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Chemical Bonding and Molecular Structure question

2019 · 10 Apr · Shift 1 · Q5
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  5. /2019 · 10 Apr · Shift 1 · Q5

Chemical Bonding and Molecular Structure question

2019 · 10 Apr · Shift 1 · Q5

JEE MainChemistryChemical Bonding and Molecular StructureMCQ+4 / −1
During the change of O2O_2O2​ to O2−O_2^-O2−​ , the incoming electron goes to the orbital :
  1. A
    π2py\pi 2{p_y}π2py​
  2. B
    σ∗2pz{\sigma ^*}2{p_z}σ∗2pz​
  3. C
    π∗2px{\pi ^*}2{p_x}π∗2px​
  4. D
    π2px\pi 2{p_x}π2px​
View written solutionFree

Correct answer: C

  1. Write the molecular orbital configuration of O2O_2O2​

For O2O_2O2​ (and F2F_2F2​), the order of valence molecular orbitals is:

σ2s<σ∗2s<σ2pz<π2px=π2py<π∗2px=π∗2py<σ∗2pz\sigma 2s < \sigma^*2s < \sigma 2p_z < \pi 2p_x = \pi 2p_y < \pi^* 2p_x = \pi^* 2p_y < \sigma^* 2p_zσ2s<σ∗2s<σ2pz​<π2px​=π2py​<π∗2px​=π∗2py​<σ∗2pz​

O2O_2O2​ has 121212 valence electrons. Filling these orbitals gives:

(σ2s)2(σ∗2s)2(σ2pz)2(π2px)2(π2py)2(π∗2px)1(π∗2py)1(\sigma 2s)^2(\sigma^*2s)^2(\sigma 2p_z)^2(\pi 2p_x)^2(\pi 2p_y)^2(\pi^* 2p_x)^1(\pi^* 2p_y)^1(σ2s)2(σ∗2s)2(σ2pz​)2(π2px​)2(π2py​)2(π∗2px​)1(π∗2py​)1
  1. Now form O2−O_2^-O2−​

O2−O_2^- O2−​ has one extra electron compared to O2O_2O2​.

So the incoming electron will occupy the next available lowest-energy molecular orbital.

In O2O_2O2​, the partially filled highest occupied orbitals are:

π∗2pxandπ∗2py\pi^* 2p_x \quad \text{and} \quad \pi^* 2p_yπ∗2px​andπ∗2py​

These two are degenerate, so the added electron enters one of the π∗2p\pi^* 2pπ∗2p orbitals.

  1. Match with the given options
  • A: π2py\pi 2p_yπ2py​ → already fully filled, not correct
  • B: σ∗2pz\sigma^*2p_zσ∗2pz​ → higher in energy, not correct
  • C: π∗2px\pi^* 2p_xπ∗2px​ → correct
  • D: π2px\pi 2p_xπ2px​ → already fully filled, not correct

Hence, the incoming electron goes to:

π∗2px\boxed{\pi^* 2p_x}π∗2px​​

Note: Because π∗2px\pi^* 2p_xπ∗2px​ and π∗2py\pi^* 2p_yπ∗2py​ are degenerate, either label could represent the orbital receiving the extra electron. Among the given options, only C matches this.

  1. Comparison with stored correct answer

Stored correct answer: C

Derived answer: C

So the derived answer agrees with the stored correct answer.

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