Question

The bond order of CO and NO is:
a.) 3 and 2
b.) 3 and 2.5
c.) 3 and 1.3
d.) 3 and 3.5

Answer 1

Hint: We should know that bond order is the number of bonded electron pairs between two atoms. We can find the bond order of the above atoms by the use of molecular orbital theory.

Complete step by step answer:
Let us understand the bond order by taking one example that is of di-nitrogen. In diatomic nitrogen (N≡N), for instance, the bond order is 3 because there are 3 chemical bonds linking the two nitrogen atoms. We can use molecular orbital theory, to find bond order. In molecular orbital theory, we define bond order as half of the difference between the number of bonding and antibonding electrons.
\[\mathbf{Bond}\text{ }\mathbf{order}\text{ }=\dfrac{\text{1}}{2}\left[ \left( \mathbf{Number}\text{ }\mathbf{of}\text{ }\mathbf{electrons}\text{ }\mathbf{in}\text{ }\mathbf{bonding}\text{ }\mathbf{molecules} \right)\text{ }-\text{ }\left( \mathbf{Number}\text{ }\mathbf{of}\text{ }\mathbf{electrons}\text{ }\mathbf{in}\text{ }\mathbf{antibonding}\text{ }\mathbf{molecules} \right) \right]\]

First we should write the molecular orbital electronic configuration of CO molecules. \[\]\[C-O:\,\,\sigma 1{{s}^{2}}{{\sigma }^{*}}1{{s}^{2}}\sigma 2{{s}^{2}}{{\sigma }^{*}}2{{s}^{2}}\pi 2{{P}_{x}}^{2}=\pi 2p_{y}^{2}\sigma 2P_{y}^{2}\]
\[Bond\,order=\dfrac{No.\,of\,bonding\,electrons(10)-No.\,of\,electrons\,inABMO(4)}{2}=3\]
So, from the above calculation the bond order of carbon monoxide molecules is 3.

Now, we will find the bond order of Nitric oxide by the same molecular orbital method.
So, first we will write the molecular orbital configuration of Nitric oxide.
\[N-O:~\sigma 1{{s}^{2}}{{\sigma }^{*}}1{{s}^{2}}\sigma 2{{s}^{2}}{{\sigma }^{*}}2{{s}^{2}}\pi 2P_{x}^{2}=\pi 2{{P}_{z}}^{2}\sigma 2{{P}_{z}}^{2}{{\pi }^{*}}2{{P}_{x}}^{1}\]
\[Bond\,order=\dfrac{No.\,of\,bonding\,electrons(10)-No.\,of\,electrons\,inABMO(5)}{2}=2.5\]
So, the bond order of a nitric oxide molecule is 2.5.
So, from the above discussion now we know that the bond order of carbon monoxide and nitric oxide molecules is 3 and 2.5 respectively.
So, the correct answer is “Option B”.

Note: We know about calculating bond order, now we should know the significance of knowing bond order. We should know that, if the molecule has higher bond order, that molecule will be more stable. We should answer this by molecular orbital theory; the electron that entered a bonding molecular orbital will help stabilize the new molecule. Each electron that entered an anti-bonding molecular orbital will act to destabilize the new molecule. We should note that if the bond order is zero, the molecule cannot form. The higher bond orders indicate greater stability for the new molecule.