Editing Fermium (section)

==Chemistry==
[[File:Fermium-Ytterbium Alloy.jpg|thumb|A fermium-[[ytterbium]] alloy used for measuring the [[enthalpy of sublimation]] of fermium metal<ref>{{Cite journal|last1=Haire|first1=Richard G.|last2=Gibson|first2=John K.|title=The enthalpy of sublimation and thermodynamic functions of fermium|url=https://pubs.aip.org/aip/jcp/article-abstract/91/11/7085/95919/The-enthalpy-of-sublimation-and-thermodynamic|journal=The Journal of Chemical Physics|date=1989 |language=en|volume=91|issue=11 |pages=7085–7096|doi=10.1063/1.457326|bibcode=1989JChPh..91.7085H }}</ref>]]

The chemistry of fermium has only been studied in solution using tracer techniques, and no solid compounds have been prepared. Under normal conditions, fermium exists in solution as the Fm<sup>3+</sup> ion, which has a [[hydration number]] of 16.9 and an [[acid dissociation constant]] of 1.6{{e|−4}} (p''K''{{sub|a}}&nbsp;= 3.8).<ref>{{cite journal|last1 = Lundqvist|first1 = Robert|last2 = Hulet|first2 = E. K.|last3 = Baisden|first3 = T. A.|date = 1981|last4 = Näsäkkälä|first4 = Elina|last5 = Wahlberg|first5 = Olof|title = Electromigration Method in Tracer Studies of Complex Chemistry. II. Hydrated Radii and Hydration Numbers of Trivalent Actinides|journal = Acta Chemica Scandinavica A|volume = 35|pages = 653–661|doi = 10.3891/acta.chem.scand.35a-0653|doi-access = free}}</ref><ref>{{cite journal|last1 = Hussonnois|first1 = H.|last2 = Hubert|first2 = S.|last3 = Aubin|first3 = L.|last4 = Guillaumont|first4 = R.|author-link4=Robert Guillaumont|last5 = Boussieres|first5 = G.|date = 1972|journal = Radiochem. Radioanal. Lett.|volume = 10|pages = 231–238}}</ref> Fm{{sup|3+}} forms complexes with a wide variety of organic ligands with [[HSAB theory|hard]] donor atoms such as oxygen, and these complexes are usually more stable than those of the preceding actinides.<ref name="Silva" /> It also forms anionic complexes with ligands such as [[chloride]] or [[nitrate]] and, again, these complexes appear to be more stable than those formed by [[einsteinium]] or [[californium]].<ref>{{cite journal|last1 = Thompson|first1 = S. G.|last2 = Harvey|first2 = B. G.|last3 = Choppin|first3 = G. R.|last4 = Seaborg|first4 = G. T.|author-link4 = Glenn T. Seaborg|date = 1954|title = Chemical Properties of Elements 99 and 100|journal = J. Am. Chem. Soc.|volume = 76|issue = 24|pages = 6229–6236|doi = 10.1021/ja01653a004|url = https://digital.library.unt.edu/ark:/67531/metadc1023183/|bibcode = 1954JAChS..76.6229T}}</ref> It is believed that the bonding in the complexes of the later actinides is mostly [[Ionic bond|ionic]] in character: the Fm{{sup|3+}} ion is expected to be smaller than the preceding An{{sup|3+}} ions because of the higher [[effective nuclear charge]] of fermium, and hence fermium would be expected to form shorter and stronger metal–ligand bonds.<ref name="Silva" />

Fermium(III) can be fairly easily reduced to fermium(II),<ref>{{cite journal|last = Malý|first = Jaromír|date = 1967|title = The amalgamation behaviour of heavy elements 1. Observation of anomalous preference in formation of amalgams of californium, einsteinium, and fermium|journal = Inorg. Nucl. Chem. Lett.|volume = 3|issue = 9|pages = 373–381|doi = 10.1016/0020-1650(67)80046-1}}</ref> for example with [[samarium(II) chloride]], with which fermium(II) coprecipitates.<ref>{{cite journal|last1 = Mikheev|first1 = N. B.|last2 = Spitsyn|first2 = V. I.|last3 = Kamenskaya|first3 = A. N.|last4 = Gvozdec|first4 = B. A.|last5 = Druin|first5 = V. A.|last6 = Rumer|first6 = I. A.|last7 = Dyachkova|first7 = R. A.|last8 = Rozenkevitch|first8 = N. A.|last9 = Auerman|first9 = L. N.|date = 1972|title = Reduction of fermium to divalent state in chloride aqueous ethanolic solutions|journal = Inorg. Nucl. Chem. Lett.|volume = 8|issue = 11|pages = 929–936|doi = 10.1016/0020-1650(72)80202-2}}</ref><ref>{{cite journal|last1 = Hulet|first1 = E. K.|last2 = Lougheed|first2 = R. W.|last3 = Baisden|first3 = P. A.|last4 = Landrum|first4 = J. H.|last5 = Wild|first5 = J. F.|last6 = Lundqvist|first6 = R. F.|date = 1979|title = Non-observance of monovalent Md|journal = J. Inorg. Nucl. Chem.|volume = 41|issue = 12|pages = 1743–1747|doi = 10.1016/0022-1902(79)80116-5}}</ref> In the precipitate, the compound fermium(II) chloride (FmCl{{sub|2}}) was produced, though it was not purified or studied in isolation.<ref>{{cite book |title=Dictionary of Inorganic Compounds |page=2873 |date=1992 |volume=3 |edition=1 |publisher=Chapman & Hall |isbn=0412301202}}</ref> The [[electrode potential]] has been estimated to be similar to that of the [[ytterbium]](III)/(II) couple, or about −1.15&nbsp;V with respect to the [[standard hydrogen electrode]],<ref>{{cite journal|last1 = Mikheev|first1 = N. B.|last2 = Spitsyn|first2 = V. I.|last3 = Kamenskaya|first3 = A. N.|last4 = Konovalova|first4 = N. A.|last5 = Rumer|first5 = I. A.|last6 = Auerman|first6 = L. N.|last7 = Podorozhnyi|first7 = A. M.|date = 1977|title = Determination of oxidation potential of the pair Fm{{sup|2+}}/Fm{{sup|3+}}|journal = Inorg. Nucl. Chem. Lett.|volume = 13|issue = 12|pages = 651–656|doi = 10.1016/0020-1650(77)80074-3}}</ref> a value which agrees with theoretical calculations.<ref>{{cite journal|last = Nugent|first = L. J.|date = 1975|journal = MTP Int. Rev. Sci.: Inorg. Chem. |volume = 7|pages = 195–219}}</ref> The Fm{{sup|2+}}/Fm{{sup|0}} couple has an electrode potential of −2.37(10)&nbsp;V based on [[Polarography|polarographic]] measurements.<ref>{{cite journal|last1 = Samhoun|first1 = K.|last2 = David|first2 = F.|last3 = Hahn|first3 = R. L.|last4 = O'Kelley|first4 = G. D.|last5 = Tarrant|first5 = J. R.|last6 = Hobart|first6 = D. E.|date = 1979|title = Electrochemical study of mendelevium in aqueous solution: No evidence for monovalent ions|journal = J. Inorg. Nucl. Chem.| volume = 41|issue = 12|pages = 1749–1754|doi = 10.1016/0022-1902(79)80117-7}}</ref>