3.3 POLARITY OF MOLECULES
The polarity of a molecule is dependent on the polarity of its bonds AND the shape of the
molecule. Molecules have different shapes based on their electron arrangements. Pairs of
electrons can either be bonding pairs or lone pairs (electrons that do not participate in a bond).
The following table shows the general structure of various molecules with various electron
arrangements
Formula
AX2
Number of Number of
Bonds
Lone Pairs
2
0
Molecular
Geometry
Bond
Angle
Linear
180°
Example
Carbon Dioxide (CO2)
AX3
3
0
Triangular
Planar
120°
Boron triflouride (BF3)
AX4
4
0
Tetrahedral
109.5°
Methane (CH4)
AX3E
3
1
Trigonal
Pyramidal
109.5°
Ammonia (NH3)
AX2E2
2
2
Bent
** Yellow balls depict lone pairs of electrons
104.5°
Water (H2O)
A
end. A
distributed.
molecule has a distinct positively charged end and negatively charged
molecule has no charged ends. Its charges are equally
POLAR MOLECULES

H
Cl

A Polar molecule: Hydrogen Chloride (HCl)
Hydrogen Chloride (HCl) is
in shape. There is
bonding pair of electrons and one single bond. The one single
bond is a
bond (EN = 1.0), so the molecule
itself has a distinct positively charged end and a distinct
negatively charged in. This creates a polar molecule.
A Polar Molecule: Water (H2O)
The water molecule has a
shape. There are
________ bonding pairs of electrons and there are __________
lone pairs of electrons. Each O-H bond is
(EN=1.2) . The oxygen atom is more
and has a partial
charge and the hydrogen atom is
less
and has a partial
charge. Altogether one end (the oxygens) of the molecule has
a partial positive charge and the other end (the hydrogens)
has a partial negative charge. This creates the polar
molecule.



The polarity of water allows it to “stick together”. The partial
positive end of one water molecule attracts the partial negative end
of another water molecule. This is an
force,
because it occurs between water molecules.
What would happen if you took a negatively or positively charged
strip and brought it close to a stream of water? What would you
expect to happen and why?
NON-POLAR MOLECULES

O

C

O
A Non-Polar Molecule: Carbon Dioxide
Each C-O double bond is
(EN=0.8).
The oxygen atom is more electronegative and has a
partial negative charge and the carbon atom is less
electronegative and has a partial positive charge.
Here, the shape has more influence. The shape of
the molecule is
and is
.
The bonds are evenly distributed and cancel out
the dipoles. Symmetrical molecules are
regardless of whether the
bonds within them are polar or not. You do not see
any distinct poles on either end. Both ends are
charged.
A Non-Polar Molecule: Nitrogen Gas
The bond in a nitrogen gas molecule is a
bond
(EN=0.0). Each atom of nitrogen pulls the bonding pair of electrons
with the same strength, as there is no
.
Since the molecule is only made up of one bond, and this is a nonpolar bond, the molecule is also
. All
are considered non-polar.
N
Example 1:
Based on the shape and bond dipoles of the molecule, determine whether the following
molecules are polar or non-polar. Also, identify the shape of the molecule.
HCl, NH3, BF3, CCl4, CH3Cl
HOMEWORK: Read Page 102-108. Complete #1-6 on Page 108
Determine the VSEPR shape for question 5
N
ANSWERS TO EXAMPLE PROBLEMS