Editing Module:Carbonate (section)

==Structure and bonding==

The carbonate ion is the simplest [[oxocarbon anion]]. It consists of one [[carbon]] atom surrounded by three [[oxygen]] atoms, in a [[trigonal planar]] arrangement, with ''D''<sub>3h</sub> [[Molecular symmetry#Point Group|molecular symmetry]]. It has a molecular mass of 60.01&nbsp;[[Molar mass|g/mol]] and carries a total [[formal charge]] of −2. It is the [[conjugate acid|conjugate base]] of the [[bicarbonate|hydrogencarbonate (bicarbonate)]]<ref>{{Citation |url = http://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf |title = Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005 |publisher = IUPAC |page = 137 |url-status = live |archive-url = https://web.archive.org/web/20170518230415/http://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf |archive-date = 2017-05-18}}</ref> ion, {{chem2|HCO3-}}, which is the conjugate base of {{chem2|H2CO3}}, [[carbonic acid]].

The [[Lewis structure]] of the carbonate ion has two (long) single bonds to negative oxygen atoms, and one short double bond to a neutral oxygen atom.

:[[File:Carbonate-ion-localised-2D.png|100px|Simple, localised Lewis structure of the carbonate ion|class=skin-invert-image]]

This structure is incompatible with the observed symmetry of the ion, which implies that the three bonds are the same length and that the three oxygen atoms are equivalent. As in the case of the [[isoelectronic]] [[nitrate]] ion, the symmetry can be achieved by a [[resonance (chemistry)|resonance]] among three structures:

:[[File:Carbonate-ion-resonance-2D.png|400px|Resonance structures of the carbonate ion|class=skin-invert-image]]

This resonance can be summarized by a model with fractional bonds and [[delocalization|delocalized]] charges:

:[[File:Carbonate-ion-delocalised-partial-charges-2D.png|120px|Delocalisation and partial charges on the carbonate ion|class=skin-invert-image]] [[File:Carbonate-3D-vdW.png|80px|Space-filling model of the carbonate ion]]