A molecule may have a very strong dipole if it has a large difference in electronegativity between its constituent atoms. Electronegativity is the measure of an atom's ability to attract electrons. When two atoms with significantly different electronegativities bond, the more electronegative atom will attract the electrons more strongly, creating a partial negative charge on itself and a partial positive charge on the other atom. This separation of charge results in a strong molecular dipole.

For instance, consider the molecule hydrogen chloride (HCl). Chlorine is more electronegative than hydrogen, so the electrons in the covalent bond are pulled more towards the chlorine atom. This creates a partial negative charge on the chlorine atom and a partial positive charge on the hydrogen atom. The resulting molecular dipole is quite strong, giving HCl a polar character.

Another example is the water molecule (H2O). Oxygen is more electronegative than hydrogen, so the electrons in the O-H bonds are pulled more towards the oxygen atom. This creates a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. The arrangement of these partial charges results in a bent molecular structure and a strong molecular dipole, making water a polar molecule.

The strength of the molecular dipole can influence various properties of the molecule, such as its solubility, boiling point, and reactivity. Molecules with strong dipoles tend to be more soluble in polar solvents and have higher boiling points due to stronger intermolecular forces. Additionally, the presence of a strong molecular dipole can affect the molecule's chemical reactivity, as it can influence the attraction or repulsion between the molecule and other molecules or ions.