In chemical nomenclature, the prefix "non-" stands for the number nine, for example in molecular chains with nine atoms such as "nonane" for an alkane with nine carbon atoms. The prefixes play a role in the naming of molecules, especially in organic chemistry to indicate the number of similar atoms or groups in the molecule (e.g. "nonan" for 9 carbon atoms, "nonavalent" for nine-valent. Nonapeptides are peptides that consist of nine amino acids.