The ECW model created by Russell S. Drago is a quantitative model that describes and predicts the strength of Lewis acid base interactions, . The model assigned  and  parameters to many Lewis acids and bases. Each acid is characterized by an  and a . Each base is likewise characterized by its own  and . The  and  parameters refer, respectively, to the electrostatic and covalent contributions to the strength of the bonds that the acid and base will form. The equation is
The  term represents a constant energy contribution for acid–base reaction such as the cleavage of a dimeric acid or base. The equation predicts reversal of acids and base strengths. The graphical presentations of the equation show that there is no single order of Lewis base strengths or Lewis acid strengths.