Molecule
has no
certain
shape or
geometry.
BLUFF
There are millions
of different
molecules, and there
are many ways to
sort them. One way
to classify them is
based on polarity.
FACT
Two factors
that determine
the polarity of
molecules
refers to the ability of an
atom to attract shared
electrons in a covalent
bond.
𝐍𝐇𝟑
Remember:
Elements with the
higher EN value
become the partial
negative pole, while
elements with the lower
EN value become the
partial positive pole.
This makes the
molecule a polar
molecule.
occur when electrons are
shared equally between
two atoms.
1. 𝐇𝟐
EN of H = 2.2
ΔEN = 0.0
2. 𝐂𝐇𝟒
EN of C = 2.55
EN of H = 2.2
ΔEN = 0.35
Electronegativity Difference
Bond Polarity
(DEN) range
ΔEN ≤ 0.4 Nonpolar covalent bond
1.7 > ΔEN > 0.4 Polar covalent bond
ΔEN ≥ 1.7 Ionic covalent bond
Valence Shell Electron Pair
Repulsion (VSEPR) theory
helps to predict the geometry
of individual molecule from
the number of paired
electrons around the central
atoms.
Examples of
Polar
molecule
Polar
molecule
𝐇𝟐 𝐎
-Bent shape
-polar due to
two lone pairs
Polar
molecule
Polar
molecule
𝐂𝐇𝟐 𝐎
-Trigonal planar
-polar due to two
lone pairs
Examples of
non-Polar
molecule
Non-polar
molecule
𝐂𝐎𝟐
- Linear
- nonpolar due to equal
distribution of polar
bonds
Non-polar
molecule
Oxygen is more
electronegative than
carbon. Therefore, the
C-O bonds are polar.
Non-polar
molecule
Since CO2 has a linear
symmetrical structure, the dipole
moments of the C-O bonds
cancel out.
- CO2 is a nonpolar molecule.
𝐂𝐂𝐥𝟒
- Tetrahedral
- nonpolar
due to equal
distribution of
polar bonds
Example 2: Sulfur dioxide (SO2) is a
colorless toxic gas formed by burning
sulfur in air.
1. Correct Lewis structure and
geometry
2. Oxygen is more electronegative
than sulfur. Therefore, the S—O
bonds are polar.
3. Since the molecule is bent-shaped,
the dipole moments do not cancel
out.
SO2 is a polar molecule.
STEPS TO DRAW LEWIS STRUCTURE
1. Count all the valence electrons
2. Determine the central atom
3. Draw single bonds to the central
atom
4. Put all remaining valence electrons
on atoms as lone pairs
5. Turn lone pairs into double / triple
bonds to give every atom an octet
(duet)
Generally, you can tell if a
molecule is polar or nonpolar
based on:
• its structure or shape
• the polarity of the
individual bonds
present in the
molecule
Try it!
• Ammonia (NH3)is a
colorless gas. A solution of
ammonia in water is used as
a cleaning agent. Determine
if ammonia is polar or
nonpolar.
Polar molecule
• NH3 - Trigonal pyramidal
- polar due to one lone pair
..
H N H
H
Key Points
•Polarity means having dipoles, a
positive and a negative end. Based
on polarity, molecules can be polar
or nonpolar.
•Polar molecules have dipoles. Their
dipole moments do not add up to
zero (or do not cancel out).
Key Points
•Nonpolar molecules do not have
positive or negative ends. Their dipole
moments add up to zero (they cancel
out).
•In general, you can tell if a molecule is
polar or nonpolar based on the shape of
the molecule and the polarity of the
individual bonds present in the
molecule.
seatwork: Determine the polarity of the
following compounds based on
electronegativity differences and molecular
geometry.
Molecular geometry Polarity
1. HBr linear polar
2. PH3
3. SiS2
4. O2
5. BCl3
seatwork
Bond Molecular Polarity of
Polarity Geometry Molecule
