Chemical species

Chemical species are atoms, molecules, molecular fragments, ions, etc., subjected to a chemical process or to a measurement. Generally, a chemical species is an ensemble of chemically identical molecular entities that can explore the same set of molecular energy levels on a characteristic or delineated time scale. The term may be applied equally to a set of chemically identical atomic or molecular structural units.

In supramolecular chemistry, chemical species are those supramolecular structures whose interactions and associations are brought about via intermolecular bonding and debonding actions, and function to form the basis of this branch of chemistry.