Term: hypervalency
https://doi.org/10.1351/goldbook.HT07054

Definition:
The ability of an atom in a molecular entity to expand its valence shell beyond the limits of the Lewis octet rule. Hypervalent compounds are common for the second and subsequent row elements in groups 15–18 of the periodic table. A description of the hypervalent bonding implies a transfer of the electrons from the central (hypervalent) atom to the nonbonding molecular orbitals which it forms with (usually more electronegative) ligands. A typical example of the hypervalent bond is a linear three-centre, four-electron bond, e.g. that of Fap–P–Fap fragment of PF5.

Related Terms:
1) valence (http://doi.org/10.1351/goldbook.V06588).
2) lewis octet rule (http://doi.org/10.1351/goldbook.LT07065).
3) ligands (http://doi.org/10.1351/goldbook.L03518).

Source: PAC, 1999, 71, 1919. 'Glossary of terms used in theoretical organic chemistry' on page 1946 (https://doi.org/10.1351/pac199971101919)

Citation: 'hypervalency' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.HT07054

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