Three-parameter Lennard-Jones and Morse interatomic potentials are the simplest ones, which can be used to describe thermophysical properties of the liquid and solid substances. Upon adjusting the model parameters to real substance properties, the interatomic potentials can be used to describe simple single-component substance with good accuracy. Usually, these tree parameters can be found from the cohesion energy, bulk moduli, and the molar volume data or the lattice parameters obtained experimentally for chemically-pure crystalline solids. In our paper, in case of chemically-different atoms, for both the Lennard-Jones potential and the Morse one, or any other three-parameter potential, we propose some convenient model relationships expressing the corresponding three parameters through the previously found ones for pure chemical elements.