Editing Mendelevium (section)

===Physical===
[[File:Fblock fd promotion energy.png|thumb|upright=1.6|right|Energy required to promote an f electron to the d subshell for the f-block [[lanthanides]] and [[actinides]]. Above around 210&nbsp;kJ/mol, this energy is too high to be provided for by the greater [[crystal energy]] of the trivalent state and thus [[einsteinium]], [[fermium]], and mendelevium form divalent metals like the lanthanides [[europium]] and [[ytterbium]]. ([[Nobelium]] is also expected to form a divalent metal, but this has not yet been confirmed.)<ref>{{cite book|first = Richard G.|last = Haire|ref = Haire|contribution = Einsteinium|title = The Chemistry of the Actinide and Transactinide Elements|editor1-first = Lester R.|editor1-last = Morss|editor2-first = Norman M.|editor2-last = Edelstein|editor3-first = Jean|editor3-last = Fuger|edition = 3rd|date = 2006|volume = 3|publisher = Springer|location = Dordrecht, the Netherlands|pages = 1577–1620|url = http://radchem.nevada.edu/classes/rdch710/files/einsteinium.pdf|doi = 10.1007/1-4020-3598-5_12|isbn = 978-1-4020-3555-5|access-date = 2014-08-04|archive-date = 2010-07-17|archive-url = https://web.archive.org/web/20100717154427/http://radchem.nevada.edu/classes/rdch710/files/einsteinium.pdf|url-status = dead}}</ref>]]
In the [[periodic table]], mendelevium is located to the right of the actinide [[fermium]], to the left of the actinide [[nobelium]], and below the lanthanide [[thulium]]. Mendelevium metal has not yet been prepared in bulk quantities, and bulk preparation is currently impossible.<ref name="Silva16345">Silva, pp. 1634–5</ref> Nevertheless, a number of predictions and some preliminary experimental results have been done regarding its properties.<ref name="Silva16345" />

The lanthanides and actinides, in the metallic state, can exist as either divalent (such as [[europium]] and [[ytterbium]]) or trivalent (most other lanthanides) metals. The former have f<sup>''n''</sup>s<sup>2</sup> configurations, whereas the latter have f<sup>''n''−1</sup>d<sup>1</sup>s<sup>2</sup> configurations. In 1975, Johansson and Rosengren examined the measured and predicted values for the [[cohesive energy|cohesive energies]] ([[enthalpy|enthalpies]] of crystallization) of the metallic [[lanthanide]]s and [[actinide]]s, both as divalent and trivalent metals.<ref name="Silva16268">Silva, pp. 1626–8</ref><ref>{{cite journal|doi=10.1103/PhysRevB.11.2836|title=Generalized phase diagram for the rare-earth elements: Calculations and correlations of bulk properties|date=1975|last1=Johansson|first1=Börje|last2=Rosengren|first2=Anders|journal=Physical Review B|volume=11|pages=2836–2857|bibcode = 1975PhRvB..11.2836J|issue=8 }}</ref> The conclusion was that the increased binding energy of the [Rn]5f<sup>12</sup>6d<sup>1</sup>7s<sup>2</sup> configuration over the [Rn]5f<sup>13</sup>7s<sup>2</sup> configuration for mendelevium was not enough to compensate for the energy needed to promote one 5f electron to 6d, as is true also for the very late actinides: thus [[einsteinium]], [[fermium]], mendelevium, and [[nobelium]] were expected to be divalent metals.<ref name="Silva16268" /> The increasing predominance of the divalent state well before the actinide series concludes is attributed to the [[relativistic quantum chemistry|relativistic]] stabilization of the 5f electrons, which increases with increasing atomic number.<ref>{{cite book|doi=10.1021/bk-1980-0131.ch012|title=Lanthanide and Actinide Chemistry and Spectroscopy|volume=131|pages=[https://archive.org/details/lanthanideactini0000unse/page/239 239–263]|date=1980|isbn=9780841205680|author=Hulet, E. K.|editor=Edelstein, Norman M.|chapter=Chapter 12. Chemistry of the Heaviest Actinides: Fermium, Mendelevium, Nobelium, and Lawrencium|series=ACS Symposium Series|chapter-url=https://archive.org/details/lanthanideactini0000unse|url=https://archive.org/details/lanthanideactini0000unse/page/239}}</ref> [[Thermochromatography|Thermochromatographic]] studies with trace quantities of mendelevium by Zvara and Hübener from 1976 to 1982 confirmed this prediction.<ref name="Silva16345" /> In 1990, Haire and Gibson estimated mendelevium metal to have an [[enthalpy of sublimation]] between 134 and 142&nbsp;kJ/mol.<ref name="Silva16345" /> Divalent mendelevium metal should have a [[metallic radius]] of around {{val|194|10|u=[[picometer|pm]]}}.<ref name="Silva16345" /> Like the other divalent late actinides (except the once again trivalent [[lawrencium]]), metallic mendelevium should assume a [[face-centered cubic]] crystal structure.<ref name="density" /> Mendelevium's melting point has been estimated at 800&nbsp;°C, the same value as that predicted for the neighboring element nobelium.<ref>{{cite book|ref=Haynes|editor=Haynes, William M.|date=2011|title= CRC Handbook of Chemistry and Physics |edition=92nd|publisher= CRC Press|isbn=978-1439855119|pages=4.121–4.123}}</ref> Its density is predicted to be around {{val|10.3|0.7|u=g/cm<sup>3</sup>}}.<ref name="density" />