Expanded Octet
A bonding arrangement in which a central atom is surrounded by more than eight valence electrons.
Unit
Dimensionless
In depth
Only elements of period 3 and beyond can do this, because they are large enough to accommodate extra bonded atoms and have accessible d orbitals. The resulting hypervalent species adopt trigonal bipyramidal, octahedral or pentagonal bipyramidal geometries and are common among the heavier p-block elements.
Examples in the real world
PCl₅ with ten electrons, SF₆ with twelve, and IF₇ with fourteen around the central atom.