The octet rule states that atoms bond to share or gain electrons to achieve a noble gas electron configuration with 8 electrons in their outer shell, which provides stability. Atoms follow this rule to achieve the most stable electron configuration possible. The octet rule works best for elements with low atomic weights up to 20 but does have some limitations, as some elements can be stable without achieving an octet or by expanding their octet.

1. The Octet Rule

2. •The octet rule in chemistry is the principle that
bonded atoms share their eight outer electrons.
(A pair of electrons that is shared between two
atoms is called a bond pair.
•A pair of electrons that is not shared between
two atoms is called a lone pair.)
•This gives the atom a valence shell resembling
that of a noble gas. They have completed outer
electron shells, which make them very stable.

3. Why Elements Follows the Octet Rule?
Atoms follow the octet rule because they always
seek the most stable electron configuration.
Following the octet rule results in completely
filled s- and p- orbitals in an atom's outermost
energy level. Low atomic weight elements (the
first 20 elements) are most likely to adhere to the
octet rule.

4. A Lewis electron dot diagram may be drawn to
illustrate the octet rule.

6. Limitations of Octet Rule :
(1) Hydrogen with 1 electron attains stability by sharing,
gaining or losing 1 valence electron. It does not need to
complete octet to attain stability. Also, He has only 2
electrons and is stable.
(2) Incomplete octet: In certain molecules such as BeH2,
BeCl2, BH3, BF3, the central atom has less than 8 electrons in
its valence shell, yet the molecule is stable.
(3) Expanded octet: In certain molecules such as PF5, SF6,
IF7, H2SO4, the central atom has more than 8 valence
electrons, yet the molecule is stable.