When a covalent bond is formed between two dissimilar atoms or we can say, heteronuclear molecules like HF, the electron pair shared between two atoms displaced towards the more electronegative atom(fluorine) since electronegativity of fluorine is far greater than that of hydrogen. The resultant covalent bond is a polar covalent bond. This is called polarisation.

As a result of polarization, the molecule acquires the dipole moment which can be defined as the product of the magnitude of the charge and the distance between the centers of positive and negative charge.

Dipole moment (u) = Charge (Q) × distance of separation (r)

Significances/Applications:

⇒The SI unit of Dipole moment is Debye. [ 1Debye = 3.35 × 10^-30m]

⇒Dipole moment is a vector quantity. It has a magnitude and a direction.

⇒It is represented by an arrow with tail on a negative charge and head pointing towards the positive charge. []

⇒It is measure of the polarity of a bond. For example, in HF molecule, the dipole moment for the H⁺F^- when an electron is completely transferred from hydrogen atom to fluorine atom is given by 4.48D.

⇒The dipole moment also used to calculate the per cent ionic character.

Per cent ionic character = × 100

⇒On the basis of dipole moment, we can also find out the structure of molecule