A homocycle or homocyclic ring is a ring in which all atoms are of the same chemical element. A heterocycle or heterocyclic ring is a ring containing atoms of at least two different elements, i.e. a non-homocyclic ring. A carbocycle or carbocyclic ring is a homocyclic ring in which all of the atoms are carbon. An important class of carbocycles are alicyclic rings, and an important subclass of these are cycloalkanes.