The aggregation of neutral organic molecules on electrode surfaces to form oligomers or surface micelles and the phase transformations of an adsorbed monolayer were studied by means of statistical mechanics. The model developed for aggregation phenomena predicts that the formation of oligomers is not depicted in the capacitance plots, which exhibit the same features as those for adsorption of monomers under all circumstances. The equilibrium between monomers and oligomers extends throughout the polarization range where these two states of the adsorbate coexist. As the number of monomer units in the aggregates increases, monomers and aggregates tend to separate, occupying different polarization regions. In addition, the equilibrium between monomers and large aggregates leads in general to complicated capacitance plots characterized by the appearance of very sharp capacitance peaks. The same features characterize the formation of mixed two-dimensional micellar films on electrode surfaces. Phase transformations of adsorbed monolayers on electrode surfaces, which may lead to the formation of either two immiscible concentrated surface solutions of adsorbate in solvent and vice versa or pure adsorbate precipitate, are examined within the framework of the molecular models developed in this series of papers. The separation of the adsorbed layer to immiscible surface solutions is related to the short-range particle-particle interactions, whereas the surface precipitation process is considered as an aggregation process where the aggregation number tends to infinity. It is shown that in general there is an acceptable agreement between theory and experiment.