Octet Rule And Stability Of Atom

Most of the things we see in our everyday life are in a chemically combined state. Water is a combination of Hydrogen and Oxygen; common salt is a combination of sodium and chlorine and many more things like plastic, glass, etc. are made up of a combination of elements. So why do atoms combine? What do they gain by doing so? Let’s try to answer these questions.

The atoms combine to become stable by losing their energy. They do so by attaining their nearest noble gas configuration. Noble gas configuration refers to the electronic configuration of a noble gas. The unique feature of noble gases is that their outermost shell is filled.  Now the question arises, why the filled shell is the most stable or is in the least energy state. The reason is, in the case of completely filled orbitals, there’s more exchange of energy that leads to stability of an atom.

Octet Rule

What is Octet rule?

For the elements with atomic numbers between 3 and 20, 8 is the maximum no. of electrons that can be accommodated in the outermost shell. Hence, considering these elements, the general rule is that the elements are stable if it has 8 electrons in outermost orbit. The octet rule stating that atoms can combine either by transfer of valence electrons from one atom to another (gaining or losing) or by sharing of valence electrons to have an octet in their valence (or outermost) shells.

The rule was developed in 1916 by Kossel and Lewis and this theory of chemical combination is also known as the electronic theory of chemical bonding.

The following table shows the example for the octet rule

Element Electronic Configuration No. of e needed to complete octet configuration The preferred way of attaining stability
Sodium (11) 2,8,1 Lose 1 or gain 7 Prefers losing an eas it requires lesser energy than gaining 7.
Chlorine(17) 2,8,7 Lose 7 or gain 1 Prefers gaining an e as it requires lesser energy than losing 7.
Oxygen(16) 2,8,6 Lose 6 or gain 2 Prefers gaining 2 e as it requires lesser energy than losing 6.

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Practise This Question

SF6 and PCl5 are exceptions to octet rule because of _____.