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Oxidation states are typically represented by integers which may be positive, zero, or negative. In some cases, the average oxidation state of an element is a fraction, such as 8 / 3 for iron in magnetite Fe 3 O 4 . The highest known oxidation state is reported to be +9, displayed by iridium in the tetroxoiridium(IX) cation (IrO + 4). [1]
See also: oxidation states in {{infobox element}} [ edit ] The oxidation states are also maintained in articles of the elements (of course), and systematically in the table {{ Infobox element/symbol-to-oxidation-state }} (An overview is here ).
The chemical formulas of the oxides of the chemical elements in their highest oxidation state are predictable and are derived from the number of valence electrons for that element. Even the chemical formula of O 4, tetraoxygen, is predictable as a group 16 element.
In contrast to the valency number, the oxidation state can be positive (for an electropositive atom) or negative (for an electronegative atom). Elements in a high oxidation state have an oxidation state higher than +4, and also, elements in a high valence state (hypervalent elements) have a valence higher than 4
Iridium forms compounds in oxidation states between −3 and +9, but the most common oxidation states are +1, +2, +3, and +4. [2] Well-characterized compounds containing iridium in the +6 oxidation state include IrF 6 and the oxides Sr 2 MgIrO 6 and Sr 2 CaIrO 6 .
Percobaltates are chemical compounds where the oxidation state of cobalt is +5. This is the highest established oxidation state of cobalt. [1] The simplest of these are bi-metallic Group 1 oxides such as sodium percobaltate (Na 3 CoO 4); which may be produced by the reaction of cobalt(II,III) oxide and sodium oxide, using oxygen as the oxidant:
Osmium forms compounds with oxidation states ranging from −2 to +8. The most common oxidation states are +2, +3, +4, and +8. The +8 oxidation state is notable for being the highest attained by any chemical element aside from iridium's +9 [1] and is encountered only in xenon, [2] [3] ruthenium, [4] hassium, [5] iridium, [6] and plutonium.
In a Latimer diagram, because by convention redox reactions are shown in the direction of reduction (gain of electrons), the most highly oxidized form of the element is on the left side, with successively lower oxidation states to the right side.