Definition - What does Octet Rule mean?
The octet rule states that atoms gain or lose electrons to attain an outer shell electron configuration nearest that of a noble gas. The attractive force between atoms is informally measured with this rule.
The octet rule dictates particular electron placement on the orbitals of the atom's nucleus. It also determines whether electrons are added or lost through chemical reactions, and measures chemical reactivity of atoms based upon their specific electron configuration.
Corrosionpedia explains Octet Rule
The octet rule describes how elements generally prefer to form bonds so that they can attain eight electrons in their valence shell to become noble gases. Noble gases have outer shells with electrons occupying all available spaces. Bonding behavior and reactivity of elements can be predicted by applying this rule. All elements other than noble gases have a deficiency or surplus of electrons in their valence shell, causing a positive or negative charge. Atoms of elements tend to react in such a way so that it achieves the electronic configuration of noble gases.
While this rule generally applies for metals and nonmetals, it is not of much use in dealing with compounds of the transition elements in which d or f orbitals are involved in bonding. Plus, this rule doesn't accurately predict the electron configurations of all molecules and compounds. Consequently, this rule has to be used with care in predicting the electron configurations.
Atoms that accommodate the octet rule have greater stability and emit less energy.