dipole
A dipole occurs when two opposite charges are separated by some amount of distance. We have already seen dipoles in the form of polar bonds. For example, each O-H bond in water is an example of a dipole; the partial positive charge on hydrogen is separated from the partial negative charge on oxygen by the length of the bond. A molecular dipole is the geometric sum of all the individual bond dipoles in a molecule. In order for a molecule to have a dipole, it must have at least one polar bond. However, not all molecules with polar bonds have an overall molecular dipole. Sometimes the dipoles within a molecule will effectively cancel each other out, giving a zero net molecular dipole. This is often seen in symmetrical molecules.