The development of softwares for the simulation of chemical processes is a tedious work that traditional programming techniques hardly contribute to ease. An object-oriented approach maybe of great help : this paradigm has proved efficient in dramatically increasing extendibility, reusability and reliability of code. Its support to the handling of high-level metaphoric abstractions of the real world transcends Fortran’s expressiveness in power and flexibility. The fundamental abstractions in process simulation relate to the thermodynamic facet of material. We introduce here ATOM, the Applied Thermodynamics Object-oriented Model devoted to the modeling of material’s structure and thermodynamic properties, along with its reusable Object-oriented Algebra Kernel (OAK) describing high-level mathematical structures for low-level numerical applications. ATOM is the core of a new object-oriented dynamic simulator architecture.