# How can I identify dipoles in molecules?

Jun 4, 2015

You look for electronegativity differences between the atoms that are bonded to each other.

A bond dipole depends on electronegativity differences (Δ"EN") between the atoms in the bond.

This causes the electrons in the bond to spend more time around one atom than the other.

For example, in $\text{HCl}$, the $\text{Cl}$ is more electronegative than $\text{H}$, so the electrons spend more time around $\text{Cl}$ than $\text{H}$.

We indicate a bond dipole by an arrow with a "+" at one end and pointing towards the negative end of the bond.

If Δ"EN" < 0.5, we usually say that the bond is ionic.

EXAMPLE

Identify the bond dipoles on chloromethane, $\text{CH"_3"C} l$.

Solution

The structure of chloromethane is

Δ"EN" for the $\text{C-H}$ bond is 0.4. The $\text{C-H}$ bond is nonpolar.

Δ"EN" for the $\text{C-Cl}$ bond is 0.6. The $\text{C-Cl}$ bond is polar.

The $\text{Cl}$ atom is the negative end of the bond, so there is a $\text{C-Cl}$ bond dipole.