The formation of self-assembled monolayers (SAMs) of omega-mercaploalkanoic acids on a mercury surface under potential control has been studied. Cyclic voltammetry and AC voltammetry were used for investigating the different phases and transitions that the homologous series of these thiols form and undergo. We find that the thiols are either physisorbed or chemisorbed depending on the applied potential and the transition between these two states occurs through a Faradaic process. Moreover, the chemisorption of the thiols results in multilayer deposition when the thiol monolayer does not block electron transfer. Finally, the implications of this study to the formation and manipulation of SAMs of omega-functionalized alkanethiols on Hg are discussed.