JEE Main & Advanced Chemistry Chemical Bonding and Molecular Structure / रासायनिक आबंधन एवं आणविक संरचना Dipole moment

         ?The product of magnitude of negative or positive charge (q) and the distance (d) between the centres of positive and negative charges is called dipole moment?.           

\[\mu =Electric\text{ }charge\times bond\text{ }length\]

As q is in the order of \[{{10}^{-10}}\] esu and d is in the order of \[{{10}^{-8}}\] cm, m is in the order of \[{{10}^{-18}}\] esu cm. Dipole moment is measured in "Debye" (D) unit. \[1D={{10}^{-18}}\] esu cm = \[3.33\times {{10}^{-30}}\] coulomb metre (In S.I. unit).           

Dipole moment is indicated by an arrow having a symbol  pointing towards the negative end. Dipole moment has both magnitude and direction and therefore it is a vector quantity.           

Symmetrical polyatomic molecules are not polar so they do not have any value of dipole moment.         

Unsymmetrical polyatomic molecules always have net value of dipole moment, thus such molecules are polar in nature. H2O, CH3Cl, NH3, etc are polar molecules as they have some positive values of dipole moments.    

\[\mu =0\]due to unsymmetry             

(1) Dipole moment is an important factor in determining the geometry of molecules. Molecular geometry and dipole moment

General formula	Molecular geometry	Dipole moment	Example
AX	Linear	May be non zero	HF, HCl
	Linear Bent or V-shape	Zero Non zero
	Triangular planar Pyramidal T-shape	Zero Non zero Non zero
	Tetrahedral Square planar See saw	Zero Zero Non zero
	Trigonal bipyramidal Square pyramidal	Zero Non zero
	Octahedral Distorted octahedral	Zero Non zero
	Pentagonal bipyramidal	Zero

(2) Every ionic compound having some percentage of covalent character according to Fajan's rule. The percentage of ionic character in compound having some covalent character can be calculated by the following equation.           

The % ionic character                   .            

(3) The trans isomer usually possesses either zero dipole moment or very low value in comparison to cis?form