194.
Briefly explain the term 'Dipole moment'. How is it expressed and what are its units?
Dipole moment :When a covalent bond is formed between atoms of different elements, the bonded pair is attracted more towards the atom of higher electronegativity. Thus, the molecule acquires polarity with a partial negative charge (δ–) on the most electronegative atom and a partial positive charge (δ+) on the less electronegative atom. As the ends of the molecule are having different .charges, they are also called dipoles. For example,
Hδ+ - Clδ–.
The polarity of a molecule is expressed in terms of dipole moment. It is the product of the magnitude of the charge on either end of the dipole and the distance separating the charges. If e is the magnitude of the charge and d is the distance separating the charges, then
μ = e X d
where μ represents the dipole moment.
Dipole moment is a measure of the polarity of the covalent bond. It is expressed by an arrow pointing from positive pole to the negative pole with a small tail at the positive charge (→).
Unit of dipole moment. Since the charge is of the order of 10–10 e.s.u. and distance is of the order of 10–8 cm, the value of the dipole moment is of the order of 10–10 - 10–8 e.s.u. cm or 10–18 e.s.u. cm = 1
Debye or 1 D.
∴ μ = 10–18 e.s.u. cm = i D
Thus, units of dipole moment are debye (D).
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