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.
Source: