Question

How do dipoles cancel out?

Answer 1

Electric dipoles are vector quantities, so like forces, two or more of them can add up to zero.

Explanation:

Consider a case like the `CO_2` molecule. This is linear in shape with the carbon atom located between the two oxygen atoms.

Both of the C=O double bonds are polar, but as they are "equal and opposite" (to make the analogy to forces), the dipoles cancel, or add to a total of zero, if you prefer to think of it that way.

As the image shows, this results in a molecule that is negative at each end and positive in the middle. The charge separation that we associate with dipoles does exist, but this molecule is not polar because it does not have one end negative and the opposite end positive in charge .

This situation frequently occurs in more complex 3-dimensional molecules that show a high degree of symmetry in their shape, such as the tetrahedral structure of `CH_4` which is such a common building block of organic molecules.