Effective atomic number of a metal in a complex is defined as the total number of electrons possessed by the metal including those donated by the ligands. EAN = Z – X + 2n. Where, Z is atomic number of metal, X is oxidation number of metal in the complex and n is the number of ligands. In general, EAN of a metal in a complex = number of electrons in nearest inert gas element. However, in some cases EAN can be few units above or below the number of electrons in inert gas element.
