Molecules with central atoms seemingly exceeding eight electrons, often better described by three-center bonding.
Practise Bonding & Molecular Structure All Bonding & Molecular Structure topics
Hypervalency refers to molecules in which a main-group central atom appears to have more than eight valence electrons, as in SF6 or PF5. Classical explanations invoked expansion of the valence shell through d orbitals, but computational studies indicate that d orbitals contribute little to bonding in these molecules. Modern descriptions use ionic contributions and three-center four-electron bonds, in which four electrons are shared over three atoms in a linear arrangement. Hypervalent molecules are typically formed with highly electronegative ligands such as fluorine. The term describes the electron count rather than a specific bonding mechanism.
Key ideas: Recognize by counting electrons: more than 8 around a main-group atom in the Lewis structure (SF6 has 12, ClF3 has 10, XeF2 has 10). Bonding pictures: three-center four-electron bond (F-S-F with 4 electrons over 3 centres) and strong ionic resonance forms. Use formal charge to see the alternative: in sulfate, formal charges are reduced but real S-O bonds are polar single bonds with ionic character.
Common mistakes and connections: Typical mistakes are to claim d orbital hybridization as fact, or to say second row elements can be hypervalent (they cannot: no PF5 analogue with N). Also, fluorine and oxygen ligands favour hypervalency while hydrogen and carbon do less so. Links to expanded octet, three-center bonds, VSEPR and sp3d labels.
Chlorine in ClF3 appears to have ten valence electrons, three bonds and two lone pairs, though bonding is explained more by polar three-centre ideas. The interactive lesson shows this as a live animation or chart.
SF6 and PF5 are hypervalent, with twelve and ten electrons respectively around the central atom.
Molecules with central atoms seemingly exceeding eight electrons, often better described by three-center bonding.
Hypervalency is a advanced topic in Bonding & Molecular Structure. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in Bonding & Molecular Structure first: Color of Transition Metal Complexes, Isomerism in Complexes, Hydrogen Molecule Ion.
The next topics in Bonding & Molecular Structure are Three-Center Two-Electron Bond and Banana Bonds.
Yes. The interactive lesson includes a self-check question on Hypervalency, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Hypervalency is topic 98 of 104 in Bonding & Molecular Structure.