CHAPTER TEN
CHEMICAL BONDING II:
MOLECULAR GEOMETRY AND
HYBRIDIZATION OF ATOMIC
ORBITALS
MOLECULAR GEOMETRY
V
S
E
P
R

VSEPR Theory
In VSEPR theory, multiple bonds behave like a
single electron pair
MOLECULAR GEOMETRY
Valence shell electron pair repulsion (VSEPR) model:
Predict the geometry of the molecule from the electrostatic repulsions
between the electron (bonding and nonbonding) pairs.
Class
# of atoms
bonded to
central atom
# lone
pairs on
central atom
AB2
2
0
Arrangement of
electron pairs
Molecular
Geometry
B
B
1
Cl
Be
Cl
MOLECULAR GEOMETRY
Class
# of atoms
bonded to
central atom
# lone
pairs on
central atom
Arrangement of
electron pairs
AB2
2
0
linear
AB3
3
0
Molecular
Geometry
linear
2
MOLECULAR GEOMETRY
Class
# of atoms
bonded to
central atom
# lone
pairs on
central atom
AB2
2
0
linear
linear
trigonal
planar
trigonal
planar
AB3
3
0
AB4
4
0
Arrangement of
electron pairs
Molecular
Geometry
MOLECULAR GEOMETRY
Class
# of atoms
bonded to
central atom
# lone
pairs on
central atom
AB2
2
0
linear
linear
trigonal
planar
tetrahedral
Arrangement of
electron pairs
AB3
3
0
trigonal
planar
AB4
4
0
tetrahedral
AB5
5
0
Molecular
Geometry
3
MOLECULAR GEOMETRY
Class
# of atoms
bonded to
central atom
# lone
pairs on
central atom
AB2
2
0
linear
linear
trigonal
planar
Arrangement of
electron pairs
Molecular
Geometry
AB3
3
0
trigonal
planar
AB4
4
0
tetrahedral
tetrahedral
trigonal
bipyramidal
trigonal
bipyramidal
AB5
5
0
AB6
6
0
4
MOLECULAR GEOMETRY
Class
# of atoms
bonded to
central atom
# lone
pairs on
central atom
AB3
3
0
AB2 E
2
1
Arrangement of
electron pairs
Molecular
Geometry
trigonal
planar
trigonal
planar
trigonal
planar
5
MOLECULAR GEOMETRY
Class
# of atoms
bonded to
central atom
# lone
pairs on
central atom
AB4
4
0
tetrahedral
AB3 E
3
1
tetrahedral
Arrangement of
electron pairs
Molecular
Geometry
tetrahedral
MOLECULAR GEOMETRY
Class
# of atoms
bonded to
central atom
# lone
pairs on
central atom
AB4
4
0
tetrahedral
tetrahedral
AB3 E
3
1
tetrahedral
trigonal
pyramidal
AB2 E2
2
2
tetrahedral
Arrangement of
electron pairs
Molecular
Geometry
O
H
H
MOLECULAR GEOMETRY
Class
# of atoms
bonded to
central atom
# lone
pairs on
central atom
AB5
5
0
trigonal
bipyramidal
AB4 E
4
1
trigonal
bipyramidal
Arrangement of
electron pairs
Molecular
Geometry
trigonal
bipyramidal
6
MOLECULAR GEOMETRY
Class
# of atoms
bonded to
central atom
# lone
pairs on
central atom
AB5
5
0
AB4 E
4
1
AB3 E2
3
2
Arrangement of
electron pairs
Molecular
Geometry
trigonal
bipyramidal
trigonal
bipyramidal
trigonal
bipyramidal
trigonal
bipyramidal
distorted
tetrahedron
F
F
Cl
F
MOLECULAR GEOMETRY
Class
# of atoms
bonded to
central atom
# lone
pairs on
central atom
AB5
5
0
AB4 E
4
1
AB3 E2
3
2
AB2 E3
2
3
I
I
Arrangement of
electron pairs
Molecular
Geometry
trigonal
bipyramidal
trigonal
bipyramidal
trigonal
bipyramidal
trigonal
bipyramidal
distorted
tetrahedron
T-shaped
trigonal
bipyramidal
I
MOLECULAR GEOMETRY
Class
# of atoms
bonded to
central atom
# lone
pairs on
central atom
AB6
6
0
octahedral
AB5 E
5
1
octahedral
Arrangement of
electron pairs
Molecular
Geometry
octahedral
F
F
F
Br
F
F
7
MOLECULAR GEOMETRY
Class
# of atoms
bonded to
central atom
# lone
pairs on
central atom
AB6
6
0
octahedral
octahedral
AB5 E
5
1
octahedral
square
pyramidal
AB4 E2
4
2
octahedral
Arrangement of
electron pairs
Molecular
Geometry
F
F
Xe
F
F
10.1
MOLECULAR GEOMETRY
Predicting Molecular Geometry
1. Draw Lewis structure for molecule.
2. Count number of lone pairs on the central atom and
number of atoms bonded to the central atom.
3. Use VSEPR to predict the geometry of the molecule.
What are the molecular geometries of SO2 and SF4?
8
DIPOLE MOMENTS
Bonds and molecules may be polar or
nonpolar
 Relative to distribution of electrons
 Dipole moment (µ= Q x r)
 Bonds


