Question

How does a molecules symmetry relate to polarity?

Answer 1

Polarity results from the vector sum of the individual bond dipoles. Clearly, molecular symmetry determines the vector sum

Explanation:

Take 2 molecules, `CF_4`, and `CHCl_3`. Both `C-Cl`, and `C-F` bonds are quite polar (the halogen is more electronegative than carbon, and the halogen atom polarizes electron density towards itself. Now, `F` is more effective than `Cl` in this activity. Nevertheless, `CF_4` is non-polar, whereas chloroform is quite polar as solvents go. Why?

Molecular polarity results from the vector sum of the individual bond dipoles. When the `CrarrF` dipoles are added, the overall vector sum is zero (necessarily, because `CF_4` is a regular tetrahedron. When the `CrarrCl` and the `C-H` dipoles are added, the resultant is non-zero.