As we know a polar molecule contain partial positive and partial negative poles. The ability of a polar molecule to become oriented in electrical field is called “Dipole moment”.
Mathematically dipole moment is the product of charge of the pole and the distance between two poles as;
Dipole moment = charge of pole x Distance between pole
μ = e x d
The S.I Unit of dipole moment is debye (columb x m)
1 Debye = 3.335x 10-30 col.m
1 Debye = 10-18 esu. Cm
Generally the value of dipole moment is in the order of 10-30 coul. m. This is between the change of pole is generally in order of 10-18 coul while the distance between poles is in order of 10-10 m.
Dipole moment depends upon:
i. Polarity of molecule.
ii. Geometrical structure of molecule.
Polarity of Molecule:
Dipole moment depends upon polarity of molecule. Greater the magnitude of the charge of pole greater will be dipole movement of atoms. This is due to the electronegativity of atoms. For example the dipole movement of HF is greater as compared to HCL because the electronegativity of ‘F’ is greater than ‘CL’.
In the case of non polar molecules dipole movement is zero due to absence of –ve and +ve poles.
Geometrical structure of Molecule:
Since dipole movement is a vector quality, therefore it is also possible that some molecules have polarity but their dipole movement is zero. This is mainly due to the linear structure of the molecule.
For example: the dipole movement of CO2 and CS2 is zero due to their Linear structures.