List of oxidation states of the elements

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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,[1] 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 Dmitri Mendeleev in 1889, shows the periodicity of the oxidation states of the elements.[1]

List[edit]

  Element
  Noble gas
Z Element Negative
oxidation
states
  Positive
oxidation
states
Group Notes
−9−5 −9−4 −9−3 −9−2 −9−1 _0 _+1 _+2 _+3 _+4 _+5 _+6 _+7 _+8 _+9
1 hydrogen −1−1 H +1+1+1 1
2 helium He 18
3 lithium Li +1+1+1 1 [2]
4 beryllium Be +1 +2+2 2 [3]
5 boron −5 −1 B +1 +2 +3+3 13 [4][5]
6 carbon −4−4 −3−3 −2−2 −1−1 C +1+1+1 +2+2 +3+3 +4+4 14
7 nitrogen −3−3 −2 −1 N +1 +2 +3+3 +4 +5+5 15
8 oxygen −2−2 −1 O +1 +2 16
9 fluorine −1−1 F 17
10 neon Ne 18
11 sodium −1 Na +1+1+1 1 [2]
12 magnesium Mg +1 +2+2 2 [6]
13 aluminium −2 −1 Al +1 +2 +3+3 13 [7][8][9]
14 silicon −4−4 −3 −2 −1 Si +1 +2 +3 +4+4 14
15 phosphorus −3−3 −2 −1 P +1 +2 +3+3 +4 +5+5 15
16 sulfur −2−2 −1 S +1 +2+2 +3 +4+4 +5 +6+6 16
17 chlorine −1−1 Cl +1+1+1 +2 +3+3 +4 +5+5 +6 +7+7 17 [10]
18 argon Ar 18
19 potassium −1 K +1+1+1 1 [2]
20 calcium Ca +1 +2+2 2 [11]
21 scandium Sc +1 +2 +3+3 3 [12][13]
22 titanium −2 −1 Ti +1 +2 +3 +4+4 4 [14][15][16]
23 vanadium −3 −1 V +1 +2 +3 +4 +5+5 5 [15]
24 chromium −4 −2 −1 Cr +1 +2 +3+3 +4 +5 +6+6 6 [15]
25 manganese −3 −2 −1 Mn +1 +2+2 +3 +4+4 +5 +6 +7+7 7
26 iron −4 −2 −1 Fe +1 +2+2 +3+3 +4 +5 +6+6 +7 8 [17][18][19]
27 cobalt −3 −1 Co +1 +2+2 +3+3 +4 +5 9 [15]
28 nickel −2 −1 Ni +1 +2+2 +3 +4 10 [20]
29 copper −2 Cu +1 +2+2 +3 +4 11 [19]
30 zinc −2 Zn +1 +2+2 12 [19][21]
31 gallium −5 −4 −2 −1 Ga +1 +2 +3+3 13 [8][22]
32 germanium −4−4 −3 −2 −1 Ge +1 +2+2 +3 +4+4 14 [23]
33 arsenic −3−3 −2 −1 As +1 +2 +3+3 +4 +5+5 15 [8][24][25]
34 selenium −2−2 −1 Se +1 +2+2 +3 +4+4 +5 +6+6 16 [26][27][28][29]
35 bromine −1−1 Br +1+1+1 +3+3 +4 +5+5 +7+7 17
36 krypton Kr +2+2 18
37 rubidium −1 Rb +1+1+1 1 [2]
38 strontium Sr +1 +2+2 2 [30]
39 yttrium Y +1 +2 +3+3 3 [31][32]
40 zirconium −2 Zr +1 +2 +3 +4+4 4 [15][33]
41 niobium −3 −1 Nb +1 +2 +3 +4 +5+5 5 [15][34]
42 molybdenum −4 −2 −1 Mo +1 +2 +3 +4+4 +5 +6+6 6 [15]
43 technetium −3 −1 Tc +1 +2 +3 +4+4 +5 +6 +7+7 7
44 ruthenium −4 −2 Ru +1 +2 +3+3 +4+4 +5 +6 +7 +8 8 [15][19]
45 rhodium −3 −1 Rh +1 +2 +3+3 +4 +5 +6 9 [15]
46 palladium Pd +1 +2+2 +3 +4+4 +5 +6 10 [35][36][37][38]
47 silver −2 −1 Ag +1+1+1 +2 +3 +4 11 [19][39][40]
48 cadmium −2 Cd +1 +2+2 12 [19][41]
49 indium −5 −2 −1 In +1 +2 +3+3 13 [8][42][43]
50 tin −4−4 −3 −2 −1 Sn +1 +2+2 +3 +4+4 14 [8][44][45]
51 antimony −3−3 −2 −1 Sb +1 +2 +3+3 +4 +5+5 15 [8][46][47][48]
52 tellurium −2−2 −1 Te +1 +2+2 +3 +4+4 +5 +6+6 16 [8][49][50][51]
53 iodine −1−1 I +1+1+1 +3+3 +4 +5+5 +6 +7+7 17 [52][53]
54 xenon Xe +2+2 +4+4 +6+6 +8 18 [54]
55 caesium −1 Cs +1+1+1 1 [2]
56 barium Ba +1 +2+2 2 [55]
57 lanthanum La +1 +2 +3+3 3 [56]
58 cerium Ce +2 +3+3 +4+4
59 praseodymium Pr +2 +3+3 +4 +5 [57]
60 neodymium Nd +2 +3+3 +4 [58]
61 promethium Pm +2 +3+3 [59]
62 samarium Sm +2 +3+3
63 europium Eu +2+2 +3+3
64 gadolinium Gd +1 +2 +3+3
65 terbium Tb +1 +2 +3+3 +4 [59]
66 dysprosium Dy +2 +3+3 +4 [60]
67 holmium Ho +2 +3+3 [59]
68 erbium Er +2 +3+3 [59]
69 thulium Tm +2 +3+3
70 ytterbium Yb +2 +3+3
71 lutetium Lu +2 +3+3 [59]
72 hafnium −2 Hf +1 +2 +3 +4+4 4 [15][61]
73 tantalum −3 −1 Ta +1 +2 +3 +4 +5+5 5 [15][34]
74 tungsten −4 −2 −1 W +1 +2 +3 +4+4 +5 +6+6 6 [15]
75 rhenium −3 −1 Re +1 +2 +3 +4+4 +5 +6 +7 7
76 osmium −4 −2 −1 Os +1 +2 +3 +4+4 +5 +6 +7 +8 8 [19][62]
