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NEET CHEMISTRYMedium

Four diatomic species are listed below. Identify the correct order in which the bond order is increasing in them.

A

O2<NO<C22<He2+O_{2}^{-} < NO < C_{2}^{2-} < He_{2}^{+}

B

C22<He2+<O2<NOC_{2}^{2-} < He_{2}^{+} < O_{2}^{-} < NO

C

He2+<O2<NO<C22He_{2}^{+} < O_{2}^{-} < NO < C_{2}^{2-}

D

NO<O2<C22<He2+NO < O_{2}^{-} < C_{2}^{2-} < He_{2}^{+}

Step-by-Step Solution

To determine the increasing order of bond order, we apply the principles of Molecular Orbital Theory (MOT) to calculate the bond order (B.O.) for each species using the formula: B.O.=12(NbNa)B.O. = \frac{1}{2}(N_{b} - N_{a}), where NbN_{b} is the number of bonding electrons and NaN_{a} is the number of antibonding electrons .

  1. He2+He_{2}^{+}: This species has 3 electrons. The configuration is (σ1s)2(σ1s)1(\sigma 1s)^{2} (\sigma^{*} 1s)^{1} . Bond Order = 12(21)=0.5\frac{1}{2}(2 - 1) = 0.5.
  2. O2O_{2}^{-} (Superoxide ion): This species has 17 electrons. Starting from the O2O_{2} configuration (16 electrons, B.O. = 2.0), the additional electron occupies an antibonding π\pi^{*} orbital . Bond Order = 12(107)=1.5\frac{1}{2}(10 - 7) = 1.5 .
  3. NONO (Nitric oxide): This species has 15 electrons. The configuration includes 10 bonding electrons and 5 antibonding electrons (with one electron in a π\pi^{*} orbital). Bond Order = 12(105)=2.5\frac{1}{2}(10 - 5) = 2.5.
  4. C22C_{2}^{2-}: This species has 14 electrons and is isoelectronic with N2N_{2} . The configuration is (σ1s)2(σ1s)2(σ2s)2(σ2s)2(π2px2=π2py2)(σ2pz)2(\sigma 1s)^{2} (\sigma^{*} 1s)^{2} (\sigma 2s)^{2} (\sigma^{*} 2s)^{2} (\pi 2p_{x}^{2} = \pi 2p_{y}^{2}) (\sigma 2p_{z})^{2} . Bond Order = 12(104)=3.0\frac{1}{2}(10 - 4) = 3.0 .

Comparing the values: He2+(0.5)<O2(1.5)<NO(2.5)<C22(3.0)He_{2}^{+} (0.5) < O_{2}^{-} (1.5) < NO (2.5) < C_{2}^{2-} (3.0). Thus, the correct increasing order is given in Option 3.

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