Matter Trends and Chemical Bonding
3.3
Polar Bonds and Molecules
Learning Goals
• By the end of this class I will…
– Determine if a molecule is polar or non-polar
– Identify polar and non-polar molecules
Last Class
• Identified electronegativity
• Determined the trend for electronegativity
• Determined how to calculate ΔEN and use this
information to decide if a bond is
– Ionic: ΔEN > 1.7
– Polar covalent: 0 < ΔEN < 1.7
– Non-polar covalent: ΔEN = 0
Electronegativity
• Recall:
– Electronegativity is the measure of an atom’s
ability to attract electrons within a bond
– Electronegativity decreases down a group,
increases across a period
– Can predict the type of bond based on ΔEN
Covalent
0
Non-polar
Increasing polarity
Ionic
1.7
Polar Covalent Bonds
• Recall:
– A polar bond is a covalent bond between atoms
which have a significant ΔEN
– The electron pair (bonding electrons) are not
shared evenly.
– Electrons are found closer to the more EN atom
– Unequal distribution of electrons causes the
atoms to have partial charges (δ+, δ-)
– The more EN atom has a δ- charge
Polar Covalent Bonds
Let’s take a look at some polar bonds
[OH]HCl
Polar Molecules
• A molecule that contains polar bonds AND is
asymmetrical in terms of charge
Examples: H2O, NCl3
Question: Is CH4 a polar molecule?
Non-polar because it is symmetrical!
Polar Molecules
Steps to determine if a molecule is polar
1. Determine if polar bonds are present
2. Determine if the molecule is asymmetrical
(may need lewis structure/model kit)
If 1 and 2 are true,
the molecule is polar!
Polar Molecules
Determine if the following molecules are polar
or non-polar
1. CHCl3
2. CO2
3. C2H5OH
Exit Ticket
Determine if the following molecules are polar
or non-polar
1. NH3
2. CCl4
Homework
Page 107
Practice #1
(may want to
use model kits)
Page 108
#1 and 5