77 iridium −3 −1 Ir +1 +2 +3+3 +4+4 +5 +6 +7 +8 +9 9 [63][64][65][66]
78 platinum −3 −2 −1 Pt +1 +2+2 +3 +4+4 +5 +6 10 [19][67][68]
79 gold −3 −2 −1 Au +1 +2 +3+3 +5 11 [19]
80 mercury −2 Hg +1+1+1 +2+2 12 [19]
81 thallium −5 −2 −1 Tl +1+1+1 +2 +3+3 13 [8][69][70][71]
82 lead −4 −2 −1 Pb +1 +2+2 +3 +4+4 14 [8][72][73]
83 bismuth −3 −2 −1 Bi +1 +2 +3+3 +4 +5 15 [74][75][76][77]
84 polonium −2−2 Po +2+2 +4+4 +5 +6 16 [78]
85 astatine −1−1 At +1+1+1 +3 +5 +7 17
86 radon Rn +2+2 +6 18 [79][80][81]
87 francium Fr +1+1+1 1
88 radium Ra +2+2 2
89 actinium Ac +3+3 3
90 thorium Th +1 +2 +3 +4+4 [82][83]
91 protactinium Pa +3 +4 +5+5
92 uranium U +1 +2 +3 +4 +5 +6+6 [84][85]
93 neptunium Np +2 +3 +4 +5+5 +6 +7 [86]
94 plutonium Pu +2 +3 +4+4 +5 +6 +7 [87]
95 americium Am +2 +3+3 +4 +5 +6 +7 [88]
96 curium Cm +3+3 +4 +6 [89][90]
97 berkelium Bk +3+3 +4
98 californium Cf +2 +3+3 +4
99 einsteinium Es +2 +3+3 +4 [91]
100 fermium Fm +2 +3+3
101 mendelevium Md +2 +3+3
102 nobelium No +2+2 +3
103 lawrencium Lr +3+3
104 rutherfordium Rf +4+4 4
105 dubnium Db +5+5 5 [92]
106 seaborgium Sg +6+6 6 [93]
107 bohrium Bh +7+7 7 [94]
108 hassium Hs +8+8 8 [95]
109 meitnerium Mt 9
110 darmstadtium Ds 10
111 roentgenium Rg 11
112 copernicium Cn +2 12 [96]
113 nihonium Nh 13
114 flerovium Fl 14
115 moscovium Mc 15
116 livermorium Lv 16
117 tennessine Ts 17
118 oganesson Og 18

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.[97] The periodicity of the oxidation states was one of the pieces of evidence that led Langmuir to adopt the rule.

Langmuir valence.png

References and notes[edit]

  1. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 27–28. ISBN 0-08-037941-9. 
  2. ^ a b c d e Na(−1), K(−1), Rb(−1), and Cs(−1) are known in alkalides; the table by Greenwood and Earnshaw shows −1 only for Na and also erroneously for Li; no lithides are described.
  3. ^ Be(I) has been observed in beryllium monohydride (BeH); see Shayesteh, A.; Tereszchuk, K.; Bernath, P. F.; Colin, R. (2003). "Infrared Emission Spectra of BeH and BeD" (PDF). J. Chem. Phys. bernath.uwaterloo.ca. 118 (3): 1158. doi:10.1063/1.1528606. Archived from the original (PDF) on 2007-12-02. Retrieved 2007-12-10. 
  4. ^ B(−1) has been observed in magnesium diboride (MgB2), see James Keeler, Peter Wothers (2014). Chemical Structure and Reactivity: An Integrated Approach. Oxford University Press. 
  5. ^ B(−5) has been observed in Al3BC, see Melanie Schroeder. "Eigenschaften von borreichen Boriden und Scandium-Aluminium-Oxid-Carbiden" (PDF) (in German). p. 139. 
  6. ^ Low valent magnesium compounds with Mg(I) have been obtained using bulky ligands; see Green, S. P.; Jones C.; Stasch A. (December 2007). "Stable Magnesium(I) Compounds with Mg-Mg Bonds". Science. 318 (5857): 1754–1757. Bibcode:2007Sci...318.1754G. PMID 17991827. doi:10.1126/science.1150856. 
  7. ^ Al(II) has been observed in aluminium(II) oxide (AlO); see D. C. Tyte (1964). "Red (B2Π–A2σ) Band System of Aluminium Monoxide". Nature. 202 (4930): 383–384. Bibcode:1964Natur.202..383T. doi:10.1038/202383a0. , and in dialanes (R2Al—AlR2); see Uhl, Werner "Organoelement Compounds Possessing Al—Al, Ga—Ga, In—In, and Tl—Tl Single Bonds" Advances in Organometallic Chemistry Volume 51, 2004, Pages 53–108. doi:10.1016/S0065-3055(03)51002-4
  8. ^ a b c d e f g h i Negative oxidation states of p-block metals (Al, Ga, In, Sn, Tl, Pb, Bi, Po) and metalloids (Si, Ge, As, Sb, Te, At) may occur in Zintl phases, see: [1], p. 259 and [2] (both in German).
