Expanded octet

Expanded octet is a colloquial term referring to the phenomenon of hypervalency where a central atom of a molecule bears more than eight electrons. Second-period atoms cannot have more than eight valence electrons around the central atom, but atoms in the third (and below) period can. In such a case, the atom is said to have an expanded octet. One example is SF6, where all six of sulfur's valence electrons form bonds with fluorine. Other examples are AsF5, & XeF6.