Formula unit Formula unit A formula unit in chemistry is the empirical formula of any ionic or covalent network solid compound used as an independent entity for stoichiometric calculations. It is the lowest whole number ratio of ions represented in an ionic compound. Examples include ionic NaCl and KO and covalent networks such as SiO and C (as diamond or graphite). Ionic compounds do not exist as individual molecules; a formula unit thus indicates the lowest reduced ratio of ions in the compound. A "chemical formula" shows the kinds and numbers of atoms in the smallest representative unit of a substance. In
Hypothetical chemical compound Hypothetical chemical compound A hypothetical chemical compound is a chemical compound that has been conceived of, but is not known to have been synthesized, observed, or isolated (identified or shown to exist). Some hypothetical compounds cannot form at all. Others might turn out to be highly unstable, decomposing, isomerizing, polymerizing, rearranging, or disproportionating. Some are thought to exist only briefly as reactive intermediates, or in vacuum (helium hydride ion...). Some cannot hold together due to steric hindrance (tetra-"tert"-butylmethane) or bond stress (tetrahedrane...). Some have no known pathway for synthesis (hypercubane...). Some "parent compounds" have not been or cannot be isolated,