Results from Monte Carlo (MC) simulations for restricted electrolytes are presented for both 1:1 and 2:1 electrolytes. It is shown that the potential drop across the diffuse layer for these systems may be expressed by a Taylors series in the Gouy-Chapman (CC) estimate of the same quantity. The coefficients of this series are defined in terms of the MSA volume fraction and the reciprocal thickness of the ionic atmosphere. The series model can also be used to estimate the differential capacity of the diffuse layer. The properties of unrestricted electrolytes are considered at or very close to the potential of zero charge. (C) 2009 Elsevier Ltd. All rights reserved.