Molecular entity

{{short description|Any type of particle that can undergo a chemical process}}

In chemistry and physics, a molecular entity, or chemical entity, is "any constitutionally or isotopically distinct atom, molecule, ion, ion pair, radical, radical ion, complex, conformer, etc., identifiable as a separately distinguishable entity".{{GoldBookRef|title=molecular entity|file=M03986}}

A molecular entity is any singular entity, irrespective of its nature, used to concisely express any type of chemical particle that can exemplify some process: for example, atoms, molecules, ions, etc. can all undergo a chemical reaction.{{cn|date=May 2025}}

Chemical species is the macroscopic equivalent of molecular entity and refers to sets or ensembles of molecular entities.{{cn|date=May 2025}}

According to IUPAC, "The degree of precision necessary to describe a molecular entity depends on the context. For example 'hydrogen molecule' is an adequate definition of a certain molecular entity for some purposes, whereas for others it is necessary to distinguish the electronic state and/or vibrational state and/or nuclear spin, etc. of the hydrogen molecule."{{cn|date=May 2025}}