Molecular contamination on silicon wafers is mainly determined by the gas phase concentrations of the contaminants, the adsorption energy of the molecules on the surface, and their removal rate. In this paper, a potential energy function is developed to describe interactions between adsorbed molecules and solid surfaces. Ignoring possible chemical reactions at the interface, the development is based on a combination of the Pauli repulsion, the dispersion attraction, and the Coulomb interaction between real and image charges. This potential function will be used to predict adsorption energies of various organic/inorganic molecules, including oxygen, halogens, aliphatic hydrocarbons, acids, and inorganic carbon-containing compounds on silicon wafer surfaces.