The octet rule states that atoms tend to gain, lose, or share electrons to achieve eight electrons in their valence shell, resembling a noble-gas electron configuration. It is a useful bonding model, but several stable species do not obey it.
How the Octet Rule Works
In covalent compounds, atoms share electron pairs. Each bonding pair counts as two electrons around each bonded atom, while lone pairs also contribute to the valence-shell total.
For example, in , carbon forms four single covalent bonds, so it has eight electrons around it. Each chlorine has one bonding pair and three lone pairs, also giving it an octet.
Hydrogen is an exception to the number eight because its first energy level can hold only two electrons. It therefore follows a duet rule, as in .
