bond order of the individual links between ring atoms, and their arrangements within the rings, cyclic compounds may be aromatic or non-aromatic; in the case of non-aromatic cyclic compounds, they may vary from being fully saturated to having varying numbers of multiple bonds. As a consequence of the constitutional variability that is thermodynamically possible in cyclic structures, the number of possible cyclic structures, even of small size (e.g., <17 atoms) numbers in the many billions. Moreover, the closing of atoms into rings may lock particular functional group–substituted atoms into place, resulting in stereochemistry and chirality being associated with the compound, including some manifestations that are unique to rings (e.g., configurational isomers); As well, depending on ring size, the three-dimensional shapes of particular cyclic structures — typically rings of five atoms and larger — can vary and interconvert such that conformational isomerism is displayed. Carbocycles The vast majority of cyclic compounds are organic, and of these, a significant and conceptually important portion are composed of rings made only of carbon atoms (i.e., they are carbocycles). Inorganic cyclic compounds Inorganic atoms form cyclic compounds as well. Examples include sulfur (e.g. in polysulfides), silicon (e.g., in silanes), phosphorus (e.g., in phosphanes, metaphosphates and other phosphoric acid derivatives), and boron (e.g., in triboric acid). When carbon in benzene is "replaced" by other elements, e.g., as in borabenzene, silabenzene, germanabenzene, stannabenzene, and phosphorine, aromaticity is retained, and so aromatic inorganic cyclic compounds are also known and well-characterized. Heterocyclic compounds Cyclic compounds that have both carbon and non-carbon atoms present are termed heterocyclic compounds; alternatively the name can refer to inorganic cyclic compounds, such as siloxanes and borazines, that have more than one type of atom in their rings. Hantzsch–Widman nomenclature is recommended by the IUPAC for naming heterocycles, but many common names remain in regular use. Macrocycles The term macrocycle is used for compounds having a rings of 8 or more atoms. Macrocycles may be fully carbocyclic, heterocyclic but having limited heteroatoms (e.g., in lactones and lactams), or be rich in heteroatoms and displaying significant symmetry (e.g., in the case of chelating macrocycles). Macrocycles can access a number of stable conformations, with preference to reside in conformations that minimize transannular nonbonded interactions within the ring (e.g., with the chair and chair-boat being more stable than the boat-boat conformation for cyclooctane, because of the interactions depicted by the arcs shown). Medium rings (8-11 atoms) are the