Molecule
DIPOLE MOMENTS
Dipole Moments and Polar Molecules
electron poor
region
electron rich
region
H
F
δ+
δ-
DIPOLE MOMENTS
H2O vs CO2
BF3 vs NH3
 cis-C2H2Cl2 vs trans- C2H2Cl2


9
DIPOLE MOMENTS
H2O vs CO2
 BF3 vs NH3
 cis-C2H2Cl2 vs trans- C2H2Cl2
 NH3 vs NF3

10.2
10
DIPOLE MOMENTS
Does CH2Cl2 have
a dipole moment?
VALENCE BOND THEORY
Change in electron density
as two hydrogen atoms
approach each other.
11
VALENCE BOND THEORY
Covalent bond consists of pair of electrons
of opposite spin within an AO
 Appears that to form bond, must have
unpaired electron
 New AO--hybrid orbital
 Mix AO before bonding occurs
 Explains # of bonds and bond angles

VALENCE BOND THEORY
Hybridization – mixing of two or more atomic orbitals to
form a new set of hybrid orbitals.
1. Mix at least 2 nonequivalent atomic orbitals (e.g. s and p). Hybrid
orbitals have very different shape from original atomic orbitals.
2. Number of hybrid orbitals is equal to number of pure atomic
orbitals used in the hybridization process.
3. Covalent bonds are formed by:
a. Overlap of hybrid orbitals with atomic orbitals
b. Overlap of hybrid orbitals with other hybrid orbitals
12
VALENCE BOND THEORY
Draw Lewis Structure
 Count valence electron pairs (multiples = 1)
 # valence pairs = # hybrid orbitals (Table 10.4)

VALENCE BOND THEORY
Ground state orbital diagram (valence)
Excitation
 Hybridization
 CH4,


13
What about NH3?
14
VALENCE BOND THEORY
Ground state orbital diagram (valence)
 Excitation
 Hybridization
 BF3 ,

Formation of sp2 Hybrid Orbitals
VALENCE BOND THEORY
Ground state orbital diagram (valence)
Excitation
 Hybridization
 BeCl2,


15
Formation of sp Hybrid Orbitals
VALENCE BOND THEORY
Ground state orbital diagram (valence)
 Excitation
 Hybridization
 SF6,

HYBRIDIZATION OF
MULTIPLE BONDS

Extra electrons not located in hybrid orbitals
Sigma Bond

Pi Bond

16
HYBRIDIZATION OF
MULTIPLE BONDS


C2H4 (Lewis Structure)
Each C is
HYBRIDIZATION OF
MULTIPLE BONDS


C2H4 (Lewis Structure)
Each C is
17
HYBRIDIZATION OF
MULTIPLE BONDS


C2H2 (Lewis Structure)
Each C is
HYBRIDIZATION OF
MULTIPLE BONDS
18
HYBRIDIZATION OF
MULTIPLE BONDS
Sigma (σ) and Pi Bonds (π)
Single bond
Double bond
Triple bond
How many σ and π bonds are in the acetic acid
(vinegar) molecule CH3COOH?
σ bonds =
π bonds =
19