The elongating and shrinking of the interatomic distance creates harmonic potentials (Fig. ), and therefore many people considers a chemical bond in a stable geometry by considering not the force (F in eq. 1), but the force constant (f in eq. 2) of the hypothetical spring between the atoms, i.e. the second derivative of the potential energy as a function of a small distortion of the bond distance (relaxing all other coordinates) from the molecule in its stable geometry: One advantage of this definition is that it also gives us a measure of the bond strength. The larger f, the harder it is to stretch the bond, and therefore the stronger it will be. For instance, f for a single covalent C-C bond is around 400 N.m -1 , the triple bond of N2 (one of the strongest bonds in nature) is 2300 N.m -1 , and in rough terms for non-covalent interaction it is usually lower than 100 N.m -1 .