Chapter 9
Molecular Geometry
Molecular Shapes
 Lewis
Structures do not
account for shape of
molecules rather they only
show the number and types
of bonds between atoms
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
Molecular Shapes
 We
will focus on atoms with
ABn format, a central atom A
has n B atoms bonded to it
Molecular Shapes
VSEPR Model
 An
electron domain consists
of nonbonding pairs, single
bonds, or multiple bonds
VSEPR Model
VSEPR Model
 Electron
domains are
negatively charged, so they
repel each other, and stay
out of each other’s way
VSEPR Model
 the
best arrangement of a
given number of electron
domains is the one that
minimizes the repulsions
among them
VSEPR Model
 The
shape of the substance
in the ABn format depends
on the number of electron
domains surrounding the
central atom (Electrondomain geometry)
VSEPR Model
 Molecular
shape describes
the arrangement of atoms,
not the electron domains
(molecular geometry)
VSEPR Model
 To
Predict Shapes:
 1. Draw Lewis structure and
count e-d
 2. Determine e-d geometry
 3. Predict molecular
geometry
VSEPR Model
 See
table
VSEPR Model
Domain
s
Basic Geometry
0 lone pairs
1 lone pair
2 lone pairs
3 lone pairs
2
Linear
3
trigonal planar
bent
tetrahedral
trigonal pyramidal
bent
trigonal bipyramidal
seesaw
T-shaped
octahedral
square pyramidal
square planar
4
5
6
linear
VSEPR Model
Sample Ex. 8.1-8.2








Use VSEPR to predict shape for the following
substances:
O3
SnCl3SeCl2
CO32IF5
ClF3
ICl4-
VSEPR Model
 video
VSEPR Model
 Nonbonding
Electrons and
Multiple Bonds can affect
bond angles
VSEPR Model
 E-ds
for nonbonding electron
pairs exert greater repulsive
forces on adjacent e-ds and
thus tend to compress bond
angles
VSEPR Model
VSEPR Model
 Electron
domains for multiple
bonds exert a greater
repulsive force on adjacent
electron domains than single
bonds
VSEPR Model
VSEPR Model
 VSEPR
can be applied to
larger molecules as well
 The shape can be predicted
around individual atoms
VSEPR Model
VSEPR Model
VSEPR Model
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
Bond Polarity
a
measure of how equally
electrons in a bond are
shared based on
electronegativity
Dipole moment
a
measure of the charge
separation in a molecule
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.
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
Dipole moment
 Nonpolar
symmetrical shapes
are linear, trigonal planar,
tetrahedral, square planar,
trigonal bipyramidal, and
octahedral
Dipole moment
Dipole moment
Dipole moment
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
Hybrid orbitals
 Hybridization
is a process
that occurs when atomic
orbitals mix to form new
orbitals called hybrid orbitals
and form bonds
Hybrid orbitals
Hybrid orbitals
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
Predicting hybridization
# e-d
2
3
4
5
6
hybridization
sp
sp2
sp3
dsp3
d2sp3
Sample Exercise 9.5
Hybridization
Indicate the hybridization of orbitals
employed by the central atom in
 (a) NH2–
 (b) SF4
 (c) SO32–
 (d) SF6

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 orbitals.
Multiple Bonds
 To
describe multiple bonds,
we must look at the side to
side overlapping of 2 p
orbitals, called a pi (p) bond
Multiple Bonds
double bond is one s bond
and one p bond
A
Multiple Bonds
triple bond is one s bond
and two p bonds
A
Multiple Bonds
Multiple Bonds
 When
looking at molecules
that exhibit resonance there
are delocalized p bonding
Sample Exercise 9.6
Describing s and p Bonds in a
Molecule
Formaldehyde also known as ? has the
following Lewis structure
.
Count the s and p bonds.
Tell me everything you can about
Acetonitrile
Review
PF5
Review
CO2
Review
ICl4
-
Review
AsH3
Review
I3
-
Review
SO2
Review
IF5
Review
CO3
2-
Review
SF6
Review
ClO4
Review
OF2
Review
IF4
+
Review
ClF3
Review
NCS
Review
Directions: Predict the molecular
geometry, bond angle, hybridization, s
and p bonds, and polar/nonpolar for the
following molecule :
Methanoic acid
Methyl Amine
Ethyne