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

2. When determining the polarity of a molecule, follow these steps:
Draw the Electron Dot structure of the molecule.
Determine the VSEPR geometry
Decide if the the molecule is symmetric or not.
this is by looking at the VSEPR geometry
polarity (dipole moments) within the individual bonds

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

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

6. 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.

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

8. 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!

9. Molecular Dipole Moments
Carbon dioxide has no dipole moment
The bonds are polar covalent
VSEPR shape is linear
because individual bond dipoles cancel each other out.
They are equal and opposite 18

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

11. 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!

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

13. Figure 1.13
Carbon tetrachloride
Dichloromethane 20

14. Figure 1.13
Resultant of these two bond dipoles is
Resultant of these two bond dipoles is
Carbon tetrachloride has no dipole moment because all of the individual bond dipoles cancel. 20

15. Figure 1.13
Resultant of these two bond dipoles is
Resultant of these two bond dipoles is
The individual bond dipoles do not cancel in dichloromethane; it has a dipole moment. 20