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AIIMS 2016
Exam
AIIMS
Year
2016
Subject
Chemistry
Chapter
Chemical Bonding and Molecular Structure

AIIMS 2016 · Chemistry · Chemical Bonding and Molecular Structure

Four diatomic species are listed below in different sequences....

Four diatomic species are listed below in different sequences. Which of these represents the correct order of their increasing bond order?

Options

  1. AC22−<He2+<NO<O2−\mathrm{C}_2^{2-} < \mathrm{He}_2^{+} < \mathrm{NO} < \mathrm{O}_2^{-}
  2. BHe2+<O2−<NO<C22−\mathrm{He}_2^{+} < \mathrm{O}_2^{-} < \mathrm{NO} < \mathrm{C}_2^{2-}
  3. CO2−<NO<C22−<He2+\mathrm{O}_2^{-} < \mathrm{NO} < \mathrm{C}_2^{2-} < \mathrm{He}_2^{+}
  4. DNO<C22−<O2−<He2+\mathrm{NO} < \mathrm{C}_2^{2-} < \mathrm{O}_2^{-} < \mathrm{He}_2^{+}

Correct answer

B. He2+<O2−<NO<C22−\mathrm{He}_2^{+} < \mathrm{O}_2^{-} < \mathrm{NO} < \mathrm{C}_2^{2-}

Step-by-step solution

According to molecular orbital theory, the energy level of the given molecules are C22−→σ1s2σ⋆1s2σ2s2σ⋆2s2π2px2π2py2σ2pz2 B.O. =1/2[10−4]=3He2+→σ1s2σ⋆1s1 B.O. =1/2[2−1]=1/2=0.5NO→σ1s2σ⋆1s2σ2s2σ⋆2s2σ2pz2π2px2π2py2π⋆2px1\begin{aligned} & \mathrm{C}_2^{2-} \rightarrow \sigma 1 s^2 \sigma^{\star} 1 s^2 \sigma 2 s^2 \sigma^{\star} 2 s^2 \pi 2 p_x^2 \pi 2 p_y^2 \sigma 2 p_z^2 \\ & \text{ B.O. }=1 / 2[10-4]=3 \\ & \mathrm{He}_2^{+} \rightarrow \sigma 1 s^2 \sigma^{\star} 1 s^1 \\ & \text{ B.O. }=1 / 2[2-1]=1 / 2=0.5 \\ & \mathrm{NO} \rightarrow \sigma 1 s^2 \sigma^{\star} 1 s^2 \sigma 2 s^2 \sigma^{\star} 2 s^2 \sigma 2 p_z^2 \pi 2 p_x^2 \pi 2 p_y^2 \\ & \quad \pi^{\star} 2 p_x^1\end{aligned} B.O. =1/2[10−5]=2.5O2−→σ1s2σ⋆1s2σ2s2σ⋆2s2σ2pz2π2px2π2py2π⋆2px2 B.O. =1/2[10−7]=1.5π⋆2py1\begin{aligned} & \text{ B.O. }=1 / 2[10-5]=2.5 \\ & \mathrm{O}_2^{-} \rightarrow \sigma 1 s^2 \sigma^{\star} 1 s^2 \sigma 2 s^2 \sigma^{\star} 2 s^2 \sigma 2 p_z^2 \pi 2 p_x^2 \pi 2 p_y^2 \pi^{\star} 2 p_x^2 \\ & \text{ B.O. }=1 / 2[10-7]=1.5 \\ & \pi^{\star} 2 p_y^1 \\ & \end{aligned}So,thecorrectorderoftheirincreasingbondorderisSo, the correct order of their increasing bond order is\mathrm{He}_2^{+} < \mathrm{O}_2^{-} < \mathrm{NO} < \mathrm{C}_2^{2-}$
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