Question

Among the following allotropic forms of sulphur, the number of allotropic forms, which will show paramagnetism is ______.

• A. $\mathrm{\alpha }-\mathrm{sulphur}$
• B. $\mathrm{\beta }-\mathrm{sulphur}$
• C. ${\mathrm{S}}_2-\mathrm{form}$

Answer 1

The correct option is C

${\mathrm{S}}_2-\mathrm{form}$

Explanation for correct option:

(C) ${\mathbf{S}}_{\mathbf{2}}\mathbf{-}\mathbf{form}$

1. In vapor phase sulphur exists as ${\mathrm{S}}_2$ molecule.
2. ${\mathrm{S}}_2$ has two unpaired electrons in anti-bonding $3\mathrm{p}$ - orbital thus, it shows paramagnetic behaviour.

Electronic configuration of ${\mathrm{S}}_2$ : $\left({\mathrm{\sigma }}^{2}3\mathrm{s}\right)\left({{\sigma }^{*}}^{\mathit{2}}3s\right)\left({\sigma }^{\mathit{2}}3p_z\right)\left({\pi }^{\mathit{2}}3p_{x,y}\right)\left({\pi }^{\mathit{2}}3p_{x\mathit{,}y}\right)\left({\pi }^{\mathit{*}\mathit{1}}3p_{x,y}\right)\left({\pi }^{\mathit{*}\mathit{1}}3p_{\mathit{x}\mathit{,}\mathit{y}}\right)$

No. of unpaired electrons $=2$

Bond Order $$\begin{gathered} =\left(8-4\right)/2 \\ =2 \end{gathered}$$

Explanation of incorrect options:

(A) $\mathbf{\alpha }\mathbf{-}\mathbf{sulphur}$

$\mathrm{\alpha }-\mathrm{sulphur}$ do not have unpaired electrons thus, it does not show paramagnetic behavior.

(B) $\mathbf{\beta }\mathbf{-}\mathbf{sulphur}$

$\mathrm{\beta }-\mathrm{sulphur}$ do not have unpaired electrons thus, it does not show paramagnetic behavior.

Hence option C is correct, ${\mathrm{S}}_2-\mathrm{form}$ will show paramagnetism.