SCH 3U
Molecular Polarity
Name: __________________
Applying shapes & ENDs
Recall : a polar bond has a positive end and a negative end due to unequal sharing of electrons between two atoms.
e.g. H – O
**Oxygen has a higher EN therefore it hogs electrons. The O end of the bond is more negative.
Polar molecules contain overall unequal sharing of electrons (not specific to one bond).
These molecules end up with one end (or side) that is more negative, and one more positive end.
In order to be a polar molecule, two criteria must be met:
1. There must be at least one polar bond
2. The bond polarities must not ‘cancel out’.
To cancel out, the polarities must be equal in strength (same  ENs) and opposite in direction.
To represent a polar molecule, and to show where it’s negative end / positive end are, we use a large arrow pointing
towards the negative end.
Is the molecule polar or non-polar? To determine this;
a) Show the electron tally for each molecule. Draw the Lewis Structure.
b) Show the structural formula, and name the shape of each compound.
c) Calculate the E.N.D. for each bond, add δ −and δ + symbols onto the structures if necessary.
d) Indicate with an arrow any net dipole in the molecule and then state whether each molecule is polar or non-polar.
Cl2
CCl4
PCl3
The following shapes will allow dipoles to cancel out (if they are equal in strength):
 tetrahedral
 trigonal planar (planar triangular)
 linear
Ranking Molecules by Increasing Polarity (First complete the polarity practice worksheet then answer this question)
In each of the following problems, rank the molecules from lowest to highest polarity:
1. PF3, SF2, NF3
____________________________________________
2. B2F4, H2C2O4, CF2O
____________________________________________
3. PH3, PF3, NH3, NF3
____________________________________________
4. H2O, HF, H2
____________________________________________
Polarity Practice
For each of the following pairs of compound, determine which is most polar. This is determined by;
drawing both the Lewis structure and structural formula for each compound and using VSEPR to
determine the overall polarization of the molecule. Circle the chemical formula of the compound that is
more polar.
Be sure to include the following;
a) Show the electron tally for each molecule. Draw the Lewis Structure.
b) Show the structural formula, and name the shape of each compound.
c) Calculate the E.N.D. for each bond, add δ −and δ + symbols onto the structures if necessary.
d) Indicate with an arrow any net dipole in the molecule and then state whether each molecule is polar or non-polar.
1. methyl chloride (CHCl3)
or
methyl bromide (CHBr3)
2. hydrogen sulfide _________
or
water __________
3. hydrochloric acid __________
or
hydroiodic acid __________
4. silicon tetrabromide __________
or
hydrogen cyanide _________
5.sulfur difluoride __________
or
carbon disulfide __________
6. nitrogen trifluoride __________
or
oxygen dichloride__________
7. boron trihydride __________
or
ammonia __________