To entrust a Lewis period symbol to elements not having an octet of electron in your compounds.

You are watching: Which compound is an exception to the octet rule?

Three cases can be created that perform not follow the octet rule, and also as such, lock are well-known as the exceptions to the octet rule. Adhering to the Octet dominance for Lewis Dot structures leads come the most accurate depictions of steady molecular and atomic structures and also because the this we always want to use the octet dominance when illustration Lewis period Structures. However, the is hard to imagine that one rule could be complied with by all molecules. There is always an exception, and also in this case, three exceptions:

when there are an odd number of valence electrons once there space too few valence electrons when there space too plenty of valence electrons

Exception 1: species with Odd numbers of Electrons

The very first exception come the Octet dominion is once there are an odd number of valence electrons. An instance of this would be Nitrogen (II) Oxide also called nitric oxide ((ceNO). Nitrogen has actually 5 valence electrons while Oxygen has actually 6. The full would it is in 11 valence electrons to be used. The Octet preeminence for this molecule is fulfilled in the above example, yet that is through 10 valence electrons. The last one go not know where to go. The lone electron is dubbed an unpaired electron. But where must the unpaired electron go? The unpaired electron is usually put in the Lewis Dot structure so the each aspect in the framework will have actually the lowest formal fee possible. The formal fee is the perceived charge ~ above an individual atom in a molecule when atoms do not contribute equal number of electron to the binding they get involved in.

No formal charge at every is the most ideal situation. An instance of a secure molecule v an odd number of valence electrons would be nitric oxide. Nitric oxide has 11 valence electrons. If friend need an ext information around formal charges, view Lewis Structures. If us were to imagine nitric oxide had ten valence electron we would certainly come up v the Lewis structure (Figure (PageIndex1)):

Figure (PageIndex1): This is if nitric oxide has actually only ten valence electrons, which the does not.

Let"s look at the official charges of figure (PageIndex2) based on this Lewis structure. Nitrogen typically has five valence electrons. In figure (PageIndex1), it has actually two lone pair electrons and also it participates in two bonds (a double bond) through oxygen. This outcomes in nitrogen having a formal charge of +1. Oxygen typically has six valence electrons. In figure (PageIndex1), oxygen has four lone pair electrons and also it participates in 2 bonds with nitrogen. Oxygen as such has a formal charge of 0. The overall molecule here has a formal charge of +1 (+1 for nitrogen, 0 because that oxygen. +1 + 0 = +1).

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However, if we add the eleventh electron to nitrogen (because we desire the molecule to have the lowest complete formal charge), the will carry both the nitrogen and the molecule"s in its entirety charges to zero, the many ideal formal fee situation. That is specifically what is done to obtain the correct Lewis structure for nitric oxide (Figure (PageIndex2)):