Using Dipole moments to determine if a molecule is polar or non polar

[Blanca Cervantes]

Problem 2E.29 asks which of the three isomers of dichlorobenzene, C6H4Cl2, are polar. Can anyone explain to me how they went about solving this problem? How do you determine which isomer is polar?

[asannajust_1J]

I drew all three isomers. and since Cl is the most electronegative, it has the negative dipole in the 1,4 structure it is nonpolar since the dipoles are directly across from each other (so they cancel), but in isomer 1,3 and 1,2 the dipoles do not cancel thus they are polar.

[Adam Kramer 1A]

You need to draw the dipoles with the shape to see how they would cancel. If every area of electron density is filled with an atom of equal electronegativity, there is probably no dipole since all the pull is the same and would cancel; if there is a missing atom and lone pairs instead, or a different atom with different electronegativity, there is probably a net dipole since the pull is not equal in every direction.