Thiols of short alkyl chain length and different terminal group charge (COO- and NH3+), and covalently attached ferrocene via terminal NH2 and ferrocene carboxyaldehyde were self assembled on gold electrodes. Electron transfer to Fe(CN)(6)(3-) in solution and to covalently attached ferrocene centres were studied at different pH by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Changes in solution pH result in variation of the self assembled monolayer (SAM) terminal group charge. The disparate heterogeneous electron transfer apparent rates obtained from R-ct have been described on the basis of the Boltzmann surface concentration factor and the potential distribution model of Smith and White and that of Fawcett for the Au-SAM-electrolyte interface.