Hassium

Hassium is a synthetic chemical element; it has symbol Hs and atomic number 108. It is highly radioactive: its most stable known isotopes have half-lives of about ten seconds.{{efn|name="most stable isotope"}} One of its isotopes, {{sup|270}}Hs, has magic numbers of protons and neutrons for deformed nuclei, giving it greater stability against spontaneous fission. Hassium is a superheavy element; it has been produced in a laboratory in very small quantities by fusing heavy nuclei with lighter ones. Natural occurrences of hassium have been hypothesized but never found.

In the periodic table, hassium is a transactinide element, a member of period 7 and group 8; it is thus the sixth member of the 6d series of transition metals. Chemistry experiments have confirmed that hassium behaves as the heavier homologue to osmium, reacting readily with oxygen to form a volatile tetroxide. The chemical properties of hassium have been only partly characterized, but they compare well with the chemistry of the other group 8 elements.

The main innovation that led to the discovery of hassium was cold fusion, where the fused nuclei do not differ by mass as much as in earlier techniques. It relied on greater stability of target nuclei, which in turn decreased excitation energy. This decreased the number of neutrons ejected during synthesis, creating heavier, more stable resulting nuclei. The technique was first tested at Joint Institute for Nuclear Research (JINR) in Dubna, Moscow Oblast, Russian SFSR, Soviet Union, in 1974. JINR used this technique to attempt synthesis of element 108 in 1978, in 1983, and in 1984; the latter experiment resulted in a claim that element 108 had been produced. Later in 1984, a synthesis claim followed from the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Hesse, West Germany. The 1993 report by the Transfermium Working Group, formed by the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP), concluded that the report from Darmstadt was conclusive on its own whereas that from Dubna was not, and major credit was assigned to the German scientists. GSI formally announced they wished to name the element hassium after the German state of Hesse (Hassia in Latin), home to the facility in 1992; this name was accepted as final in 1997.

Introduction to the heaviest elements

Discovery

{{See also|Discovery of the chemical elements|Timeline of chemical element discoveries}}

File:Apparatus for creation of superheavy elements en.svg in JINR. The trajectory within the detector and the beam focusing apparatus changes because of a dipole magnet in the former and quadrupole magnets in the latter.{{Cite journal|last1=Aksenov|first1=N. V.|last2=Steinegger|first2=P.|last3=Abdullin|first3=F. Sh.|last4=Albin|first4=Yury V.|last5=Bozhikov|first5=Gospodin A.|last6=Chepigin|first6=Viktor I. |last7=Eichler|first7=Robert|last8=Lebedev|first8=Vyacheslav Ya.|last9=Madumarov|first9=Alexander Sh.|last10=Malyshev|first10=Oleg N.|last11=Petrushkin|first11=Oleg V.|display-authors=3|date=2017|title=On the volatility of nihonium (Nh, Z = 113)|journal=The European Physical Journal A|volume=53|issue=7|pages=158|doi=10.1140/epja/i2017-12348-8|bibcode=2017EPJA...53..158A|s2cid=125849923|issn=1434-6001}}]]

