Expanded Octet

A hypervalent molecule (the phenomenon is sometimes colloquially known as expanded octet) is a molecule that contains one or more main group elements formally bearing more than eight electrons in their valence shells. Phosphorus pentachloride (PCl5), sulfur hexafluoride (SF6), chlorine trifluoride (ClF3), and the triiodide (I3−) ion are examples of hypervalent molecules.

Read more about Expanded Octet:  Definitions and Nomenclature, History and Controversy, Criticism, Bonding in Hypervalent Molecules

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