Octet Rule
The observation that atoms tend to gain, lose or share electrons until they are surrounded by eight valence electrons.
Unit
Dimensionless
In depth
The rule reflects the special stability of a filled ns² np⁶ configuration and successfully predicts the formulae of most main-group compounds. Hydrogen, lithium and beryllium follow a duplet instead, boron is often content with six, and period 3 onwards can expand beyond eight using low-lying d orbitals.
Examples in the real world
Chlorine gains one electron to reach an octet in Cl⁻; carbon shares four pairs to reach eight in CH₄.