair shape, tetrahedral
H
H
molecular shape
trigonal pyramid
or tripod

As
H
H
H
As
H
H
H
Water
H 2O
Water
H 2O
O
H
H
Water
H 2O
O
H
H
4 regions
electron-pair shape
tetrahedral
Water
H 2O
O
H
H

O
H

H
4 regions
electron-pair shape
tetrahedral
Water
H 2O
O
H
H

molecular shape
bent
O
H

4 regions
electron-pair shape
tetrahedral
H
Water
H 2O
O
H
H

molecular shape
bent
O
H

4 regions
electron-pair shape
tetrahedral
H
O
H
H
Phosphorus Pentafluoride
Phosphorus Pentafluoride
PF5

F

 
   F
F

P
 F   F
 
Phosphorus Pentafluoride
PF5
 
   F  
F
F


5 regions
P
electron-pair
shape
 F   F
trigonal bipyramidal
 
 
 F  
F
 

F

P
 F 


F

Phosphorus Pentafluoride
PF5
 
   F  
F
F


5 regions
P
electron-pair
shape
 F   F
trigonal bipyramidal
 
 
 F  
F
 

F

P
 F 


F

molecular shape
trigonal bipyramidal
Sulfur Tetrafluoride
Sulfur Tetrafluoride
SF4


F
F
    
S
 F   F
 
Sulfur Tetrafluoride
SF4


F
F
    
S
 F   F
 
Sulfur Tetrafluoride
SF4
5 regions
trigonal bipyramidal


F
F
    
S
 F   F
 
Sulfur Tetrafluoride
SF4
5 regions
trigonal bipyramidal
 
 F

F

S
 F 


F



F
F
    
S
 F   F
 
 
 F

F

S
 F 

Sulfur Tetrafluoride
SF4
5 regions
trigonal bipyramidal
molecular shape
distorted tetrahedral
 
 F

F


F

S
 F 


F



F
F
    
S
 F   F
 
 
 F

F

S
 F 

Sulfur Tetrafluoride
SF4
5 regions
trigonal bipyramidal
molecular shape
see saw
F

F

S
F
F
F
Chlorine Trifluoride
Chlorine Trifluoride
ClF3
 
F 
Cl
 F   F


Chlorine Trifluoride
ClF3
 
F 
Cl
 F   F


Chlorine Trifluoride
ClF3
5 regions
electron-pair shape
trigonal bipyramidal
Chlorine Trifluoride
ClF3
 
F 
5 regions
Cl
electron-pair shape
 F   F

trigonal bipyramidal

F


 F

Cl

F 

Chlorine Trifluoride
ClF3
 
F 
5 regions
Cl
electron-pair shape
 F   F

trigonal bipyramidal

F


 F

Cl

F 

Chlorine Trifluoride
ClF3
 
F 
5 regions
Cl
electron-pair shape
 F   F

trigonal bipyramidal

F
molecular shape
  T-shape


 F
 F
Cl



F 

F
Cl
F 

Sulfur Hexafluoride
Sulfur Hexafluoride
SF6
F

F
F
 S 


F
F
 F  
 

Sulfur Hexafluoride
SF6
Sulfur Hexafluoride
SF6
F

F
6 regions
F
 S 
electron-pair shape


F
F
octahedral
 F  
 



F 

F
F

S
F
F


F 

Sulfur Hexafluoride
SF6
F

F
6 regions
F
 S 
electron-pair shape


F
F
octahedral
 F  
 



F 
molecular shape

F
F
octahedral

S
F
F


F 

Bromine Pentafluoride
Bromine Pentafluoride
BrF5
Bromine Pentafluoride
BrF5
F 
 Br

F
 F 
 


F


F

Bromine Pentafluoride
BrF5
F 
 Br

F
 F 
 


F


F

6 regions
electron-pair shape
octahedral
Bromine Pentafluoride
BrF5
F 
 Br

F
 F 
 

F


F


F

6 regions
electron-pair shape
octahedral
F
F
Br

F


F

Bromine Pentafluoride
BrF5
F 
 Br

F
 F 
 

F


F


F

6 regions
electron-pair shape
octahedral
F
F
Br

F


F

Bromine Pentafluoride
BrF5
6 regions
F  F electron-pair shape
 Br  octahedral
molecular shape



 F
F 
square pyramidal
 F  
 



F 
F 



F



F
F
 F


Br
Br



 F

F
F



F





Xenon Tetrafluoride
Xenon Tetrafluoride
XeF4
F  F
 Xe 
F  F


Xenon Tetrafluoride
XeF4
F  F
 Xe 
F  F


Xenon Tetrafluoride
XeF4
6 regions
electron-pair shape
octahedral
Xenon Tetrafluoride
XeF4
F  F
 Xe 
F  F



