Q. Which of the following ions has the least magnetic moment?
AMUAMU 2007
Solution:
Ion
Electronic configuration
No. of unpaired electrons
$Cu^{2+}$
$d^9$
$1$
$Ni^{2+}$
$d^8$
$2$
$Co^{2+}$
$d^7$
$3$
$Fe^{2+}$
$d^6$
$4$
Magnetic moment $(\mu)=\sqrt{n(n+2)} BM$
Here $n=$ number of unpaired electrons.
(a) Magnetic moment of $Cu ^{2+}$,
$\mu =\sqrt{1(1+2)} BM$
$=1.73 \,BM$
(b) Magnetic moment of $Ni ^{2+}$,
$\mu =\sqrt{2(2+2)} BM $
$=2.84\, BM$
(c) Magnetic moment of $Co ^{2+}$,
$\mu =\sqrt{3(3+2)} BM$
$=3.86 \,BM$
(d) Magnetic moment of $Fe ^{2+}$,
$\mu =\sqrt{4(4+2)} BM $
$=4.90 \,BM$
Hence, $Cu ^{2+}$ has only one unpaired electron.
Therefore, $Cu ^{2+}$ has least magnetic moment.
| Ion | Electronic configuration | No. of unpaired electrons |
|---|---|---|
| $Cu^{2+}$ | $d^9$ | $1$ |
| $Ni^{2+}$ | $d^8$ | $2$ |
| $Co^{2+}$ | $d^7$ | $3$ |
| $Fe^{2+}$ | $d^6$ | $4$ |