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Chemical Bonding and Molecular Structure question

2023 · 29 Jan · Shift 2 · Q5
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  5. /2023 · 29 Jan · Shift 2 · Q5

Chemical Bonding and Molecular Structure question

2023 · 29 Jan · Shift 2 · Q5

JEE MainChemistryChemical Bonding and Molecular StructureMCQ+4 / −1
According to MO theory the bond orders for O22−\mathrm{O}_2^{2 - }O22−​, CO\mathrm{CO}CO and NO+\mathrm{NO^+}NO+ respectively, are
  1. A
    1, 3 and 3
  2. B
    2, 3 and 3
  3. C
    1, 2 and 3
  4. D
    1, 3 and 2
View written solutionFree

Correct answer: A

  1. Use bond order formula

According to MO theory,

Bond order=Nb−Na2\text{Bond order} = \frac{N_b - N_a}{2}Bond order=2Nb​−Na​​

where NbN_bNb​ = number of electrons in bonding MOs and NaN_aNa​ = number of electrons in antibonding MOs.


  1. For O22−\mathrm{O}_2^{2-}O22−​

First, O2\mathrm{O}_2O2​ has 16 electrons, so O22−\mathrm{O}_2^{2-}O22−​ has 18 electrons.

For oxygen and beyond, the MO filling order is:

σ(2s), σ∗(2s), σ(2pz), π(2px)=π(2py), π∗(2px)=π∗(2py)\sigma(2s),\ \sigma^*(2s),\ \sigma(2p_z),\ \pi(2p_x)=\pi(2p_y),\ \pi^*(2p_x)=\pi^*(2p_y)σ(2s), σ∗(2s), σ(2pz​), π(2px​)=π(2py​), π∗(2px​)=π∗(2py​)

In O2\mathrm{O}_2O2​, bond order is 2. Adding two more electrons to form O22−\mathrm{O}_2^{2-}O22−​ fills the two π∗\pi^*π∗ antibonding orbitals.

So bond order decreases by 1:

B.O. of O22−=1\text{B.O. of } \mathrm{O}_2^{2-} = 1B.O. of O22−​=1
  1. For CO\mathrm{CO}CO

Carbon has 6 electrons and oxygen has 8 electrons, so total electrons:

6+8=146 + 8 = 146+8=14

CO\mathrm{CO}CO is isoelectronic with N2\mathrm{N}_2N2​ (14 electrons).

For 14-electron species like N2\mathrm{N}_2N2​ and CO\mathrm{CO}CO, bond order is:

333

So,

B.O. of CO=3\text{B.O. of } \mathrm{CO} = 3B.O. of CO=3
  1. For NO+\mathrm{NO}^+NO+

Nitrogen has 7 electrons, oxygen has 8 electrons, and the positive charge means one electron is removed:

7+8−1=147 + 8 - 1 = 147+8−1=14

So NO+\mathrm{NO}^+NO+ is also isoelectronic with N2\mathrm{N}_2N2​ and CO\mathrm{CO}CO.

Hence,

B.O. of NO+=3\text{B.O. of } \mathrm{NO}^+ = 3B.O. of NO+=3
  1. Final sequence

Thus, the bond orders for O22−\mathrm{O}_2^{2-}O22−​, CO\mathrm{CO}CO and NO+\mathrm{NO}^+NO+ respectively are:

1, 3, 31,\ 3,\ 31, 3, 3

So the correct option is:

A: 1,31, 31,3 and 333


  1. Comparison with stored answer

Stored correct answer = A.

Our derived answer = A.

So they agree.

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