  9. ^ Al(−2) has been observed in Sr14[Al4]2[Ge]3, see Wemdorff, Marco; Röhr, Caroline (2007). "Sr14[Al4]2[Ge]3: Eine Zintl-Phase mit isolierten [Ge]4–- und [Al4]8–-Anionen / Sr14[Al4]2[Ge]3: A Zintl Phase with Isolated [Ge]4–- and [Al4]8– Anions". Zeitschrift für Naturforschung B (in German). 62 (10): 1227. doi:10.1515/znb-2007-1001. 
  10. ^ The equilibrium Cl2O6⇌2ClO3 is mentioned by Greenwood and Earnshaw, but it has been refuted, see Lopez, Maria; Juan E. Sicre (1990). "Physicochemical properties of chlorine oxides. 1. Composition, ultraviolet spectrum, and kinetics of the thermolysis of gaseous dichlorine hexoxide". J. Phys. Chem. 94 (9): 3860–3863. doi:10.1021/j100372a094. , and Cl2O6 is actually chlorine(V,VII) oxide. However, ClO3 has been observed, see Grothe, Hinrich; Willner, Helge (1994). "Chlorine Trioxide: Spectroscopic Properties, Molecular Structure, and Photochemical Behavior". Angew. Chem. Int. Ed. 33 (14): 1482–1484. doi:10.1002/anie.199414821. 
  11. ^ 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 Society. 132 (35): 12492–501. PMID 20718434. doi:10.1021/ja105534w. 
  12. ^ Sc(I) has been observed; see Polly L. Arnold; F. Geoffrey; N. Cloke; Peter B. Hitchcock & John F. Nixon (1996). "The First Example of a Formal Scandium(I) Complex:  Synthesis and Molecular Structure of a 22-Electron Scandium Triple Decker Incorporating the Novel 1,3,5-Triphosphabenzene Ring". J. Am. Chem. Soc. 118 (32): 7630–7631. doi:10.1021/ja961253o. 
  13. ^ Sc(II) has been observed; see Woen, David H.; Chen, Guo P.; Ziller, Joseph W.; Boyle, Timothy J.; Furche, Filipp; Evans, William J. (January 2017). "Solution Synthesis, Structure, and CO Reduction Reactivity of a Scandium(II) Complex". Angewandte Chemie International Edition. 56: 2050–2053. doi:10.1002/anie.201611758. 
  14. ^ Ti(I) has been observed in [Ti(η6-1,3,5-C6H3iPr3)2][BAr4] (Ar = C6H5, p-C6H4F, 3,5-C6H3(CF3)2); see Fausto Calderazzo, Isabella Ferri, Guido Pampaloni, Ulli Englert, Malcolm L. H. Green (1997). "Synthesis of [Ti(η6-1,3,5-C6H3iPr3)2][BAr4] (Ar = C6H5, p-C6H4F, 3,5-C6H3(CF3)2), the First Titanium(I) Derivatives". Organometallics. 16 (14): 3100–3101. doi:10.1021/om970155o. 
  15. ^ a b c d e f g h i j k l Ti(−2), V(−3), Cr(−4), Co(−3), Zr(−2), Nb(−3), Mo(−4), Ru(−2), Rh(−3), Hf(−2), Ta(−3), and W(−4) occur in anionic binary metal carbonyls; see [3], p. 4 (in German); [4], pp. 97–100; [5], p. 239
  16. ^ Ti(−1) has been reported in [Ti(bipy)3], but was later shown to be Ti(+3); see Bowman, A. C.; England, J.; Sprouls, S.; Weihemüller, T.; Wieghardt, K. (2013). "Electronic structures of homoleptic [tris(2,2'-bipyridine)M]n complexes of the early transition metals (M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta; n = 1+, 0, 1-, 2-, 3-): an experimental and density functional theoretical study.". Inorganic Chemistry. 52 (4): 2242–56. PMID 23387926. doi:10.1021/ic302799s.  However, Ti(−1) occurs in [Ti(η-C6H6] and [Ti(η-C6H5CH3)], see Bandy, J. A.; Berry, A.; Green, M. L. H.; Perutz, R. N.; Prout, K.; Verpeautz, J.-N. (1984). "Synthesis of anionic sandwich compounds: [Ti(η-C6H5R)2] and the crystal structure of [K(18-crown-6)(µ-H)Mo(η-C5H5)2]". Inorganic Chemistry. 52 (4): 729–731. doi:10.1039/C39840000729. 
  17. ^ Fe(VII) has been observed in [FeO4]; see Lu, Jun-Bo; Jian, Jiwen; Huang, Wei; Lin, Hailu; Zhou, Mingfei (2016). "Experimental and theoretical identification of the Fe(VII) oxidation state in FeO4". Physical Chemistry Chemical Physics. 18: 31125–31131. doi:10.1039/C6CP06753K. 
  18. ^ Fe(VIII) has 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 Review. 48 (4): 157–158. doi:10.1595/147106704X10801.  However, its existence has been disputed.
  19. ^ a b c d e f g h i j Fe(−4), Ru(−4), and Os(−4) have been observed in metal-rich compounds containing octahedral complexes [MIn6−xSnx]; Pt(−3) (as a dimeric anion [Pt–Pt]6−), Cu(−2), Zn(−2), Ag(−2), Cd(−2), Au(−2), and Hg(−2) have been observed (as dimeric and monomeric anions; dimeric ions were initially reported to be [T–T]2− for Zn, Cd, Hg, but later shown to be [T–T]4− for all these elements) in La2Pt2In, La2Cu2In, Ca5Au3, Ca5Ag3, Ca5Hg3, Sr5Cd3, Ca5Zn3(structure (AE2+)5(T–T)4−T2−⋅4e), Yb3Ag2, Ca5Au4, and Ca3Hg2; Au(–3) has been observed in ScAuSn and in other 18-electron half-Heusler compounds. See Changhoon Lee; Myung-Hwan Whangbo (2008). "Late transition metal anions acting as p-metal elements". Frontiers in Solid State Chemistry. 10 (4): 444–449. doi:10.1016/j.solidstatesciences.2007.12.001.  and Changhoon Lee; Myung-Hwan Whangbo; Jürgen Köhler (2010). "Analysis of Electronic Structures and Chemical Bonding of Metal-rich Compounds. 2. Presence of Dimer (T–T)4– and Isolated T2– Anions in the Polar Intermetallic Cr5B3-Type Compounds AE5T3 (AE = Ca, Sr; T = Au, Ag, Hg, Cd, Zn)". ZAAC. 636 (1): 36–40. doi:10.1002/zaac.200900421. 
  20. ^ Ni(−2) has been observed in Li2[Ni(1,5-COD)2], see Jonas, Klaus (1975). "Dilithium-Nickel-Olefin Complexes. Novel Bimetal Complexes Containing a Transition Metal and a Main Group Metal". Angew. Chem. Int. Ed. 14 (11): 752–753. doi:10.1002/anie.197507521.  and Ellis, John E. (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8): 3167–86. doi:10.1021/ic052110i. 
  21. ^ Zn(I) has been observed in decamethyldizincocene (Zn25–C5Me5)2); see Resa, I.; Carmona, E.; Gutierrez-Puebla, E.; Monge, A. (2004). "Decamethyldizincocene, a Stable Compound of Zn(I) with a Zn-Zn Bond". Science. 305 (5687): 1136–8. PMID 15326350. doi:10.1126/science.1101356. 
  22. ^ Ga(−2), Ga(−4), and Ga(−5) have been observed in the magnesium gallides MgGa, Mg2Ga, and Mg5Ga2, respectively; see Patrick Hofmann. "Colture. Ein Programm zur interaktiven Visualisierung von Festkörperstrukturen sowie Synthese, Struktur und Eigenschaften von binären und ternären Alkali- und Erdalkalimetallgalliden" (PDF) (in German). p. 72. 
  23. ^ Ge(−1), Ge(−2), and Ge(−3) have been observed in germanides; see Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils (1995). "Germanium". Lehrbuch der Anorganischen Chemie (in German) (101 ed.). Walter de Gruyter. pp. 953–959. ISBN 3-11-012641-9. .
  24. ^ 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 Chemistry. 43 (19): 5981–6. PMID 15360247. doi:10.1021/ic049281s. 
  25. ^ As(IV) has been observed in arsenic(IV) hydroxide (As(OH)4) and HAsO
    3
    ; see Kläning, Ulrik K.; Bielski, Benon H. J.; Sehested, K. (1989). "Arsenic(IV). A pulse-radiolysis study". Inorganic Chemistry. 28 (14): 2717–24. doi:10.1021/ic00313a007. 
  26. ^ Se(−1) has been observed in diselenides(2−) (Se22−).
  27. ^ Se(I) has been observed in selenium(I) chloride (Se2Cl2); see "Selenium : Selenium(I) chloride compound data". WebElements.com. Retrieved 2007-12-10. 
  28. ^ Se(III) has been observed in Se2NBr3; see Lau, Carsten; Neumüller, Bernhard; Vyboishchikov, Sergei F.; Frenking, Gernot; Dehnicke, Kurt; Hiller, Wolfgang; Herker, Martin (1996). "Se2NBr3, Se2NCl5, Se2NCl6: New Nitride Halides of Selenium(III) and Selenium(IV)". Chemistry: A European Journal. 2: 1393–1396. doi:10.1002/chem.19960021108. 
  29. ^ Se(V) has been observed in SeO2−
    3
    and HSeO2−
    4
    ; see Kläning, Ulrik K.; Sehested, K. (1986). "Selenium(V). A pulse radiolysis study". Inorganic Chemistry. 90 (21): 5460–4. doi:10.1021/j100412a112. 
  30. ^ Sr(I) has been observed in strontium monofluoride (SrF); see P. Colarusso; Guo, B.; Zhang, K.-Q.; Bernath, P.F.; et al. (1996). "High-Resolution Infrared Emission Spectrum of Strontium Monofluoride" (PDF). J. Molecular Spectroscopy. 175: 158–171. Bibcode:1996JMoSp.175..158C. doi:10.1006/jmsp.1996.0019. Archived from the original (PDF) on 2012-03-08. 
  31. ^ Y(I) has been observed in yttrium(I) bromide (YBr); see "Yttrium: yttrium(I) bromide compound data". OpenMOPAC.net. Archived from the original on 2011-07-23. Retrieved 2007-12-10. 
  32. ^ Y(II) has been observed in [(18-crown-6)K][(C5H4SiMe3)3Y]; see MacDonald, M. R.; Ziller, J. W.; Evans, W. J. (2011). "Synthesis of a Crystalline Molecular Complex of Y2+, [(18-crown-6)K][(C5H4SiMe3)3Y].". J. Am. Chem. Soc. 133 (40): 15914–17. doi:10.1021/ja207151y. 
  33. ^ Zr(−1) has been reported in [Zr(bipy)3] (see Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 960. ISBN 0-08-037941-9.  and Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils (1995). "Zirconium". Lehrbuch der Anorganischen Chemie (in German) (101 ed.). Walter de Gruyter. p. 1413. ISBN 3-11-012641-9. ), but was later shown to be Zr(+4); see Bowman, A. C.; England, J.; Sprouls, S.; Weihemüller, T.; Wieghardt, K. (2013). "Electronic structures of homoleptic [tris(2,2'-bipyridine)M]n complexes of the early transition metals (M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta; n = 1+, 0, 1-, 2-, 3-): an experimental and density functional theoretical study.". Inorganic Chemistry. 52 (4): 2242–56. PMID 23387926. doi:10.1021/ic302799s. 
  34. ^ a b Nb(I) and Ta(I) occur in CpNb(CO)4 and CpTa(CO)4, see Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils (1995). "Tantal". Lehrbuch der Anorganischen Chemie (in German) (101 ed.). Walter de Gruyter. p. 1430. ISBN 3-11-012641-9.  and King, R. Bruce (1969). Transition-Metal Organometallic Chemistry: An Introduction. Academic Press. p. 11. ISBN 0-32-315996-6. 
  35. ^ Pd(I) has been observed; see Crabtree, R. H. (2002). "CHEMISTRY: A New Oxidation State for Pd?". Science. 295 (5553): 288–289. doi:10.1126/science.1067921. 
  36. ^ Pd(III) has been observed; see Powers, D. C.; Ritter, T. (2011). "Palladium(III) in Synthesis and Catalysis" (PDF). Top. Organomet. Chem. Topics in Organometallic Chemistry. 35: 129–156. ISBN 978-3-642-17428-5. doi:10.1007/978-3-642-17429-2_6. Archived from the original on June 12, 2013. 
  37. ^ Pd(V) has been observed in dioxygenyl hexafluoropalladate; see Falconer, W. E.; Disalvo, F. J.; Edwards, A. J.; Griffiths, J. E.; Sunder, W. E.; Vasile, M. J. (1976). "Dioxygenyl hexafluoropalladate(V) O2+PdF6: A quinquevalent compound of palladium". Journal of Inorganic and Nuclear Chemistry. 28, Supplement 1: 59–60. doi:10.1016/0022-1902(76)80595-7. 
  38. ^ Pd(VI) complexes have been observed; see Chen, W.; Shimada, Shigeru; Tanaka, Masato (2002). "Synthesis and Structure of Formally Hexavalent Palladium Complexes". Science. 295 (5553): 308–310. Bibcode:2002Sci...295..308C. PMID 11786638. doi:10.1126/science.1067027. 
  39. ^ The Ag ion has been observed in metal ammonia solutions: see Tran, N. E.; Lagowski, J. J. (2001). "Metal Ammonia Solutions: Solutions Containing Argentide Ions.". Inorganic Chemistry. 40 (5): 1067–68. doi:10.1021/ic000333x. 
  40. ^ Ag(IV) has been observed in potassium hexafluoroargentate (K2AgF6) and caesium hexafluoroargentate (Cs2AgF6); see Riedel, Sebastian; Kaupp, Martin (2009). "The highest oxidation states of the transition metal elements" (PDF). Coordination Chemistry Reviews. Elsevier. 253 (5–6): 606–624. doi:10.1016/j.ccr.2008.07.014. [permanent dead link]
  41. ^ 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. ISBN 3-11-007511-3. 
  42. ^ In(–5) has been observed in La3InGe, see Guloy, A. M.; Corbett, J. D. (1996). "Synthesis, Structure, and Bonding of Two Lanthanum Indium Germanides with Novel Structures and Properties". Inorganic Chemistry. 35 (9): 2616–22. doi:10.1021/ic951378e. 
  43. ^ In(−2) has been observed in Na2In, see [6], p. 69.
  44. ^ Sn(−3) has been observed in [Sn2]6−, e.g. in (Ba2)4+(Mg4)8+Sn4−(Sn2)6−Sn2− (with square (Sn2−)n sheets), see Papoian, Garegin A.; Hoffmann, Roald (2000). "Hypervalent Bonding in One, Two, and Three Dimensions: Extending the Zintl–Klemm Concept to Nonclassical Electron-Rich Networks" (PDF). Angew. Chem. Int. Ed. 2000 (39): 2408–2448. doi:10.1002/1521-3773(20000717)39:14<2408::aid-anie2408>3.0.co;2-u. Retrieved 2015-02-23. 
  45. ^ Sn(I) and Sn(III) have been observed in organotin compounds
  46. ^ Sb(−2) has been observed in [Sb2]4−, e.g. in RbBa4[Sb2][Sb][O], see Boss, Michael; Petri, Denis; Pickhard, Frank; Zönnchen, Peter; Röhr, Caroline (2005). "Neue Barium-Antimonid-Oxide mit den Zintl-Ionen [Sb]3−, [Sb2]4− und 1[Sbn]n− / New Barium Antimonide Oxides containing Zintl Ions [Sb]3−, [Sb2]4− and 1[Sbn]n−". Zeitschrift für anorganische und allgemeine Chemie (in German). 631 (6–7): 1181–1190. doi:10.1002/zaac.200400546. Retrieved 2015-02-23. 
  47. ^ Sb(I) and Sb(II) have been observed in organoantimony compounds; for Sb(I), see Šimon, Petr; de Proft, Frank; Jambor, Roman; Růžička, Aleš; Dostál, Libor (2010). "Monomeric Organoantimony(I) and Organobismuth(I) Compounds Stabilized by an NCN Chelating Ligand: Syntheses and Structures". Angewandte Chemie International Edition. 49 (32): 5468–5471. PMID 20602393. doi:10.1002/anie.201002209. Retrieved 2015-02-23. 
  48. ^ Sb(IV) has been observed in [SbCl
    6
    ]2−
    , see Nobuyoshi Shinohara; Masaaki Ohsima (2000). "Production of Sb(IV) Chloro Complex by Flash Photolysis of the Corresponding Sb(III) and Sb(V) Complexes in CH3CN and CHCl3". Bulletin of the Chemical Society of Japan. 73 (7): 1599–1604. doi:10.1246/bcsj.73.1599. 
  49. ^ Te(I) has been observed in tellurium iodide (TeI), see "Tellurium: tellurium iodide". WebElements.com. Retrieved 2015-02-23. 
  50. ^ Te(III) has been observed in [Te(N(SiMe3)2)2]+, see Heinze, Thorsten; Roesky, Herbert W.; Pauer, Frank; Stalke, Dietmar; Sheldrick, George M. (1991). "Synthesis and Structure of the First Tellurium(III) Radical Cation". Angewandte Chemie International Edition. 30 (12): 1678. doi:10.1002/anie.199116771. Retrieved 2015-02-23. .
  51. ^ Te(V) is mentioned by Greenwood and Earnshaw, but they do not give any example of a Te(V) compound. What was long thought to be ditellurium decafluoride (Te2F10) is actually bis(pentafluorotelluryl) oxide, F5TeOTeF5: see Watkins, P. M. (1974). "Ditellurium decafluoride - A Continuing Myth". Journal of Chemical Education. 51 (9): 520–521. doi:10.1021/ed051p520.  However, Te(V) has been observed in H
    2
    TeO
    4
    , TeO
    3
    , HTeO2−
    4
    , and TeO3−
    4
    ; see Kläning, Ulrik K.; Sehested, K. (2001). "Tellurium(V). A Pulse Radiolysis Study". The Journal of Physical Chemistry A. 105 (27): 6637–45. doi:10.1021/jp010577i. 
  52. ^ 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. ISBN 0-486-65622-5. 
  53. ^ I(VI) has been observed in IO3, IO42−, H5IO6, H2IO52−, H4IO62−, and HIO53−; see Kläning, Ulrik K.; Sehested, Knud; Wolff, Thomas (1981). "Laser flash photolysis and pulse radiolysis of iodate and periodate in aqueous solution. Properties of iodine(VI)". J. Chem. Soc., Faraday Trans. 1. 77: 1707–18. doi:10.1039/F19817701707. 
  54. ^ Xe(I) has been reported in xenon hexafluoroplatinate and xenon hexafluororhodate (see Pauling, Linus (1988). General Chemistry (3rd ed.). Dover Publications, Inc. p. 250. ISBN 0-486-65622-5. ), however these compounds were later found to contain Xe(II).
  55. ^ Ba(I) has been observed in barium monofluoride (BaF); see P. Colarusso; Guo, B.; Zhang, K.-Q.; Bernath, P.F.; et al. (1995). "High-Resolution Fourier Transform Infrared Emission Spectrum of Barium Monofluoride" (PDF). J. Molecular Spectroscopy. 170: 59. Bibcode:1996JMoSp.175..158C. doi:10.1006/jmsp.1996.0019. Archived from the original (PDF) on 2005-03-10. 
  56. ^ La(I) has been observed in lanthanum monohydride (LaH); see Ram, R. S.; Bernath, P. F. (1996). "Fourier Transform Emission Spectroscopy of New Infrared Systems of LaH and LaD" (PDF). J. Molecular Spectroscopy. 104: 6444. doi:10.1063/1.471365. Archived from the original (PDF) on 2005-03-10. 
  57. ^ Pr(V) has been observed in [PrO2]+; see Zhang, Qingnan; Hu, Shu-Xian; Qu, Hui; Su, Jing; Wang, Guanjun; Lu, Jun-Bo; Chen, Mohua; Zhou, Mingfei; Li, Jun (2016-06-06). "Pentavalent Lanthanide Compounds: Formation and Characterization of Praseodymium(V) Oxides". Angewandte Chemie International Edition. 55 (24): 6896–6900. ISSN 1521-3773. PMID 27100273. doi:10.1002/anie.201602196. 
  58. ^ Nd(IV) has been observed in unstable solid state compounds; see Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN 0-12-352651-5 
  59. ^ a b c d e All the lanthanides (La–Lu) in the +2 oxidation state have been observed (except La, Gd, Lu) in dilute, solid solutions of dihalides of these elements in alkaline earth dihalides (see Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN 0-12-352651-5 ) and (except Pm) in organometallic molecular complexes, see Lanthanides Topple Assumptions and Meyer, G. (2014). "All the Lanthanides Do It and Even Uranium Does Oxidation State +2.". Angewandte Chemie International Edition. 53 (14): 3550–51. PMID 24616202. doi:10.1002/anie.201311325. . Additionally, all the lanthanides (La–Lu) form dihydrides (LnH2), dicarbides (LnC2), monosulfides (LnS), monoselenides (LnSe), and monotellurides (LnTe), but for most elements these compounds have Ln3+ ions with electrons delocalized into conduction bands, e. g. Ln3+(H)2(e).
  60. ^ Dy(IV) has been observed in unstable solid state compounds; see Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN 0-12-352651-5 
  61. ^ Hf(I) has been observed in hafnium monobromide (HfBr), see Marek, G.S.; Troyanov, S.I.; Tsirel'nikov, V.I. (1979). "Кристаллическое строение и термодинамические характеристики монобромидов циркония и гафния / Crystal structure and thermodynamic characteristics of monobromides of zirconium and hafnium". Журнал неорганической химии / Russian Journal of Inorganic Chemistry (in Russian). 24 (4): 890–893. 
  62. ^ 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 Chemistry. 454: 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 Chemistry. 21 (11): 3955–3960. doi:10.1021/ic00141a019. 
  63. ^ Ir(−3) has been observed in Ir(CO)33−; see Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1117. ISBN 0-08-037941-9. 
  64. ^ Ir(VII) has been observed in [(η2-O2)IrO2]+; see C&EN: Iridium dressed to the nines.
  65. ^ 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 Edition. 48 (42): 7879–7883. doi:10.1002/anie.200902733. 
  66. ^ 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". Nature. 514: 475–477. PMID 25341786. doi:10.1038/nature13795. 
  67. ^ Pt(−1) and Pt(−2) have been observed in the barium platinides Ba2Pt and BaPt, 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. PMID 16479284. doi:10.1039/b514631c. 
  68. ^ Pt(I) and Pt(III) have been observed in bimetallic and polymetallic species; see Kauffman, George B.; Thurner, Joseph J.; Zatko, David A. (1967). "Ammonium Hexachloroplatinate(IV)". Inorganic Syntheses. Inorganic Syntheses. 9: 182–185. ISBN 978-0-470-13240-1. doi:10.1002/9780470132401.ch51. 
  69. ^ Tl(−5) has been observed in Na23K9Tl15.3, see Dong, Z.-C.; Corbett, J. D. (1996). "Na23K9Tl15.3:  An Unusual Zintl Compound Containing Apparent Tl57−, Tl48−, Tl37−, and Tl5− Anions". Inorganic Chemistry. 35 (11): 3107–12. doi:10.1021/ic960014z. 
  70. ^ Tl(−1) has been observed in caesium thallide (CsTl); see King, R. B.; Schleyer, R. (2004). "Theory and concepts in main-group cluster chemistry". In Driess, M.; Nöth, H. Molecular clusters of the main group elements. Wiley-VCH, Chichester. p. 19. ISBN 978-3-527-61437-0. 
  71. ^ Tl(+2) has been observed in tetrakis(hypersilyl)dithallium ([(Me3Si)Si]2Tl—Tl[Si(SiMe3)]2), see Sonja Henkel; Dr. Karl Wilhelm Klinkhammer; Dr. Wolfgang Schwarz (1994). "Tetrakis(hypersilyl)dithallium(Tl—Tl): A Divalent Thallium Compound". Angew. Chem. Int. Ed. 33 (6): 681–683. doi:10.1002/anie.199406811. .
  72. ^ Pb(−2) has been observed in BaPb, see Ferro, Riccardo (2008). Nicholas C. Norman, ed. Intermetallic Chemistry. Elsevier. p. 505. ISBN 978-0-08-044099-6.  and Todorov, Iliya; Sevov, Slavi C. (2004). "Heavy-Metal Aromatic Rings: Cyclopentadienyl Anion Analogues Sn56− and Pb56− in the Zintl Phases Na8BaPb6, Na8BaSn6, and Na8EuSn6.". Inorganic Chemistry. 43 (20): 6490–94. doi:10.1021/ic000333x. 
  73. ^ Pb(+1) and Pb(+3) have been observed in organolead compounds, e.g. hexamethyldiplumbane Pb2(CH3)6; for Pb(I), see Siew-Peng Chia; Hong-Wei Xi; Yongxin Li; Kok Hwa Lim; Cheuk-Wai So (2013). "A Base-Stabilized Lead(I) Dimer and an Aromatic Plumbylidenide Anion". Angew. Chem. Int. Ed. 52 (24): 6298–6301. doi:10.1002/anie.201301954. .
  74. ^ Bi(−2) and Bi(−1) occur in Zintl phases, e.g. (Ca2+)22[Bi4]4−([Bi2]4−)4[Bi3−]8; see Ponou, Siméon (2006). "Germanides, Germanide-Tungstate Double Salts and Substitution Effects in Zintl Phases". Technische Universität München. Lehrstuhl für Anorganische Chemie mit Schwerpunkt Neue Materialien. p. 68. 
  75. ^ 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. ISBN 0-7514-0389-X. 
  76. ^ Bi(+2) has been observed in dibismuthines (R2Bi—BiR2), see Arthur J. Ashe III (1990). "Thermochromic Distibines and Dibismuthines". Advances in Organometallic Chemistry. 30: 77–97. doi:10.1016/S0065-3055(08)60499-2. 
  77. ^ Bi(IV) has been observed; see A. I. Aleksandrov, I. E. Makarov (1987). "Formation of Bi(II) and Bi(IV) in aqueous hydrochloric solutions of Bi(III)". Bulletin of the Academy of Sciences of the USSR, Division of chemical science. 36 (2): 217–220. doi:10.1007/BF00959349. 
  78. ^ Po(V) has been observed in dioxidopolonium(1+) (PoO+
    2
    ); see Thayer, John S. (2010). Relativistic Effects and the Chemistry of the Heavier Main Group Elements. p. 78. doi:10.1007/978-1-4020-9975-5_2. 
  79. ^ Rn(II) has been observed in radon difluoride (RnF2); see Stein, L. (1970). "Ionic Radon Solution". Science. 168 (3929): 362–4. Bibcode:1970Sci...168..362S. PMID 17809133. doi:10.1126/science.168.3929.362.  and Kenneth S. Pitzer (1975). "Fluorides of radon and element 118". J. Chem. Soc., Chem. Commun. (18): 760b – 761. doi:10.1039/C3975000760b. 
  80. ^ Rn(IV) is reported by Greenwood and Earnshaw, but is not known to exist; see Sykes, A. G. (1998). "Recent Advances in Noble-Gas Chemistry". Advances in Inorganic Chemistry. 46. Academic Press. pp. 91–93. ISBN 978-0-12-023646-6. Retrieved 22 November 2012. 
  81. ^ Rn(VI) is known in radon trioxide (RnO3); see Sykes, A. G. (1998). "Recent Advances in Noble-Gas Chemistry". Advances in Inorganic Chemistry. 46. Academic Press. pp. 91–93. ISBN 978-0-12-023646-6. Retrieved 22 November 2012. 
  82. ^ Th(I) is known in thorium(I) bromide (ThBr); see Wickleder, Mathias S.; Fourest, Blandine; Dorhout, Peter K. (2006). "Thorium". In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean. The Chemistry of the Actinide and Transactinide Elements (PDF). 3 (3rd ed.). Dordrecht, the Netherlands: Springer. pp. 52–160. doi:10.1007/1-4020-3598-5_3. Archived from the original (PDF) on 2016-03-07. 
  83. ^ Th(II) and Th(III) are observed in [ThII{η5-C5H3(SiMe3)2}3] and [ThIII{η5-C5H3(SiMe3)2}3], see Langeslay, Ryan R.; Fieser, Megan E.; Ziller, Joseph W.; Furche, Philip; Evans, William J. (2015). "Synthesis, structure, and reactivity of crystalline molecular complexes of the {[C5H3(SiMe3)2]3Th}1− anion containing thorium in the formal +2 oxidation state". Chem. Sci. 6: 517–521. doi:10.1039/C4SC03033H. Retrieved 16 July 2016. 
  84. ^ U(I) has been observed in uranium monofluoride (UF) and uranium monochloride (UCl), see Sykes, A. G. (1990). "Compounds of Thorium and Uranium". Advances in Inorganic Chemistry. 34. Academic Press. pp. 87–88. ISBN 0-12-023634-6. Retrieved 22 March 2015. 
  85. ^ U(II) has been observed in [K(2.2.2-Cryptand)][(C5H4SiMe3)3U], see MacDonald, Matthew R.; Fieser, Megan E.; Bates, Jefferson E.; Ziller, Joseph W.; Furche, Filipp; Evans, William J. (2013). "Identification of the +2 Oxidation State for Uranium in a Crystalline Molecular Complex, [K(2.2.2-Cryptand)][(C5H4SiMe3)3U]". J. Am. Chem. Soc. 135 (36): 13310–13313. doi:10.1021/ja406791t. 
  86. ^ Np(II) has been observed, see Dutkiewicz, Michał S.; Apostolidis, Christos; Walter, Olaf; Arnold, Polly L (2017). "Reduction chemistry of neptunium cyclopentadienide complexes: from structure to understanding". Chem. Sci. 8: 2553–2561. doi:10.1039/C7SC00034K. 
  87. ^ Pu(II) has been observed in {Pu[C5H3(SiMe3)2]3}−; see Windorff, Cory J.; Chen, Guo P; Cross, Justin N; Evans, William J.; Furche, Filipp; Gaunt, Andrew J.; Janicke, Michael T.; Kozimor, Stosh A.; Scott, Brian L. (2017). "Identification of the Formal +2 Oxidation State of Plutonium: Synthesis and Characterization of {PuII[C5H3(SiMe3)2]3}−". J. Am. Chem. Soc. 139 (11): 3970–3973. doi:10.1021/jacs.7b00706. 
  88. ^ 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. ISBN 0-08-037941-9. 
  89. ^ 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. 
  90. ^ Cm(VIII) has been reported to possibly occur 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.  However, new experiments seem to indicate its nonexistence: Zaitsevskii, Andréi; Schwarz, W H Eugen (April 2014). "Structures and stability of AnO4 isomers, An = Pu, Am, and Cm: a relativistic density functional study.". Physical Chemistry Chemical Physics. 2014 (16): 8997–9001. doi:10.1039/c4cp00235k. 
  91. ^ Es(IV) is known in einsteinium(IV) fluoride (EsF4); see Kleinschmidt, P (1994). "Thermochemistry of the actinides". Journal of Alloys and Compounds. 213–214: 169–172. doi:10.1016/0925-8388(94)90898-2. 
  92. ^ Db(V) has been observed in dubnium pentachloride (DbCl5); see H. W. Gäggeler (2007). "Gas Phase Chemistry of Superheavy Elements" (PDF). Paul Scherrer Institute. pp. 26–28. Archived from the original (PDF) on 2012-02-20. 
  93. ^ Sg(VI) has been observed in seaborgium oxide hydroxide (SgO2(OH)2); see Huebener; Taut, S.; Vahle, A.; Dressler, R.; Eichler, B.; Gäggeler, H. W.; Jost, D.T.; Piguet, D.; et al. (2001). "Physico-chemical characterization of seaborgium as oxide hydroxide" (PDF). Radiochim. Acta. 89 (11–12_2001): 737–741. doi:10.1524/ract.2001.89.11-12.737. Archived from the original (PDF) on 2014-10-25. 
  94. ^ Bh(VII) has been observed in bohrium oxychloride (BhO3Cl); see "Gas chemical investigation of bohrium (Bh, element 107)" Archived 2008-02-28 at the Wayback Machine., Eichler et al., GSI Annual Report 2000. Retrieved on 2008-02-29
  95. ^ Hs(VIII) has been observed in hassium tetroxide (HsO4); see "Chemistry of Hassium" (PDF). Gesellschaft für Schwerionenforschung mbH. 2002. Retrieved 2007-01-31. 
  96. ^ Cn(II) has been observed in copernicium selenide (CnSe); see Paul Scherrer Institute (2015). "Annual Report 2015: Laboratory of Radiochemistry and Environmental Chemistry" (PDF). Paul Scherrer Institute. p. 3. 
  97. ^ Langmuir, Irving (1919). "The arrangement of electrons in atoms and molecules". J. Am. Chem. Soc. 41 (6): 868–934. doi:10.1021/ja02227a002. 

See also[edit]