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

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

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

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