What determines the polarity of a molecule?

1 Answer
Feb 20, 2017

Answer:

The vector sum of the individual bond dipoles.

Explanation:

Possibly the indication of this is the relative polarity of #"chloroform"#, #CHCl_3#, versus #"carbon tetrachloride"#, #"CCl"_4#. Both molecules have #""^(+delta)C-Cl^(delta-)# bonds, which are reasonably polar.

If we sum up the individual bond dipoles, however, #"CCl"_4# sums TO ZERO, and thus has ZERO DIPOLE MOMENT - if you don't see this consider vector addition with very symmetrical tetrahedral bond angles. Because the #1xx""^(-delta)C-H^(delta+)# and #3xx""^(+delta)C-Cl^(delta-)# bond dipoles in chloroform do not sum to ZERO, the molecule has a resultant dipole moment. #""^(+delta)H-Cl^(delta-)#, and #""^(-delta)OH_2^(delta+)# are polar molecules by this same reasoning.