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I was just reading about how Nitrogen and Oxygen combine to form Nitric oxide. Image result for n2 + o2 = 2no
My question is, why would this reaction even occur? Isn't the valency of Nitrogen 3- and Oxygen 2-, and therefore this reaction seems to form a product that still hasn't achieved the octet electronic configuration.
Could I please have some help? Thank you in advance.

Edit: Or even $\ce{N2O}$ or $\ce{NO2}$ for that matter?

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  • $\begingroup$ NO is one of most common stable radicals. $\endgroup$
    – Mithoron
    Mar 2, 2015 at 14:02
  • $\begingroup$ Btw, welcome to the community of chemistry.SE! This might be interesting. $\endgroup$
    – M.A.R.
    Mar 2, 2015 at 14:10
  • $\begingroup$ @MARamezani So the octet rule does not always hold? I assume that should be in really rare cases. $\endgroup$
    – SR1
    Mar 3, 2015 at 16:07
  • $\begingroup$ @ShashankRammoorthy Actually yes. Octet isn't something microscopic world has to always follow. They've got their own criminals you know! :) Wikipedia takes short notes on the exceptions, but I think it covers all of them. Or, you could google something like "octet exceptions", or, a better way is to search chemistry.SE! $\endgroup$
    – M.A.R.
    Mar 3, 2015 at 16:29

2 Answers 2

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You're right: $\ce{NO}$ is a free radical and the reaction between $\ce{N2}$ and $\ce{O2}$ can be achieved - supposed that enough energy is provided.

This may happen through an electrical arc discharge in the lab or, in the mesosphere (50-85km above earth) through ionizing cosmic rays. Note however that nitric oxide react with oxygen to eventually furnish nitrogen dioxide $\ce{2 NO + O2 <=> 2 NO2}$.

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Think about it this way. If a molecule of nitrogen and a molecule of oxygen were to collide with enough kinetic energy to break the bonds that hold the molecules together, and they collide at such an angle that allows their orbitals to overlap and form new bonds, then $\ce{NO}$ can be made. The octet rule is a rule. Whenever you see the word rule in chemistry you should think that it can be broken, some rules are broken often.

The reaction is endothermic and is not spontaneous but by random chance, some $\ce{NO}$ can form in a mixture of nitrogen and oxygen.

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  • $\begingroup$ So NO should be unstable, right? Nitrogen's valency is not satisfied. $\endgroup$
    – SR1
    Mar 3, 2015 at 16:02

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