Editing Roentgenium (section)

==Predicted properties==
Other than nuclear properties, no properties of roentgenium or its compounds have been measured; this is due to its extremely limited and expensive production<ref name="Superheavy element Bloomberg"/> and the fact that roentgenium (and its parents) decays very quickly. Properties of roentgenium metal remain unknown and only predictions are available.

===Chemical===
Roentgenium is the ninth member of the 6d series of [[transition metals]].<ref name="DoiX">{{cite journal|doi=10.1595/147106708X297486|title=The Periodic Table and the Platinum Group Metals|date=2008|last1=Griffith|first1=W. P.|journal=Platinum Metals Review|volume=52|issue=2|pages=114–119|doi-access=free}}</ref> Calculations on its [[ionization potential]]s and [[atomic radius|atomic]] and [[ionic radius|ionic radii]] are similar to that of its lighter homologue [[gold]], thus implying that roentgenium's basic properties will resemble those of the other [[group 11 element]]s, [[copper]], [[silver]], and gold; however, it is also predicted to show several differences from its lighter homologues.<ref name="Haire" />

Roentgenium is predicted to be a [[noble metal]]. The [[standard electrode potential]] of 1.9&nbsp;V for the Rg<sup>3+</sup>/Rg couple is greater than that of 1.5&nbsp;V for the Au<sup>3+</sup>/Au couple. Roentgenium's predicted first ionisation energy of 1020&nbsp;kJ/mol almost matches that of the [[noble gas]] [[radon]] at 1037&nbsp;kJ/mol.<ref name="Haire" /> Its predicted second ionization energy, 2070&nbsp;kJ/mol, is almost the same as that of silver. Based on the most stable oxidation states of the lighter group 11 elements, roentgenium is predicted to show stable +5 and +3 oxidation states, with a less stable +1 state. The +3 state is predicted to be the most stable. Roentgenium(III) is expected to be of comparable reactivity to gold(III), but should be more stable and form a larger variety of compounds. Gold also forms a somewhat stable −1 state due to relativistic effects, and it has been suggested roentgenium may do so as well:<ref name="Haire" /> nevertheless, the [[electron affinity]] of roentgenium is expected to be around {{convert|1.6|eVpar|abbr=on|lk=on}}, significantly lower than gold's value of {{convert|2.3|eVpar|abbr=on}}, so roentgenides may not be stable or even possible.{{Fricke1975}}
[[File:Electron_shell_111_roentgenium.png|thumb|Diagram of a roentgenium atom with [[electron shells]].]]
The 6d orbitals are destabilized by [[relativistic quantum chemistry|relativistic effects]] and [[spin–orbit interaction]]s near the end of the fourth transition metal series, thus making the high oxidation state roentgenium(V) more stable than its lighter homologue gold(V) (known only in [[gold pentafluoride]], Au<sub>2</sub>F<sub>10</sub>) as the 6d electrons participate in bonding to a greater extent. The spin-orbit interactions stabilize molecular roentgenium compounds with more bonding 6d electrons; for example, {{chem|RgF|6|-}} is expected to be more stable than {{chem|RgF|4|-}}, which is expected to be more stable than {{chem|RgF|2|-}}.<ref name="Haire" /> The stability of {{chem|RgF|6|-}} is homologous to that of {{chem|AuF|6|-}}; the silver analogue {{chem|AgF|6|-}} is unknown and is expected to be only marginally stable to decomposition to {{chem|AgF|4|-}} and F<sub>2</sub>. Moreover, Rg<sub>2</sub>F<sub>10</sub> is expected to be stable to decomposition, exactly analogous to the Au<sub>2</sub>F<sub>10</sub>, whereas Ag<sub>2</sub>F<sub>10</sub> should be unstable to decomposition to Ag<sub>2</sub>F<sub>6</sub> and F<sub>2</sub>. [[Gold heptafluoride]], AuF<sub>7</sub>, is known as a gold(V) difluorine complex AuF<sub>5</sub>·F<sub>2</sub>, which is lower in energy than a true gold(VII) heptafluoride would be; RgF<sub>7</sub> is instead calculated to be more stable as a true roentgenium(VII) heptafluoride, although it would be somewhat unstable, its decomposition to Rg<sub>2</sub>F<sub>10</sub> and F<sub>2</sub> releasing a small amount of energy at room temperature.<ref name=hepta>{{cite journal |last1=Conradie |first1=Jeanet |last2=Ghosh |first2=Abhik |date=15 June 2019 |title=Theoretical Search for the Highest Valence States of the Coinage Metals: Roentgenium Heptafluoride May Exist |journal=Inorganic Chemistry |volume=2019 |issue=58 |pages=8735–8738 |doi=10.1021/acs.inorgchem.9b01139|pmid=31203606 |s2cid=189944098 }}</ref> Roentgenium(I) is expected to be difficult to obtain.<ref name="Haire" /><ref>{{cite journal|last1=Seth |first1=M. |last2=Cooke |first2=F. |last3=Schwerdtfeger |first3=P. |last4=Heully |first4=J.-L. |last5=Pelissier |first5=M. |date=1998 |journal=J. Chem. Phys. |volume=109 |pages=3935–43 |doi=10.1063/1.476993 |title=The chemistry of the superheavy elements. II. The stability of high oxidation states in group 11 elements: Relativistic coupled cluster calculations for the di-, tetra- and hexafluoro metallates of Cu, Ag, Au, and element 111 |issue=10|bibcode = 1998JChPh.109.3935S|s2cid=54803557 |hdl=2292/5208 |hdl-access=free }}</ref><ref>{{cite journal |last1=Seth |first1=M. |last2=Faegri |first2=K. |last3=Schwerdtfeger |first3=P. |date=1998 |journal=Angew. Chem. Int. Ed. Engl. |volume=37 |pages=2493–6 |doi=10.1002/(SICI)1521-3773(19981002)37:18<2493::AID-ANIE2493>3.0.CO;2-F |title=The Stability of the Oxidation State +4 in Group 14 Compounds from Carbon to Element 114 |issue=18|pmid=29711350 }}</ref> Gold readily forms the [[cyanide]] [[coordination complex|complex]] {{chem|Au(CN)|2|-}}, which is used in its extraction from ore through the process of [[gold cyanidation]]; roentgenium is expected to follow suit and form {{chem|Rg(CN)|2|-}}.<ref>{{cite journal |last1=Demissie |first1=Taye B. |last2=Ruud |first2=Kenneth |date=25 February 2017 |title=Darmstadtium, roentgenium, and copernicium form strong bonds with cyanide |journal=International Journal of Quantum Chemistry |volume=2017 |pages=e25393 |doi=10.1002/qua.25393 |url=https://munin.uit.no/bitstream/10037/13632/4/article.pdf |hdl=10037/13632 |hdl-access=free |access-date=August 29, 2019 |archive-date=October 9, 2022 |archive-url=https://ghostarchive.org/archive/20221009/https://munin.uit.no/bitstream/10037/13632/4/article.pdf |url-status=live }}</ref>

