Chemical species

Chemical species are a specific form of chemical substance or chemically identical molecular entities that have the same molecular energy level at a specified timescale. These entities are classified through bonding types and relative abundance of isotopes. Types of chemical species can be classified based on the type of molecular entity and can be either an atomic, molecular, ionic or radical species.

Classification

Generally, a chemical species is defined as a chemical identity that has the same set of molecular energy levels in a defined timescale (i.e. an experiment). These energy levels determine the way the chemical species will interact with others through properties such as bonding or isotopic compositions. The chemical species can be an atom, molecule, ion, or radical, with a specific chemical name and chemical formula.

In supramolecular chemistry, chemical species are structures created by forming or breaking bonds between molecules, such as hydrogen bonding or dipole-dipole bonds. These types of bonds can determine the physical property of chemical species in a liquid or solid state.

A single chemical can classified as two different types of species. For example, nitrate is both a molecular and ionic species, with its formula being NO₃−.

The term "chemical species" is also applied to a set of chemically identical atomic or molecular structures in a solid compound.^{[citation needed]}

DNA is not a species; the name is generically applied to many molecules of different formulas, as each DNA molecule is unique.

Types of chemical species

Atomic species

An atomic species is a specific form of an element defined by the atom's isotope, electronic or oxidation state. Argon is an atomic species of formula Ar.

Molecular species

Molecular species are groups of atoms that are held together by chemical bonds. One example is ozone, which has the chemical formula O₃.

Ionic species

Ionic species are atoms or molecules that have gained or lost electrons, resulting in a net electrical charge that can be either positively (cation) or negatively charged (anion).

Species with an overall positive charge will be a cationic species. The sodium ion is an example of a cationic species, and its formula is Na⁺.^{[citation needed]} Species with an overall negative charge will be an anionic species. Chloride is an anionic species, and its formula is Cl⁻.

Radical species

Radical species are atoms or molecules with unpaired electrons. For example, the triarylborane anion is a radical species, and its formula is Ar₃B⁻.