Oxidation number

Oxidation number
Oxidation numbers of carbon and hydrogen in ethane

In coordination chemistry, the oxidation number of a central atom in a coordination compound is the charge that it would have if all the ligands were removed along with the electron pairs that were shared with the central atom.[1] Oxidation numbers are often confused with oxidation states.

The oxidation number is used in the nomenclature of inorganic compounds. It is represented by a Roman numeral. The oxidation number is placed either as a right superscript to the element symbol, for example FeIII, or in parentheses after the name of the element, iron(III): in the latter case, there is no space between the element name and the oxidation number.


Oxidation number versus oxidation state

The oxidation number is usually numerically equal to the oxidation state and so the terms oxidation state and oxidation number are often used interchangeably. However, oxidation number is used in coordination chemistry with a slightly different meaning since the rules used for counting electrons are different: every electron belongs to the ligand, regardless of electronegativity. Also, oxidation numbers are conventionally represented with Roman numerals while oxidation states are given in Arabic numerals. The oxidation number of a central atom may be part of the compound's name (for example iron(II,III) oxide); the oxidation state of atoms is not included in compound names.

The oxidation state can differ from the oxidation number in a few cases where the ligand atom is less electronegative than the central atom (e.g., in iridium phosphine complexes), resulting in a formal oxidation state that is different from the oxidation number.[citation needed]

Spectroscopic oxidation states

Although formal oxidation numbers can be helpful for classifying compounds, they are unmeasurable and their physical meaning can be ambiguous. Formal oxidation numbers require particular caution for molecules where the bonding is covalent, since the formal oxidation numbers require the heterolytic removal of ligands, which essentially denies covalency. Spectroscopic oxidation states, as defined by Jorgenson and reiterated by Wieghardt, are measurables that are bench-marked using spectroscopic and crystallographic data.[2]

See also


  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "oxidation number".
  2. ^ Bill, E.; Bothe, E.; Chaudhuri, P.; Chlopek, K.; Herebian, D.; Kokatam, S.; Ray, K.; Weyhermueller, T.; Neese, F.; Wieghardt, K. (2005). "Molecular and electronic structure of four- and five-coordinate cobalt complexes containing two o-phenylenediamine- or two o-aminophenol-type ligands at various oxidation levels functional, and correlated ab initio study". Chemistry - A European Journal 11 (1): 204–224. doi:10.1002/chem.200400850. PMID 15549762. 

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • oxidation number — ▪ chemistry also called  Oxidation State,        the total number of electrons (electron) that an atom either gains or loses in order to form a chemical bond (chemical bonding) with another atom.       Each atom that participates in an oxidation… …   Universalium

  • oxidation number — a number assigned to each atom in a molecule or ion that represents the number of electrons theoretically gained (positive oxidation numbers) or lost (negative numbers) in converting the atom to the elemental form. Oxidation numbers are assigned… …   Medical dictionary

  • oxidation number — noun the degree of oxidation of an atom or ion or molecule; for simple atoms or ions the oxidation number is equal to the ionic charge the oxidation number of hydrogen is +1 and of oxygen is 2 • Syn: ↑oxidation state • Hypernyms: ↑number …   Useful english dictionary

  • oxidation number — oksidacijos laipsnis statusas T sritis chemija apibrėžtis Sąlyginis atomo krūvis junginyje, kurį atomas įgytų netekdamas (prisijungdamas) valentinių elektronų. atitikmenys: angl. oxidation degree; oxidation number; valence number rus. степень… …   Chemijos terminų aiškinamasis žodynas

  • oxidation number — (also oxidation state) noun Chemistry a number representing the number of electrons lost or gained by an atom of a particular element when chemically combined …   English new terms dictionary

  • oxidation number — noun see oxidation state …   New Collegiate Dictionary

  • oxidation number — /ɒksəˈdeɪʃən nʌmbə/ (say oksuh dayshuhn numbuh) noun a number representing the electric charges that the atom would have if the electrons in a compound were assigned to the atoms in a conventional way, as FeCl3, where the ferric ion has three… …   Australian English dictionary

  • oxidation number — noun the net sum of the negative, less the positive, charges on an atom …   Wiktionary

  • Oxidation state — Not to be confused with Oxidation number. In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds… …   Wikipedia

  • oxidation–reduction reaction — ▪ chemical reaction Introduction also called  redox reaction        any chemical reaction in which the oxidation number of a participating chemical species changes. The term covers a large and diverse body of processes. Many oxidation– reduction… …   Universalium

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.