Discuss the magnetic properties of transition elements.

In presence of magnetic field, two types of magnetic behaviour is observed for transition elements $(i)$ Paramagnetism $(ii)$ Diamagnetism. Paramagnetic substances are attracted by magnetic field while diamagnetic substances are repelled by the magnetic field.

Ferromagnetism is extreme form of para-magnetism where substance is very strongly attracted by the magnetic field. The para-magnetism arises from the presence of unpaired electrons in $(n-1) d-$ orbitals each such electron having a magnetic moment associated with its spin as well as orbital motion. For most of the transition elements, the orbital contribution is not of much significance.

The magnetic moment expresses the para-magnetic behaviour of transition metal ions and is calculated by using "Spin-only" formula $\mu=\sqrt{n(n+2)}$ $BM$ where,

$n=$ number of unpaired electrons in $(n-1) d$-orbitals

$\mu=$ Magnetic moment in Bohr Magneton ($BM$)

Ion	Configuration	Unpaired electron $(s)$	calculated Magnetic moment	observed Magnetic moment
$\mathrm{Sc}^{3+}$	$3 d^{0}$	$0$	$0$	$0$
$\mathrm{Ti}^{3+}$	$3 d^{1}$	$1$	$1.73$	$1.75$
$\mathrm{Tl}^{2+}$	$3 d^{2}$	$2$	$2.84$	$2.76$
$\mathrm{V}^{2+}$	$3 d^{3}$	$3$	$3.87$	$3.86$
$\mathrm{Cr}^{2+}$	$3 d^{4}$	$4$	$4.90$	$4.80$
$\mathrm{Mn}^{2}$	$3 d^{5}$	$5$	$5.92$	$5.96$
$\mathrm{Fe}^{2+}$	$3 d^{6}$	$4$	$4.90$	$5.3-5.5$
$\mathrm{Co}^{2+}$	$3 d^{7}$	$3$	$3.87$	$4.4-5.2$
$\mathrm{Ni}^{2+}$	$3 d^{8}$	$2$	$2.84$	$2.9-3.4$
$\mathrm{Cu}^{2+}$	$3 d^{9}$	$1$	$1.73$	$1.8-2.2$
$\mathrm{Zn}^{2+}$	$3 d^{10}$	$0$	$0$	$-$

The magnetic moment increases with the increase in number of unpaired electrons. If the magnetic moment is zero, the substance is diamagnetic and is repelled by magnetic field.