question_answer

Which of the following has \[{{p}_{\pi }}-{{d}_{\pi }}\] bonding? [AIPMT 2002]

A) \[NO_{3}^{-}\]

B) \[SO_{3}^{2-}\]

C) \[BO_{3}^{3-}\]

D) \[CO_{3}^{2-}\]

Correct Answer: A

Solution :

[a] In \[SO_{3}^{2-}\]  the S is \[s{{p}^{3}}\] hybridised, so

\[\underset{\begin{smallmatrix}  \text{(Sulphur atom in} \\  \text{   excited state)} \end{smallmatrix}}{\mathop{_{16}S=1{{s}^{2}},\,2{{s}^{2}}\,2{{p}^{6}}}}\,,\,\underbrace{3{{s}^{2}}3p_{x}^{1}3p_{y}^{1}3p_{z}^{1}}_{s{{p}^{3}}\,\text{hybridisation}}\,\underset{\text{unhybridised}}{\mathop{3d_{xy}^{1}}}\,\]

In \['S'\] the three p-orbitals forms \[\sigma \] bonds with three oxygen atoms and unhybridised d-orbital is involved in \[\pi \] bond formation

\[_{16}O=\,1{{s}^{2}},2\,{{s}^{2}}\,2p_{x}^{2}\,2p_{y}^{1}\,2p_{z}^{1}\]

In oxygen two unpaired p-orbitals are present, one is involved in \[\sigma \] bond formation while other is used in \[\pi \] bond formation.

Thus in \[SO_{3}^{2-}\] \[{{p}_{\pi }}\] and \[{{d}_{\pi }}\] orbitals are involved for \[{{p}_{\pi }}-{{d}_{\pi }}\] bonding.