# How does a molecules symmetry relate to polarity?

Nov 23, 2015

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

#### Explanation:

Take 2 molecules, $C {F}_{4}$, and $C H C {l}_{3}$. Both $C - C l$, 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 $C l$ in this activity. Nevertheless, $C {F}_{4}$ 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 $C \rightarrow F$ dipoles are added, the overall vector sum is zero (necessarily, because $C {F}_{4}$ is a regular tetrahedron. When the $C \rightarrow C l$ and the $C - H$ dipoles are added, the resultant is non-zero.