Question

Which of the following species have identical bond order?

• A.
• B.
• C.
• D. None of the above

Answer 1

Answer: (B), (C)

The correct options are
B

C

To determine the bond order, first we have to see the MO energy diagrams of all the molecules

We know that whenever there is a '-' sign on a molecule, we have to add an extra electron and whenever there is a '+' sign on a molecule, we have to remove an electron.

Therefore,

$N_2$ $\to$14 electrons

${N_2}^{+}$$\to$13 electrons (1 less electron)

${N_2}^{-}$ $\to$15 electrons (1 more electron)

Now, lets take a look at the bond order.

Bond Order = $\frac{1}{2}$[Bonding electrons - Anti bonding electrons]

$N_2$ $\Rightarrow$ BO = $\frac{1}{2}$[10 - 4]=3

${N_2}^{+}$ $\Rightarrow$ BO = $\frac{1}{2}$[9 - 4]=2$\frac{1}{2}$

${N_2}^{-}$ $\Rightarrow$ BO = $\frac{1}{2}$[10 - 5]=2$\frac{1}{2}$

Therefore, we can see that bond order of ${N_2}^{+}$ and ${N_2}^{-}$ is same.