= Cold fusion =

Nuclear reactions used in the 1960s resulted in high excitation energies that required expulsion of four or five neutrons; these reactions used targets made of elements with high atomic numbers to maximize the size difference between the two nuclei in a reaction. While this increased the chance of fusion due to the lower electrostatic repulsion between target and projectile, the formed compound nuclei often broke apart and did not survive to form a new element. Moreover, fusion inevitably produces neutron-poor nuclei, as heavier elements need more neutrons per proton for stability;{{efn|Generally, heavier nuclei require more neutrons because as the number of protons increases, so does electrostatic repulsion between them. This repulsion is balanced by the binding energy generated by the strong interaction between quarks within nucleons; it is enough to hold the quarks together in a nucleon together and some of it is left for binding of different nucleons. The more nucleons in a nucleus, the more energy there is for binding the nucleons (greater total binding energy does not necessarily mean greater binding energy per nucleon).{{Cite web |date=2019 |url=https://inchemistry.acs.org/content/inchemistry/en/atomic-news/modern-alchemy-creating-superheavy-elements.html |last=Poole-Sawyer |first=J. |title=Modern Alchemy: Creating Superheavy Elements |website=inChemistry |publisher=American Chemical Society |access-date=2020-01-27 |archive-date=27 January 2020 |archive-url=https://web.archive.org/web/20200127134511/https://inchemistry.acs.org/content/inchemistry/en/atomic-news/modern-alchemy-creating-superheavy-elements.html |url-status=live }} However, having too many neutrons per proton, while decreasing electrostatic repulsion per nucleon, results in beta decay.{{Cite web|title=Beta Decay|url=https://www2.lbl.gov/abc/wallchart/chapters/03/2.html|access-date=2020-08-28|work=Guide to the Nuclear Wall Chart|publisher=Lawrence Berkeley National Laboratory|archive-date=16 December 2017|archive-url=https://web.archive.org/web/20171216223958/http://www2.lbl.gov/abc/wallchart/chapters/03/2.html|url-status=live}}}} therefore, the necessary ejection of neutrons results in final products that are typically shorter-lived. As such, light beams (six to ten protons) allowed synthesis of elements only up to 106.{{Cite journal|last=Oganessian|first=Yu.|date=2012|title=Nuclei in the "Island of Stability" of Superheavy Elements|journal=Journal of Physics: Conference Series|volume=337|issue=1|pages=012005-1–012005-6|doi=10.1088/1742-6596/337/1/012005|bibcode=2012JPhCS.337a2005O|issn=1742-6596|doi-access=free}}

To advance to heavier elements, Soviet physicist Yuri Oganessian at Joint Institute for Nuclear Research (JINR) in Dubna, Moscow Oblast, Russian SFSR, Soviet Union, proposed a different mechanism, in which the bombarded nucleus would be lead-208, which has magic numbers of protons and neutrons, or another nucleus close to it.{{Cite journal |last=Oganessian|first=Yu. Ts. |date=2004|title=Superheavy elements|journal=Pure and Applied Chemistry |volume=76|issue=9|pages=1717–1718|doi=10.1351/pac200476091715|issn=1365-3075|doi-access=free}} Each proton and neutron has a fixed rest energy; those of all protons are equal and so are those of all neutrons. In a nucleus, some of this energy is diverted to binding protons and neutrons; if a nucleus has a magic number of protons and/or neutrons, then even more of its rest energy is diverted, which makes the nuclide more stable. This additional stability requires more energy for an external nucleus to break the existing one and penetrate it.{{Cite web|url=http://n-t.ru/ri/ps/pb106.htm|title=Популярная библиотека химических элементов. Сиборгий (экавольфрам)|trans-title=Popular library of chemical elements. Seaborgium (eka-tungsten)|language=ru|website=n-t.ru|access-date=2020-01-07|archive-date=23 August 2011|archive-url=https://web.archive.org/web/20110823090114/http://n-t.ru/ri/ps/pb106.htm|url-status=live}} Reprinted from {{cite book|author=|date=1977|title=Популярная библиотека химических элементов. Серебро — Нильсборий и далее|chapter=Экавольфрам|trans-title=Popular library of chemical elements. Silver through nielsbohrium and beyond|trans-chapter=Eka-tungsten|language=ru|publisher=Nauka}} More energy diverted to binding nucleons means less rest energy, which in turn means less mass (mass is proportional to rest energy). More equal atomic numbers of the reacting nuclei result in greater electrostatic repulsion between them, but the lower mass excess of the target nucleus balances it. This leaves less excitation energy for the new compound nucleus, which necessitates fewer neutron ejections to reach a stable state. Due to this energy difference, the former mechanism became known as "hot fusion" and the latter as "cold fusion".{{Cite journal|last=Oganessian|first=Yu. Ts.|date=2000|title=Route to islands of stability of superheavy elements|journal=Physics of Atomic Nuclei |volume=63|issue=8|page=1320|doi=10.1134/1.1307456|bibcode=2000PAN....63.1315O|s2cid=121690628|issn=1063-7788}}

Cold fusion was first declared successful in 1974 at JINR, when it was tested for synthesis of the yet-undiscovered element{{spaces}}106. These new nuclei were projected to decay via spontaneous fission. The physicists at JINR concluded element 106 was produced in the experiment because no fissioning nucleus known at the time showed parameters of fission similar to what was observed during the experiment and because changing either of the two nuclei in the reactions negated the observed effects. Physicists at Lawrence Berkeley Laboratory (LBL; originally Radiation Laboratory, RL, and later Lawrence Berkeley National Laboratory, LBNL) of the University of California in Berkeley, California, United States, also expressed great interest in the new technique. When asked about how far this new method could go and if lead targets were a physics' Klondike, Oganessian responded, "Klondike may be an exaggeration [...] But soon, we will try to get elements 107{{spaces}}... 108 in these reactions."

