The Frumkin interaction parameter between aromatic molecules (neutral form) adsorbed from aqueous solution on mercury electrode, is related to the balance of energy dispersion terms (adsorbate-adsorbate) and water-water molecular interaction reflecting the role played by substitution on the electrode surface of water by the aromatic molecule. The interaction among adsorbed aromatics (in neutral form) is always attractive, so that the sign of a(F) (Frumkin parameter, positive or negative) arises from that kind of balance. For aromatic anions, taking into account a large partial charge transfer from the adsorbate to the metal surface, the change of Delta G(ADS)(0) at varying the coverage (theta) is mainly due to electrostatic repulsion among charge adsorbed particles.