Why do atoms tend to acquire noble gas configurations ?

W. Kossel and G.N.Lewis (1916) observed that during chemical reactions, atoms of all elements tend to achieve noble gas configurations. Based on this observation, they proposed a theory for the formation of chemical bonds. According to this theory,

“During any chemical reaction, the atoms of all the elements tend to gain stability by acquiring an electronic configuration of the nearest noble gas element.”

Thus, during chemical reactions atoms of all elements tend to achieve eight electrons in their outermost shell. This is known as the octet rule.

Hydrogen atom, however gains stability by either losing its only electron, or by gaining one to have two electrons (helium structure) in its outermost shell, viz.

H → H⁺ + e^–

H + e^– → H^–

Thus, all atoms tend to acquire noble gas configuration to gain stability.

The octet rule is found useful for describing bonding in a large number of cases. There are some examples where the octet rule is not found applicable. For example, in compounds like phosphorus pentachloride (PCl₅) and sulphur hexafluoride (SF₆) there are more than 8 electrons around the central atom as shown alongside.