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1. Molecular Polarity
AP Chemistry

2. Polar vs. Non-Polar Molecules
Polarity in a molecules determines
whether or not electrons in that
molecule are shared equally.
When determining the polarity of a
molecule, it is all about symmetry.
Asymmetric molecules tend to be polar.
Symmetric molecules are always non-
polar.

3. When determining the polarity of a
molecule, follow these steps:
Draw the Electron Dot structure of the
molecule.
Using the electronegativity chart determine
the difference in electronegativity for each
bond.
0—0.4 = Non-polar
0.5—1.7 = Polar

4. The molecule is non-polar if :
each bond in the molecule is non-polar
and there are no
unbonded electron pairs.
each bond in the molecule has the same
polarity and there
are no unbonded electron pairs on
the central atom.
There is no net dipole moment (all
moments cancel out)

5. The molecule is polar if:
There is a net dipole moment
each bond in the molecule is non-polar,
but there are unbonded electron pairs on
the central atom.
bonds in the molecule have different
polarities and/or there
are unbonded electron pairs on the
central atom.

6. Dipole Moments
Dipole Moments (μ) - a quantitative
measure of the polarity of a bond.
μ = charge x distance = Q x r
(distance is in meters)
Dipole moment units are the Debye
Bond dipole moment is a vector quantity –
it has a magnitude and direction.
Molecular dipole moment = vector sum of
all bond moments

7. Dipole Moment
Direction of the polar bond in a molecule.
Arrow points toward the more e-neg atom.
H Cl
+ -

8. Nonpolar Molecules
Dipole moments are symmetrical and
cancel out.
BF3
F
F F
B

9. Polar Molecules
–Dipole moments are asymmetrical and
don’t cancel .
–Molecule has a net dipole moment.
net
dipole
moment
H2O
H H
O

10. Determining Molecular Polarity
Depends on:
–dipole moments
–molecular shape

11. Polar Bonds vs. Polar Molecules
The effect of polar bonds on the
polarity of the entire molecule depends
on the molecule shape
–carbon dioxide has two polar bonds, and
is linear = nonpolar molecule!

12. Polar molecules
The effect of polar bonds on the
polarity of the entire molecule depends
on the molecule shape
– water has two polar bonds and a bent shape;
the highly electronegative oxygen pulls the e-
away from H = very polar!

13. CHCl3
H
Cl Cl
Cl
Determining Molecular Polarity
Therefore, polar molecules have...
– asymmetrical shape (lone pairs) or
– asymmetrical atoms
net
dipole
moment