Dipole Moment

In a heteronuclear molecule, the shared pair of electrons is more towards the more electronegative element leading to the development of a partial negative charge on the more electronegative atom. The development of partial charge is due to the proximity of a shared pair of electrons towards an atom and this is known as the polarity of bonds. The strength of the polarity of bonds can be measured in terms of dipole moment. An electric dipole is a pair of two objects having equal and opposite charges, separated by a distance.

Dipole Moment

What is Dipole Moment?

A dipole moment is the product of the magnitude of the charge and the distance between the centers of positive and negative charges. It is denoted by the Greek letter ‘µ’.

Mathematically,

Dipole Moment (µ) = Charge (Q) * distance of separation (r)

It is measured in Debye units denoted by ‘D’.
1 D = 3.33564 × 10-30 Cm
Where C is Coulomb and m is in meters.

General facts about Dipole Moment: 

  1. The dipole moment of a single bond in a polyatomic molecule is known as bond dipole and it is different from the dipole moment of the molecule as a whole.
  2. It is a vector quantity i.e. it has magnitude as well as definite directions.
  3. Being a vector quantity, it can also be zero as the two oppositely acting bond dipoles can cancel each other.
  4. By convention, it is denoted by a small arrow with tail on negative center and head on positive center. But in chemistry, the dipole moment is represented by a slight variation of the arrow symbol.
    It is denoted by a cross on positive center and arrowhead on negative center. This arrow symbolizes the shift of electron density in the molecule.
  5. In the case of a polyatomic molecule, the dipole moment of the molecule is the vector sum of the all present bond dipoles in the molecule.

Calculating dipole moment – BeF2

Dipole Moment

In the case of Beryllium and Fluorine, F is more electronegative than Be, hence the electron density will shift more towards F.  Since BeF2 is a planar molecule and the angle between two bonds is 180o. The two bond dipoles which are equal in magnitude but opposite in direction cancel each other out. This leads to resultant zero dipole moment of BeF2.

Magnetic Dipole Moment

Magnetic Dipole Moment is a measure of the magnetic strength of a current carrying coil or a magnet, expressed as the torque per unit magnetic-flux density produced when the coil or magnet is set with its axis perpendicular to the magnetic field m, j also known as the magnetic moment.


Practise This Question

According to Newlands’ Law of Octaves, the properties of lithium and sodium were found to be same because sodium is the eighth element after lithium.