Ion exchange chromatography is commonly used in the purification of proteins and other ionic species. Understanding the relationship between the intraparticle conditions and those of the surrounding buffer is crucial for predicting the optimum operating conditions for ion exchange. It is additionally necessary to consider interactions between adsorbed and mobile species. We present a new theoretical model of ion exchange adsorption that incorporates consideration of these interactions as well as the intraparticle conditions and their effect on the diffusing species. This model considers three dimensions of interaction. The ability of the protein to enter to pore is first considered and is affected by the relationship between the molecule hydrodynamic radius and the open pore space. The foot print, or shadow, of a molecule is also a function of the hydrodynamic radius and affects the amount of a particular mobile species that may be adsorbed onto the internal surfaces of the resin. The final area of consideration is the distance of closest approach between the adsorbing species and the charged sites on the resin surface. This parameter is again a function of the molecule's radius as well as the molecular charge and the surrounding conditions. The distance of closest approach indicates the strength of the interaction between the mobile species and resin surface. Our model will incorporate all three of these parameters to predict the adsorption of a protein onto an ion exchange resin. The model is developed from first principles and validated using direct indication of the resin internal pH and adsorption experiments.