We present a quantitative approach for the determination of the initial steps of a chemical reaction from only the properties of the isolated reagents. This approach is based on the empirical principle of hard and soft acids and bases and allows the calculation of the energy variation of the interacting system as a function of the number of electrons in each reactant. The application of this approach to the interaction of the Ga 2 As 2 molecule with Na and Cl atoms is presented, as well as the comparison of these results with calculations of first principles for the total energy of the interacting system.
