Unit 5-Chemical Bonding:
Molecular Geometry &
Polarity
VSEPR Theory:
 Valence
Shell Electron Pair
Repulsion Theory:
 Electron
pairs surrounding an
atom are oriented as far apart as
possible.
 This
results in different molecular
shapes (geometry)
VSEPR Theory
2 Types of Electron Pairs
 Bonding pairs – electrons involved in
bonding
 Lone pairs – electrons not involved in
bonding
Lone pairs repel
more strongly than
bonding pairs!!!
Determining Molecular Shape
1.
Draw the Lewis Diagram.
2.
Shape is determined by the number
of BONDING PAIRS and LONE
PAIRS.
3.
Double/triple bonds = ONE pair)
4.
Lone pairs repel more strongly than
bonding pairs so they reduce the
bond angle between atoms
1. LINEAR 180°
CO2
2 bonds total:
2 bond pairs
0 lone pairs
2. Trigonal-Planar 120°
BF3
3 total:
3 bonds
0 lone
3. Bent <120°
3 total:
2 bonds
1 lone
SnCl2
4. Tetrahedral 109.5°
4 total:
4 bonds
0 lone
CH4
5. Trigonal-Pyramidal 107°
4 total:
3 bonds
1 lone
NH3
6. Bent 104.5°
4 total:
2 bonds
2 lone
H2O
Examples
PF3
F P F
F
4 total
3 bond
1 lone
TRIGONAL
PYRAMIDAL
107°
Examples
CO2
2 total
2 bond
0 lone
O C O
LINEAR
180°
Review
1.
3
bonds
2.
3.
4.
4
bonds
5.
6.
Linear (180º)
Trigonal Planar (120°)
Bent (< 120º)
Tetrahedral (109.5°)
Trigonal Pyramidal (107°)
Bent (104.5)
Polarity
 When
a molecule
has an uneven
distribution of
electrons
 Caused by a
difference in
electronegativity
values
Polarity

Dipole Moment –an arrow that shows
the direction of the polar bond in a
molecule.

Arrow points toward the more
electronegative atom (atom with the most
electrons).
+

H
Cl

Determining Molecular Polarity
 Depends
on:
 dipole moments
 molecular shape
+

H
Cl

Determining Molecular Polarity
 Nonpolar
Molecules
 Dipole moments are symmetrical
and cancel out.
F
BF3
B
F
F
Determining Molecular Polarity
 Polar
Molecules
 Dipole moments are asymmetrical
and don’t cancel .
O
H2O
H
H
net
dipole
moment
Determining Molecular Polarity
 Therefore,
polar molecules have...
 asymmetrical shape (lone pairs) or
 asymmetrical atoms
H
CHCl3
C
Cl
Cl
Cl
net
dipole
moment