Octet Rule
Definition and meaning of Octet Rule in chemistry.
The octet rule is the principle that atoms tend to gain, lose, or share electrons to achieve 8 valence electrons (or 2 for hydrogen), matching the stable electron configuration of a noble gas.
In more detail
This guideline helps predict how atoms will bond together. Atoms with few valence electrons tend to lose them, while those with many tend to gain them or form covalent bonds. The rule explains the formation of many ionic and covalent compounds among main group elements. However, the octet rule is a guideline, not an absolute law; transition metals and some main group elements can exceed or fall short of the octet requirement through expanded octets or other bonding arrangements.
Key facts
| Field | General Chemistry |
|---|---|
| Duet rule | Hydrogen and helium need only 2 electrons instead of 8 |
| Basis | Noble gases like neon (Ne) and argon (Ar) are stable with 8 valence electrons |
| Common exceptions | Transition metals and expanded octets in compounds like PCl5 and SF6 |
In a water molecule (H2O), the oxygen atom forms two covalent bonds with hydrogen atoms, giving oxygen 8 valence electrons around it and each hydrogen 2 valence electrons, both satisfying the rule.
Frequently asked questions
Why do atoms follow the octet rule?
Noble gases with 8 valence electrons are extremely stable and unreactive. Atoms achieve stability by adopting a noble gas electron configuration through bonding.
Are there exceptions to the octet rule?
Yes. Hydrogen needs only 2 electrons; transition metals often exceed 8; and some main group elements in the third period and beyond form expanded octets.