Question

Explain giving reasons:

Transition metals and many of their compounds show paramagnetic behaviour.

Answer 1

Paramagnetism in substances arises from the presence of unpaired electrons. Diamagnetic substances are those in which all the electrons are paired. Transition metal ions exhibit both diamagnetism and paramagnetism, i.e., two opposite effects, so the calculated magnetic moment is considered their resultant. Except for d⁰ (Sc³⁺, Ti⁴⁺) or d¹⁰ (Cu⁺, Zn²⁺) configurations, all simple ions of transition metals have unpaired electrons in their (n – 1)d subshells; hence, they are mostly paramagnetic. The magnetic moment of such an unpaired electron is related to spin angular momentum and orbital angular momentum. In compounds of metals of the first transition series, the contribution of orbital angular momentum is effectively quenched; hence, it is of no significance.

Therefore, the magnetic moment for them is determined on the basis of the number of unpaired electrons present in it, and it is calculated by the following ‘spin only’ formula.

μ = `sqrt (n(n + 2))`

Here, n is the number of unpaired electrons, and II is the magnetic moment, whose unit is the Bohr magneton (BM). Hence, the magnetic moment of an unpaired electron is 1.73 BM.