Particle inception is modeled by a nucleation reaction. A nucleation reaction is a special type of surface reaction detailing the formation and the properties of the new particles. It is irreversible and all reactants must be gas phase species. These gas phase reactants are the precursors; they can be different gas species, that is, hetero-molecular nucleation, or the same gas species, that is, homo-molecular nucleation. Because new surface area is created when new particles are formed, the nucleation reaction need not conserve surface sites.

The use of a reaction form to represent particle inception has several advantages. Because the reaction data of the nucleation process are presented in text format, they are easy to comprehend and to transfer. The gas phase precursors from which the new particles are created can be easily identified in the reaction. The chemical composition of the particle core is defined by the bulk product of nucleation reaction, and the particle class of the nuclei is given by the stoichiometric coefficient of the bulk product. The initial coverage on the new particle surface, that is, species/atoms that bond to the particle core, is indicated by the ratio of the stoichiometric coefficients of surface species products. Moreover, since the nucleation reaction is given as part of the surface reaction mechanism, conservation of element and mass is checked by the interpreter.