Why is BrCN a polar molecule?
- BrCN is a polar molecule because the electrons are not "pulled" with the "same strength" by the constituents. (not the exact chemistry explanation but just to help make it clear - see electronegativity).
Due to differences in electronegativity, there is an unequal sharing of the electrons therefore it is a polar molecule:
As you can see, the nonpolar molecules have equal "pull" of electrons whereas the polar molecules are the opposite.
For a great explanation: