This is a list of known oxidation states of the chemical elements, excluding nonintegral values. The most common states appear in bold. The table is based on that of Greenwood and Earnshaw, with additions noted. Oxidation state 0, which occurs for all elements, is implied by the column with the symbol of the element. The format of the table, which was devised by Mendeleev in 1889, shows the periodicity of the oxidation states of the elements.
A figure with a similar format (shown below) was used by Irving Langmuir in 1919 in one of the early papers about the octet rule. The periodicity of the oxidation states was one of the pieces of evidence that led Langmuir to adopt the rule.
^Ca(I) has been observed; see Krieck, Sven; Görls, Helmar; Westerhausen, Matthias (2010). "Mechanistic Elucidation of the Formation of the Inverse Ca(I) Sandwich Complex [(thf)3Ca(μ-C6H3-1,3,5-Ph3)Ca(thf)3] and Stability of Aryl-Substituted Phenylcalcium Complexes". Journal of the American Chemical Society132 (35): 12492–501. doi:10.1021/ja105534w. PMID20718434.
^Fe(VII) and Fe(VIII) have been reported; see Yurii D. Perfiliev; Virender K. Sharma (2008). "Higher Oxidation States of Iron in Solid State: Synthesis and Their Mössbauer Characterization – Ferrates – ACS Symposium Series (ACS Publications)". Platinum Metals Review48 (4): 157. doi:10.1595/147106704X10801. However, their existence has been disputed.
^Zn(I) has been observed in Zn2Cl2; see Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils; (1985). "Zink". Lehrbuch der Anorganischen Chemie (in German) (91–100 ed.). Walter de Gruyter. pp. 1034–1041. ISBN3-11-007511-3.Cite uses deprecated parameters (help)
^As(I) has been observed in arsenic(I) iodide (AsI); see Ellis, Bobby D.; MacDonald, Charles L. B. (2004). "Stabilized Arsenic(I) Iodide: A Ready Source of Arsenic Iodide Fragments and a Useful Reagent for the Generation of Clusters". Inorganic Chemistry43 (19): 5981–6. doi:10.1021/ic049281s. PMID15360247.
^Cd(I) has been observed in cadmium(I) tetrachloroaluminate (Cd2(AlCl4)2); see Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils; (1985). "Cadmium". Lehrbuch der Anorganischen Chemie (in German) (91–100 ed.). Walter de Gruyter. pp. 1056–1057. ISBN3-11-007511-3.Cite uses deprecated parameters (help)
^I(IV) has been observed in iodine dioxide (IO2); see Pauling, Linus (1988). "Oxygen Compounds of Nonmetallic Elements". General Chemistry (3rd ed.). Dover Publications, Inc. p. 259. ISBN0-486-65622-5.
^Nd(IV) has been observed in unstable solid state compounds; see Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN0-12-352651-5
^Pm(II) has been observed in dilute, solid solutions of promethium dihalides in alkaline earth dihalides; see Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN0-12-352651-5
^Dy(IV) has been observed in unstable solid state compounds; see Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN0-12-352651-5
^Ho(II) has been observed in dilute, solid solutions of holmium dihalides in alkaline earth dihalides; see Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN0-12-352651-5
^Er(II) has been observed in dilute, solid solutions of erbium dihalides in alkaline earth dihalides; see Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN0-12-352651-5
^Os(−1) has been observed in Na 2[Os 4(CO) 13]; see Krause, J.; Siriwardane, Upali; Salupo, Terese A.; Wermer, Joseph R.; Knoeppel, David W.; Shore, Sheldon G. (1993). "Preparation of [Os3(CO)11]2− and its reactions with Os3(CO)12; structures of [Et4N] [HOs3(CO)11] and H2OsS4(CO)". Journal of Organometallic Chemistry454: 263–271. doi:10.1016/0022-328X(93)83250-Y. and Carter, Willie J.; Kelland, John W.; Okrasinski, Stanley J.; Warner, Keith E.; Norton, Jack R. (1982). "Mononuclear hydrido alkyl carbonyl complexes of osmium and their polynuclear derivatives". Inorganic Chemistry21 (11): 3955–3960. doi:10.1021/ic00141a019.
