Editing Nobelium (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=2014-08-15 |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]], nobelium is located to the right of the actinide [[mendelevium]], to the left of the actinide [[lawrencium]], and below the lanthanide [[ytterbium]]. Nobelium metal has not yet been prepared in bulk quantities, and bulk preparation is currently impossible.<ref name="Silva1639">{{harvnb|Silva|2011|p=1639}}</ref> Nevertheless, a number of predictions and some preliminary experimental results have been done regarding its properties.<ref name="Silva1639" />

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">{{harvnb|Silva|2011|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>13</sup>6d<sup>1</sup>7s<sup>2</sup> configuration over the [Rn]5f<sup>14</sup>7s<sup>2</sup> configuration for nobelium 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, although for nobelium this prediction has not yet been confirmed.<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: an effect of this is that nobelium is predominantly divalent instead of trivalent, unlike all the other lanthanides and actinides.<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=978-0-8412-0568-0 |last=Hulet |first=E. Kenneth |editor-last=Edelstein |editor-first=Norman M. |chapter=Chapter 12. Chemistry of the Heaviest Actinides: Fermium, Mendelevium, Nobelium, and Lawrencium |series=ACS Symposium Series |chapter-url-access=registration |chapter-url=https://archive.org/details/lanthanideactini0000unse |url=https://archive.org/details/lanthanideactini0000unse/page/239 }}</ref> In 1986, nobelium metal was estimated to have an [[enthalpy of sublimation]] between 126&nbsp;kJ/mol, a value close to the values for einsteinium, fermium, and mendelevium and supporting the theory that nobelium would form a divalent metal.<ref name="Silva1639" /> Like the other divalent late actinides (except the once again trivalent lawrencium), metallic nobelium should assume a [[face-centered cubic]] crystal structure.<ref name="density" /> Divalent nobelium metal should have a [[metallic radius]] of around 197&nbsp;[[picometer|pm]].<ref name="Silva1639" /> Nobelium's melting point has been predicted to be 800&nbsp;°C, the same value as that estimated for the neighboring element mendelevium.<ref>{{cite book |ref=Haynes |editor-last=Haynes |editor-first=William M. |date=2011 |title= CRC Handbook of Chemistry and Physics |edition=92nd |publisher=CRC Press |isbn=978-1-4398-5511-9 |pages=4.121–4.123 }}</ref> Its density is predicted to be around 9.9&nbsp;±&nbsp;0.4&nbsp;g/cm<sup>3</sup>.<ref name="density" />