= Reports =

Synthesis of element{{spaces}}108 was first attempted in 1978 by a team led by Oganessian at JINR. The team used a reaction that would generate element{{spaces}}108, specifically, the isotope {{sup|270}}108,{{Efn|The superscript number to the left of a chemical symbol refers to the mass of the nuclide; for instance, {{sup|48}}Ca is calcium-48. In superheavy element research, elements that have not gotten a name and a symbol, are often called by their atomic number in lieu of symbols; if a symbol has been assigned and the number is to be displayed, it is written in subscript to the left of the symbol. {{sup|270}}108 would be {{sup|270}}Hs or {{nuclide|hassium|270}} or hassium-270 in modern nomenclature.}} from fusion of radium (specifically, the isotope {{nowrap|{{Nuclide|radium|226}})}} and calcium {{nowrap|({{Nuclide|calcium|48}})}}. The researchers were uncertain in interpreting their data, and their paper did not unambiguously claim to have discovered the element.{{cite report |first1=Yu. Ts. |last1=Oganessian |first2=G. M. |last2=Ter-Akopian |first3=A. A. |last3=Pleve |display-authors=etal |year=1978 |title=Опыты по синтезу 108 элемента в реакции {{sup|226}}Ra + {{sup|48}}Ca |trans-title=Experiments on synthesis of element{{spaces}}108 in the {{sup|226}}Ra+{{sup|48}}Ca reaction |publisher=Joint Institute for Nuclear Research |url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/13/643/13643968.pdf |access-date=8 June 2018 |language=ru |archive-date=15 March 2020 |archive-url=https://web.archive.org/web/20200315080910/https://inis.iaea.org/collection/NCLCollectionStore/_Public/13/643/13643968.pdf |url-status=live }} The same year, another team at JINR investigated the possibility of synthesis of element{{spaces}}108 in reactions between lead {{nowrap|({{Nuclide|lead|208}})}} and iron {{nowrap|({{Nuclide|iron|58}})}}; they were uncertain in interpreting the data, suggesting the possibility that element{{spaces}}108 had not been created.{{Cite report|last1=Orlova|first1=O. A.|last2=Pleve|first2=A. A.|last3=Ter-Akop'yan|first3=G. M.|last4=Tret'yakova|first4=S. P.|last5=Chepigin|first5=V. I.|last6=Cherepanov|first6=E. A.|display-authors=3|date=1979|title=Опыты по синтезу 108 элемента в реакции {{sup|208}}Pb + {{sup|58}}Fe|trans-title=Experiments on the synthesis of element 108 in the {{sup|208}}Pb + {{sup|58}}Fe reaction|url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/10/486/10486434.pdf|language=ru|publisher=Joint Institute for Nuclear Research|access-date=2020-08-28|archive-date=11 March 2020|archive-url=https://web.archive.org/web/20200311041124/https://inis.iaea.org/collection/NCLCollectionStore/_Public/10/486/10486434.pdf|url-status=live}}

File:GSI, Darmstadt, Juli 2015 (4).JPG UNILAC, where hassium was discovered{{Cite web|title=Timeline—GSI|url=https://www.gsi.de/en/about_us/50_years_gsi/timeline_1969_2019.htm|publisher=GSI Helmholtz Centre for Heavy Ion Research|access-date=2019-12-10|archive-date=5 August 2020|archive-url=https://web.archive.org/web/20200805184050/https://www.gsi.de/en/about_us/50_years_gsi/timeline_1969_2019.htm|url-status=live}} and where its chemistry was first observed{{Cite news|last=Preuss|first=P.|date=2001|url=https://www2.lbl.gov/Science-Articles/Archive/108-chemistry.html|title=Hassium becomes heaviest element to have its chemistry studied|publisher=Lawrence Berkeley National Laboratory|access-date=2019-12-10|archive-date=10 December 2019|archive-url=https://web.archive.org/web/20191210155135/https://www2.lbl.gov/Science-Articles/Archive/108-chemistry.html|url-status=live}}|left]]

