1. Polar Molecules H F
electron rich
region
electron poor
region d+ d-

2. Dipole moment (µ)? A measure of molecular polarity m = q x r
A polar molecule has µ ≠ 0
Non-polar molecule has µ = 0
m = q x r
q = charge (coulomb)
r = the distance between charges (m)

3. The direction of polarity of a polar bond can be symbolised by a vector quantity
( )
The crossed end of the arrow is the positive end and the arrow head is the negative end.
H  Cl

4. Example:

5. Covalent bond between same atoms
Covalent bond between atoms of the same
element is nonpolar
→ nonpolar molecule.
Bonding electrons are shared equally.
Example:

6. Covalent bond between different atoms
is polar.
- bonding electrons closer to the more
electronegative atom.
However, molecules could be polar or
nonpolar, depending on its shape.

7. Determining polar and nonpolar molecules
Use the three-step approach outlined below :
Use electronegativity values to predict bond
dipoles.
Use the VSEPR method to predict the molecular shape.
From the molecular shape, determine whether bond dipoles cancel to give a non-polar molecule or combine to produce a (resultant dipole moment) for the molecule.

8. Molecules with different atoms & asymmetrically arranged are polar.
Example:

9. Molecules with different atoms, symmetrically
arranged but having µ = 0 are nonpolar.
Example:
In CCl4, each bond is polar.
The molecule as a whole, however, is nonpolar

10. Example:
In SF6, each bond is polar.
The molecule is nonpolar

11. Molecules with different atoms, symmetrically
arranged but having µ ≠ 0 are polar.
Example:
The molecule is polar because µ ≠ 0 .
The dipole moment arises because the difference
in electronegativity.

12. Cl C H H H Chloromethane ( CH3Cl) Example:
The molecule is polar because µ ≠ 0 .
The dipole moment arises because the difference
in electronegativity.

13. Molecules with lone pairs on the central atom
Let us consider the molecules in which there are lone pairs on the central atoms.
Note: Molecules which have lone
pairs are usually polar.

14. Ammonia ( effect of lone pairs )
Example: 
  0

16. Which of the following molecules have a dipole
moment?
H2O, CO2, SO2, and CH4 S O O H H
dipole moment
polar molecule
dipole moment
polar molecule C H C O
no dipole moment
nonpolar molecule
no dipole moment
nonpolar molecule

17. Exercise 1
Indicate the direction in which the shared electron pair is shifted in the molecules given
below.

18. Answer:

19. Exercise 2
Predicting the polarity of molecules.
State which of them are polar and which are nonpolar.
a) H2O
b) NH3
c) CCl4
d) CHCl3

20. Answer: