It is shown that the standard electrode potentials of the elements are a periodic property of the atomic number. The experimentally measured standard electrode potential of an element is related to fundamental elemental properties through a thermodynamic cycle. Metal atoms are first atomized to the vapor phase, are then ionized to form gaseous ions, and are then hydrated to form an ion-water cluster, which is next introduced into the aqueous solution. The standard electrode potential calculated from such a cycle is in good agreement with standard values for univalent, divalent and trivalent metal ions. It is shown that the periodicity in the standard electrode potential as a function of atomic number arises from the periodicity in the enthalpy term which is used to calculate standard electrode potentials from the equivalent thermodynamic cycle. (C) 2007 Published by Elsevier Ltd.