Q. Which one of the following shows highest magnetic moment ?
Solution:
The paramagnetism or magnetic moment produced due to spin of electrons or unpaired cloctrons is expressed in terms of Bohr magneton $(BM)$ or $\mu_{B}$ and given by
Magnetic moment $(\mu)=\sqrt{[n(n+2)]} BM$
where $n$ is the number of unpaired electrons, in species. Thus, greater is the number of unpaired electrons in an ion greater is its paramagnetic nature.
Ion
Electronic configuration
No. of unpaired $e^-$ s
$Cr ^{3+}$
$d^{3}$
3
$Fe ^{2+}$
$d^{6}$
4
$Co ^{2+}$
$d^{7}$
3
$Ni ^{2+}$
$d^{8}$
2
As $Fe ^{2+}$ ion has maximum number of unpaired electrons, thus it has highest magnetic moment.
| Ion | Electronic configuration | No. of unpaired $e^-$ s |
|---|---|---|
| $Cr ^{3+}$ | $d^{3}$ | 3 |
| $Fe ^{2+}$ | $d^{6}$ | 4 |
| $Co ^{2+}$ | $d^{7}$ | 3 |
| $Ni ^{2+}$ | $d^{8}$ | 2 |