The probable chemistry of roentgenium has received more interest than that of the two previous elements, [[meitnerium]] and [[darmstadtium]], as the valence s-[[Electron shell#Subshells|subshells]] of the group 11 elements are expected to be relativistically contracted most strongly at roentgenium.<ref name="Haire" /> Calculations on the molecular compound Rg[[hydrogen|H]] show that relativistic effects double the strength of the roentgenium–hydrogen bond, even though spin–orbit interactions also weaken it by {{convert|0.7|eVpar|abbr=on}}. The compounds [[gold|Au]]X and RgX, where X = [[fluorine|F]], [[chlorine|Cl]], [[bromine|Br]], [[oxygen|O]], Au, or Rg, were also studied.<ref name="Haire" /><ref>{{cite journal|last1=Liu |first1=W. |last2=van Wüllen |first2=C. |date=1999 |journal=J. Chem. Phys. |volume=110 |pages=3730–5 |doi=10.1063/1.478237 |title=Spectroscopic constants of gold and eka-gold (element 111) diatomic compounds: The importance of spin–orbit coupling |issue=8|bibcode = 1999JChPh.110.3730L}}</ref> Rg<sup>+</sup> is predicted to be the [[HSAB theory|softest]] metal ion, even softer than Au<sup>+</sup>, although there is disagreement on whether it would behave as an [[acid]] or a [[base (chemistry)|base]].<ref name="Thayer">{{cite book |last1=Thayer |first1=John S. |title=Relativistic Methods for Chemists |chapter=Relativistic Effects and the Chemistry of the Heavier Main Group Elements |date=2010 |page=82 |doi=10.1007/978-1-4020-9975-5_2 |volume=10 |isbn=978-1-4020-9974-8 |series=Challenges and Advances in Computational Chemistry and Physics }}</ref><ref name="Hancock">{{cite journal |last1=Hancock |first1=Robert D. |last2=Bartolotti |first2=Libero J. |last3=Kaltsoyannis |first3=Nikolas |date=24 November 2006 |title=Density Functional Theory-Based Prediction of Some Aqueous-Phase Chemistry of Superheavy Element 111. Roentgenium(I) Is the 'Softest' Metal Ion |journal=Inorg. Chem. |volume=45 |issue=26 |pages=10780–5 |doi=10.1021/ic061282s|pmid=17173436 }}</ref> In aqueous solution, Rg<sup>+</sup> would form the [[aqua ion]] [Rg(H<sub>2</sub>O)<sub>2</sub>]<sup>+</sup>, with an Rg–O bond distance of 207.1&nbsp;[[picometer|pm]]. It is also expected to form Rg(I) complexes with [[ammonia]], [[phosphine]], and [[hydrogen sulfide]].<ref name="Hancock" />

===Physical and atomic===
Roentgenium is expected to be a solid under normal conditions and to crystallize in the [[body-centered cubic]] structure, unlike its lighter [[congener (chemistry)|congeners]] which crystallize in the [[face-centered cubic]] structure, due to its being expected to have different electron charge densities from them.<ref name="bcc" /> It should be a very heavy metal with a [[density]] of around 22–24&nbsp;g/cm<sup>3</sup>; in comparison, the densest known element that has had its density measured, [[osmium]], has a density of 22.61&nbsp;g/cm<sup>3</sup>.<ref name="density" /><ref name="kratz" /> The atomic radius of roentgenium is expected to be around 114&nbsp;pm.<ref name="Darleane"/>