Question

What are the limitations of the octet rule?

Answer 1

Hint : We know that the octet rule is not universal although it is useful. It is quite useful for understanding the structural arrangement of most organic compounds and mainly applies to the elements of the second period of the periodic table. There are three exceptions of octet rule

Complete Step By Step Answer:
In scientific history we have seen multiple attempts of solving the mystery of how atoms bond with each other. In $1904$ , we saw a significant move forward when Richard Abegg proposed the concept of coordination number. This concept is considered as an extension to the concept of valency (the combining power of an element). He proposed that atoms can behave as either donor or acceptors of electrons. The octet rule uses this idea as a basis and states that every atom binds with another atom in order to have eight electrons in its outermost shell by donating or accepting electrons. Significance of Octet Rule this rule is able successfully explain the formation of various compounds and explain the stability of the compound.
The octet rule states that atoms can combine either by transferring or by sharing their valence electrons to attain an octet of electrons in their valence shell.
One limitation of the octet rule is that it cannot be applied to the nonmetals after silicon in the Periodic Table.
These elements can “expand their octet” and have more than eight valence electrons around the central atom.

Additional Information:
The octet rule is not satisfied for all atoms in molecules with an odd number of electrons such as nitric oxide, $NO$ and nitrogen dioxide, $N{{O}_{2}}.$ In addition to the $3s$ and $3p$ orbitals, elements in and beyond the third period of the periodic table also have $3d$ orbitals available for bonding. There are more than eight valence electrons around the central atom in a number of compounds of those elements. This is called the expanded octet. Obviously, in such cases the Octet rule does not apply.

Note :
Remember that in the solution given above, we have seen multiple examples of compounds that follow or do not follow octet rule. A common theme in all those compounds was that all of the atoms there after bonding had even numbers of electrons surrounding them. But we also have compounds in which some atoms have an odd number of electrons in their outermost shell.