Question

Explain giving reason:

Transition metals and many of their compounds show paramagnetic behaviour.

Answer 1

Paramagnetism in substances originates due to the presence of unpaired electrons. Diamagnetic substances are those in which all the electrons are paired. Transition metal ions have both diamagnetism and paramagnetism, i.e., two opposite effects are found in them, so the calculated magnetic moment is considered to be their resultant magnetic moment. 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.