Polarity in a molecule is observed when the molecule exhibits partial charges.

This is actually how water in a glass is all together instead of separating itself into little single molecules of water. The oxygen of one water molecule is attracted to the positive hydrogens of another water molecule.

The more electonegative the atom, the more polar the molecule. However, the position of the electronegative atoms can cause the charge to be cancelled out (as in carbon tetrachloride).

I just liked all these words, and felt like playing around with them.