 Chemists are very permissive about which kinds of mathematical structures can serve as models. But while just about any kind of mathematical structure can serve as a chemical model, different types of systems lend themselves to particular kinds of mathematical structures used in modeling. For example, the most common kinds of mathematical structures employed in quantum chemistry are state spaces, which typically correlate sub-molecular particle distances with the total energy of chemical systems. Other parts of chemical modeling are dynamic, hence they employ trajectory spaces, which can represent the course of a reaction over time. Still other kinds of mathematical structures such as graphs and groups can be employed to model molecular structure and symmetry.