The part of a molecule that makes it exist in left- and right-handed forms. In most cases this is a chirality centre (i.e. an asymmetric atom). In certain cases the element is a chirality axis. For example, in allenenes of the type R₁R₂C=C=CR₃R₄ the C=C=C chain is a chirality axis. Certain ring compounds may display chirality as a result of a chirality plane in the molecule.