CHONS

CHONS is an acronym for carbon, hydrogen, oxygen, nitrogen, and sulfur. It is used in chemistry, biochemistry, and astrobiology as a shorthand for the set of elements most frequently found in biological molecules and in many organic compounds.

In terrestrial life, carbon forms the diverse skeletons of organic molecules. Hydrogen and oxygen are central to water and to many functional groups; nitrogen is essential for amino acids, nucleotides, and many regulatory molecules; sulfur occurs in a subset of amino acids (such as cysteine and methionine) and in some cofactors, enzymes, and vitamins.

The elements in CHONS are among the most abundant in the universe and in Earth’s biosphere. Hydrogen and oxygen are especially common, while carbon provides the backbone of organic chemistry. Nitrogen is widespread in biomolecules, and sulfur, though less abundant, plays critical structural and catalytic roles in proteins.

CHONS is a practical framework rather than a strict boundary, and many biological processes also rely on phosphorus and other elements. The concept helps scientists discuss the chemistry of life and to frame searches for biosignatures in astrobiology, including the detection of organic molecules that contain these elements in space and on other worlds.

Related topics include CHNOPS, organic chemistry, and biochemistry.