Orthocarbonic acid is the hypothetical acid with the chemical formula H4CO4. In this molecule, a single carbon atom is bonded to four hydroxyl groups. This compound is hypothetical because not even one molecule of this acid has ever been shown to exist. This is because it is highly unstable, decomposing into carbon dioxide and water. This acid is tetraprotic (has four dissociable protons), and thus could form four types of salts, as demonstrated by the series NaH3CO4, Na2H2CO4, Na3HCO4, and Na4CO4. The analogous orthosilicic acid is well known. Other examples of hypothetical compounds so unstable as not to have been shown to exist are ammonium nitride, (NH4)3N, and bromine hepta-fluoride, BrF7.