1. Molecular Polarity Notes
Which Molecules Have Dipole Moments?
Any two atom molecule (diatomic) with a polar bond.
With three or more atoms (polyatomic) there are two considerations.
There must be a polar bond. (H2O & NH3)
Geometry can’t cancel it out.

2. Dipole Moments
A molecule with a center of negative charge and a center of positive charge is dipolar (two poles), or has a dipole moment.
Center of charge doesn’t have to be on an atom.
Will line up in the presence of an electric field.

3. When no electric field is present, the molecules are randomly oriented
When no electric field is present, the molecules are randomly oriented. When the field is turned on, the molecules tend to line up with their negative ends toward the positive pole and their positive ends toward the negative pole.

4. C. Bond Polarity and Dipole Moments
A dipole moment results when a polar molecule has a center for positive charge separate from a center for negative charge

5. How It is drawn
H - F d+ d-
The dipolar character of a molecule is often represented by an arrow pointing to the negative charge center with the tail of the arrow indicating the positive center of charge

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

7. B. Determining Molecular Polarity
Depends on:
dipole moments
molecular shape

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

9. B. Determining Molecular Polarity
Polar Molecules
Dipole moments are asymmetrical and don’t cancel .
H2O H O
net
dipole
moment

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

11. C. Bond Polarity and Dipole Moments
Water molecule dipole moment

12. C. Bond Polarity and Dipole Moments
The polarity of water affects its properties
Permits ionic compounds to dissolve in it
Causes water to remain liquid at higher temperature

13. Some Molecules Have Polar Bonds, but Do Not Have Dipole Moment.
This occurs when the individual bond polariteis are arranged in such a way that they cancel each other out.
EX: CO2 molecule (oppose bond polarities cancel out)

14. Geometry and polarity Three shapes will cancel them out.
Planar triangles
120º

15. Geometry and polarity
Three shapes will cancel them out.
Tetrahedral

16. Geometry and polarity
Others don’t cancel
Bent

17. Geometry and polarity
Others don’t cancel
Trigonal Pyramidal