F

6 regions
electron-pair shape
octahedral

F
Xe

F


F

Xenon Tetrafluoride
XeF4
F  F
 Xe 
F  F


6 regions
electron-pair shape
octahedral


F

F
Xe

F


F

Xenon Tetrafluoride
XeF4
F  F
 Xe 
F  F


6 regions
electron-pair shape
octahedral


F

F
Xe

F


F

molecular shape
square planar

F
F

Xe

F
F


Tribromide Ion
Br3–

Br

   
Br Br
 
Tribromide Ion
Br3–

Br

   
Br Br
 
Tribromide Ion
Br3–
5 regions
electron-pair shape
trigonal bipyramidal

Br

Tribromide Ion
Br3–
   
Br Br
 
5 regions
electron-pair shape
trigonal bipyramidal


Br


Br
 Br



Br

Tribromide Ion
Br3–
   
Br Br
 
5 regions
electron-pair shape
trigonal bipyramidal


Br


Br
 Br



Br

Tribromide Ion
Br3–
   
Br Br
 
5 regions
electron-pair shape
trigonal bipyramidal


Br
molecular shape
linear


Br
 Br


 
Br
Br
 Br

Polarity of Molecules
• molecules in which dipole moments
of the bonds do not cancel are polar
molecules
• molecules that do not contain polar
bonds or in which all dipole
moments cancel are non-polar
molecules
CO2
O
C
O
vs
H2O
O
H
H
CO2
–
O
+
C
–
O
vs
H2O
–
O
H
+
H
+
CO2
–
O
+
C
–
O
vs
H2O
–
O
H
+
H
+
CO2
–
O
+
C
0
–
O
vs
H2O
–
O
H
+
H
+
CO2
–
O
+
C
0
–
O
vs
H2O
–
O
H
+
H
+
CO2
vs
H2O
H
+
–
O
+
C
–
O
y
–
O
H
+
x
y
0
x
CO2
vs
H2O
–
O
H
+
H
+
–
O
+
C
–
O
y
y
x
x
CO2
–
O
+
C
–
O
nonpolar
vs
H2O
–
O
H
+
H
+
polar
Study and Know
9.2 Polarity of Molecules
VSEPR Theory only explains molecular
shapes
says nothing about bonding in
molecules
Enter Valence Bond (VB) Theory
atoms share electron pairs by allowing
their atomic orbitals to overlap
+
H
H
+
H
H
 bond
+
H
H
E
1s
H
 bond
+
H
H
E
H
1s
H
 bond
+
F
F
F2
+
F
F
F2
 bond
2p
E
2s
1s
F
F
2p
E
2s
1s
F
Methane
CH4
2p
E
2s
1s
C
Methane
CH4
H
H
2p
E
2s
1s
C
Methane
CH4
H
H+
E
2p
2s
1s
H
C
Methane
CH4
H
H+
E
2p
2s
1s
H H–
C
Methane
CH4
H
H+
E
H H–
2p
H
2s
H
C
C
H
90°
H
1s
90°
Methane
CH4
H
109.5°
C
H
H
H
Tetrahedral Geometry
4 Identical Bonds
Problem and Solution
C must have 4 identical orbitals in
valence shell for bonding
solution: hybridization
Methane
CH4
2p
E
2s
1s
Methane
CH4
2s
2p
E
2s
1s
E
1s
2p
Methane
CH4
2s
2p
E
2s
1s
E
1s
2p
Methane
CH4
2s
2p
E
2s
1s
E
1s
2p
Methane
CH4
2p
E
2s
1s
sp3
E
1s
+
–
+
+
2p
2s
+
–
+
+
2p
=
2s
an sp3 hybrid orbital
4 identical sp3 hybrid orbitals
4 identical sp3 hybrid orbitals
tetrahedral geometry
4 identical sp3 hybrid orbitals
tetrahedral geometry
4 identical sp3 hybrid orbitals
tetrahedral geometry
Methane
CH4
H
2p
E
2s
1s
H
H
sp3
E
1s
H
Hybridization vs Shape (e– pair)
•
•
•
•
•
sp
sp2
sp3
sp3d
sp3d2
linear
trigonal planar
tetrahedral
trigonal bipyramidal
octahedral
Predict the Hybridization of the Central Atom
in tribromide ion
Predict the Hybridization of the Central Atom
in tribromide ion
Br3–
Predict the Hybridization of the Central Atom
in tribromide ion
Br3–


Br

   
Br Br 
 
5 regions
electron-pair shape
trigonal bypyramidal
Predict the Hybridization of the Central Atom
in tribromide ion
Br3–


Br

   
Br Br
 
5 regions
electron-pair shape
trigonal bypyramidal
sp3d
Predict the Hybridization of the Central Atom
in carbon dioxide
CO2
Predict the Hybridization of the Central Atom
in carbon dioxide
CO2


O C O


2 regions
Electron-pair shape, linear
Predict the Hybridization of the Central Atom
in carbon dioxide
CO2


O C O


2 regions
Electron-pair shape, linear
sp
Predict the Hybridization of the Central Atom
in aluminum bromide
Predict the Hybridization of the Central Atom
in aluminum bromide

 Br
 Br

Al
 Br

Electron-pair shape
3 regions
trigonal planar
Predict the Hybridization of the Central Atom
in aluminum bromide