^Ir(VIII) has been observed in iridium tetroxide (IrO4); see Gong, Yu; Zhou, Mingfei; Kaupp, Martin; Riedel, Sebastian (2009). "Formation and Characterization of the Iridium Tetroxide Molecule with Iridium in the Oxidation State +VIII". Angewandte Chemie International Edition48 (42): 7879. doi:10.1002/anie.200902733.
^Ir(IX) has been observed in IrO+ 4; see Wang, Guanjun; Zhou, Mingfei; Goettel, James T.; Schrobilgen, Gary G.; Su, Jing; Li, Jun; Schlöder, Tobias; Riedel, Sebastian (21 August 2014). "Identification of an iridium-containing compound with a formal oxidation state of IX". Nature514: 475–477. doi:10.1038/nature13795.
^Pt(−1) and Pt(−2) have been observed in the barium platinides Ba2Pt, BaPt, and Ba3Pt2 respectively: see Karpov, Andrey; Konuma, Mitsuharu; Jansen, Martin (2006). "An experimental proof for negative oxidation states of platinum: ESCA-measurements on barium platinides". Chemical Communications (8): 838–840. doi:10.1039/b514631c. PMID16479284.
^Tl(−1) has been observed in caesium thallide (CsTl); see Bashilova NI & Khomutova, TV 1984, 'Thallates of alkali metals and monovalent thallium formed in aqueous solutions of their hydroxides', Russian Chemical Bulletin, vol. 33, no. 8, August, pp. 1543–47.
^Bi(I) has been observed in bismuth monobromide (BiBr) and bismuth monoiodide (BiI); see Godfrey, S. M.; McAuliffe, C. A.; Mackie, A. G.; Pritchard, R. G. (1998). Nicholas C. Norman, ed. Chemistry of arsenic, antimony, and bismuth. Springer. pp. 67–84. ISBN0-7514-0389-X.
^Po(V) has been observed in dioxidopolonium(1+) (PoO+ 2); see Thayer, John S. (2010). Chemistry of heavier main group elements. p. 78. doi:10.1007/9781402099755_2.
^Ac(II) is known in actinium dihydride (AcH2); see Farr, J; Giorgi, A.L.; Bowman, M.G.; Money, R.K. (1961). "The crystal structure of actinium metal and actinium hydride". Journal of Inorganic and Nuclear Chemistry18: 42. doi:10.1016/0022-1902(61)80369-2.
^Pa(II) is known in protactinium(II) oxide (PaO); see Sellers, Philip A.; Fried, Sherman; Elson, Robert E.; Zachariasen, W. H. (1954). "The Preparation of Some Protactinium Compounds and the Metal". Journal of the American Chemical Society76 (23): 5935. doi:10.1021/ja01652a011.
^Am(VII) has been observed in AmO5− 6; see Americium, Das Periodensystem der Elemente für den Schulgebrauch (The periodic table of elements for schools) chemie-master.de (in German), Retrieved 28 November 2010 and Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1265. ISBN0080379419.
^Cm(II) has been observed in curium(II) oxide (CmO); see Holleman, Arnold F. and Wiberg, Nils Textbook of Inorganic Chemistry, p.1972, 102 Edition, de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1.
^Cm(VI) has been observed in curium trioxide (CmO3) and dioxidocurium(2+) (CmO2+ 2); see Domanov, V. P.; Lobanov, Yu. V. (October 2011). "Formation of volatile curium(VI) trioxide CmO3". Radiochemistry (SP MAIK Nauka/Interperiodica) 53 (5): 453–6. doi:10.1134/S1066362211050018.
^Cm(VIII) has been observed in curium tetroxide (CmO4); see Domanov, V. P. (January 2013). "Possibility of generation of octavalent curium in the gas phase in the form of volatile tetraoxide CmO4". Radiochemistry (SP MAIK Nauka/Interperiodica) 55 (1): 46–51. doi:10.1134/S1066362213010098.