Illustrated Glossary of Organic Chemistry

Expanded octet (hypervalent): A valence shell electron count that exceeds eight electrons.


In methane (CH4), carbon has a full octet (eight valence electrons).


In phosphate ion (PO43-), each oxygen has a full octet (eight valence electrons), whereas phosphorus has an expanded octet (ten valence electrons).


In sulfuric acid (H2SO4), each oxygen has a full octet (eight valence electrons), whereas sulfur has an expanded octet (twelve valence electrons).