 Br
 Br

Al
 Br

Electron-pair shape
3 regions
trigonal planar
sp2
Predict the Hybridization of the Central Atom
in xenon tetrafluoride
Predict the Hybridization of the Central Atom
in xenon tetrafluoride




 F  F
 Xe 




F
F


6 regions
electron-pair shape
octahedral
Predict the Hybridization of the Central Atom
in xenon tetrafluoride




 F  F
 Xe 




F
F


6 regions
electron-pair shape
octahedral
sp3d2
Consider Ethylene, C2H4
Consider Ethylene, C2H4
H
H
C
H
C
H
Consider Ethylene, C2H4
H
H
C
C
H
3 regions
trigonal planar
H
Consider Ethylene, C2H4
H
H
C
C
H
3 regions
trigonal planar
sp2
H
Consider Ethylene, C2H4
H
H
C
H
C
H
3 regions
trigonal planar
2
sp
2p
E
2s
1s
2s
2p
E
2s
1s
E
1s
2p
2p
E
2s
1s
sp2
E
1s
2p
sp2
2p
sp2
sp2
2p
sp2
sp2
sp2
 bond framework
 bond
 bond
Consider Acetylene, C2H2
H
C
C
H
Consider Acetylene, C2H2
H
C
2 regions
linear
C
H
Consider Acetylene, C2H2
H
C
C
2 regions
linear
sp
H
Consider Acetylene, C2H2
H
C
C
H
2 regions
linear
sp
2s
2p
E
2s
1s
E
1s
2p
2p
E
2s
1s
sp
E
1s
2p
2p
sp
2p
sp
 bond framework
 bonds
 bonds
Generally
• single bond is a  bond
• double bond consists of 1  and 1 
bond
• triple bond consists of 1  and 2 
bonds
Molecular Orbital (MO) Theory
when atoms combine to form molecules,
atomic orbitals overlap and are then
combined to form molecular orbitals
orbitals are conserved
a molecular orbital is an orbital associated
with more than 1 nucleus
like any other orbital, an MO can hold 2
electrons
consider hydrogen atoms bonding to form
H2
+
H
H
subtract
add
subtract
antibonding
add
bonding
subtract
antibonding
*1s
add
bonding 1s
*1s
E
E
1s
1s
1s
H
H2
H
*1s
E
E
1s
1s
1s
H
H2
H
*1s
E
E
1s
1s
1s
H
H2
H
*1s
E
E
1s
1s
1s
H
H2
H
(1s ) 2
*1s
E
E
1s
1s
1s
H
H2
H
(1s ) 2
total spin = 0
*1s
E
E
1s
1s
1s
H
H2
H
• Diamagnetic: slightly repelled by a
magnetic field
total spin = 0
• paramagnetic: attracted to a
magnetic fiels
total spin not 0
• Bond Order = 1/2 (bonding e– –
antibonding e–)
(1s ) 2
total spin = 0
diamagnetic
*1s
E
E
1s
1s
1s
H
H2
H
BO = 1/2 ( 2 – 0) = 1
*1s
E
E
1s
1s
1s
H
H2
H
Consider He2
*1s
E
E
1s
1s
1s
He
He2
He
*1s
E
E
1s
1s
1s
He
He2
He
(1s ) 2 ( *1s ) 2
*1s
E
E
1s
1s
1s
He
He2
He
diamagnetic
*1s
E
E
1s
1s
1s
He
He2
He
BO = 1/2 ( 2 – 2 ) = 0
*1s
E
E
1s
1s
1s
He
He2
He
Combination of p Atomic
Orbitals
2p
2p
subtract
add
antibonding MO
subtract
add
bonding MO
subtract
antibonding MO
 *2p
add
bonding MO
 2p
2p
2p
subtract
add
subtract
antibonding MO
add
bonding MO
subtract
*2p
add
2p
subtract
*2p
add
2p
Consider Li2
*2p
*2p
2p
E
2p
2p
E
2p
*2s
2s
2s
Li
2s
Li2
Li
*2p
*2p
2p
E
2p
2p
E
2p
*2s
2s
2s
Li
2s
Li2
Li
*2p
*2p
2p
E
2p
2p
E
2p
*2s
2s
2s
Be
2s
Be2
Be
*2p
*2p
2p
E
2p
2p
E
2p
*2s
2s
2s
Be
2s
Be2
Be
*2p
*2p
2p
E
2p
2p
E
2p
*2s
2s
2s
B
2s
B2
B
*2p
*2p
2p
E
2p
2p
E
2p
*2s
2s
2s
B
2s
B2
B
*2p
*2p
2p
E
2p
2p
E
2p
*2s
2s
2s
C
2s
C2
C
*2p
*2p
2p
E
2p
2p
E
2p
*2s
2s
2s
N
2s
N2
N
*2p
*2p
2p
E
2p
2p
E
2p
*2s
2s
2s
O
2s
O2
O
*2p
*2p
2p
E
2p
2p
E
2p
*2s
2s
2s
F
2s
F2
F
*2p
*2p
2p
E
2p
2p
E
2p
*2s
2s
2s
Ne
2s
Ne2
Ne