Question

In an exam, I have been asked about the number of lone pairs in the molecule NO, the answer has been given as 2. According to Wikipedia, there is a structure relating a three electron bond as a third bond, but doesn't it violate the octet of oxygen?

I kind of understand that the octet rule is old and has been disproven, I haven't found any explanation for this phenomenon, the only other fact that supports it (which I have found) is the bond order from MOT, but I don't understand it.

Answer 1

Nitrogen monoxide (NO) is an exception to the octet rule as it has an odd number of electrons with a total of one lone pair and one unpaired electron on nitrogen, as elucidated by Molecular Orbital Theory.

Step-by-step explanation:

The molecule nitrogen monoxide (NO) indeed does not follow the conventional octet rule due to an odd number of valence electrons present in its structure. Considering the valence electrons, nitrogen brings five and oxygen brings six to the molecule, resulting in a total of eleven valence electrons.

Using Molecular Orbital Theory (MOT), the eleventh electron in NO is placed in a degenerate pi* orbital, resulting in a bond order of 2 1/2. The presence of fewer than eight electrons around the nitrogen is compensated by the partial double-bond character indicated by MOT, which also aligns with the observed properties of the NO molecule such as its bond length and bond energy.