Chemical hardness is one of the chemical reactivity descriptors of chemical species and this concept has widely benefited from the development of Density Functional Theory (DFT). In the present report, chemical hardness values for approximately fifty diatomic molecules have been calculated using a new molecular hardness (eta(M)) equation derived by us in recent times. Then, correlation between force constant (k) and chemical hardness for the above mentioned diatomic molecules that situate hydrides, halides, oxides and sulfides among them has been investigated. Consequently, a relation that can be presented by a simple equation between chemical hardness with bond stretching force constants has,been found. (C) 2015 Elsevier B.V. All rights reserved.