In this paper we relate the change of chemical hardness and potential with the binding energies as the chemical binding takes place. We use a simple model to demonstrate that the hardness change is not only related to the binding energy of the molecule being formed, but also to the binding energies of the corresponding molecular cations and anions. Similar expressions are also derived for chemical potential. We have shown that our analysis can explain the existing data. The separated limit values of hardness and chemical potential are also derived. Two demonstrative calculations on the molecules H-2 and HF are presented. The future potential of this model is discussed.