In 1983, new experiments were performed at JINR.{{sfn|Barber et al.|1993|p=1790}} The experiments probably resulted in the synthesis of element{{spaces}}108; bismuth {{nowrap|({{Nuclide|bismuth|209}})}} was bombarded with manganese {{nowrap|({{Nuclide|manganese|55}})}} to obtain {{sup|263}}108, lead ({{sup|207, 208}}Pb) was bombarded with iron ({{sup|58}}Fe) to obtain {{sup|264}}108, and californium {{nowrap|({{Nuclide|californium|249}})}} was bombarded with neon {{nowrap|({{Nuclide|neon|22}})}} to obtain {{sup|270}}108. These experiments were not claimed as a discovery and Oganessian announced them in a conference rather than in a written report.{{sfn|Barber et al.|1993|p=1790}}

In 1984, JINR researchers in Dubna performed experiments set up identically to the previous ones; they bombarded bismuth and lead targets with ions of manganese and iron, respectively. Twenty-one spontaneous fission events were recorded; the researchers concluded they were caused by {{sup|264}}108.{{sfn|Barber et al.|1993|p=1791}}

Later in 1984, a research team led by Peter Armbruster and Gottfried Münzenberg at Gesellschaft für Schwerionenforschung (GSI; Institute for Heavy Ion Research) in Darmstadt, Hesse, West Germany, tried to create element{{spaces}}108. The team bombarded a lead ({{sup|208}}Pb) target with accelerated iron ({{sup|58}}Fe) nuclei.{{Cite journal|doi=10.1007/BF01421260|title=The identification of element 108|year=1984|author=Münzenberg, G.|journal=Zeitschrift für Physik A|volume=317|pages=235|last2=Armbruster|first2=P.|last3=Folger|first3=H.|last4=Heßberger|first4=P. F.|last5=Hofmann|first5=S.|last6=Keller|first6=J.|last7=Poppensieker|first7=K.|last8=Reisdorf|first8=W.|last9=Schmidt|first9=K. -H.|bibcode = 1984ZPhyA.317..235M|issue=2 }} GSI's experiment to create element{{spaces}}108 was delayed until after their creation of element{{spaces}}109 in 1982, as prior calculations had suggested that even–even isotopes of element{{spaces}}108 would have spontaneous fission half-lives of less than one microsecond, making them difficult to detect and identify. The element{{spaces}}108 experiment finally went ahead after {{sup|266}}109 had been synthesized and was found to decay by alpha emission, suggesting that isotopes of element{{spaces}}108 would do likewise, and this was corroborated by an experiment aimed at synthesizing isotopes of element{{spaces}}106. GSI reported synthesis of three atoms of {{sup|265}}108. Two years later, they reported synthesis of one atom of the even–even {{sup|264}}108.{{cite journal |last1=Hofmann |first1=S. |date=2016 |title=The discovery of elements 107 to 112 |url=https://www.epj-conferences.org/articles/epjconf/pdf/2016/26/epjconf-NS160-06001.pdf |journal=EPJ Web Conf. |volume=131 |doi=10.1051/epjconf/201613106001 |access-date=23 September 2019 |pages=4–5 |bibcode=2016EPJWC.13106001H |doi-access=free |archive-date=1 February 2021 |archive-url=https://web.archive.org/web/20210201101405/https://www.epj-conferences.org/articles/epjconf/pdf/2016/26/epjconf-NS160-06001.pdf |url-status=live }}

= Arbitration =

In 1985, the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP) formed the Transfermium Working Group (TWG) to assess discoveries and establish final names for elements with atomic numbers greater than 100. The party held meetings with delegates from the three competing institutes; in 1990, they established criteria for recognition of an element and in 1991, they finished the work of assessing discoveries and disbanded. These results were published in 1993.{{sfn|Barber et al.|1993|p=1757}}

According to the report, the 1984 works from JINR and GSI simultaneously and independently established synthesis of element{{spaces}}108. Of the two 1984 works, the one from GSI was said to be sufficient as a discovery on its own. The JINR work, which preceded the GSI one, "very probably" displayed synthesis of element{{spaces}}108. However, that was determined in retrospect given the work from Darmstadt; the JINR work focused on chemically identifying remote granddaughters of element{{spaces}}108 isotopes (which could not exclude the possibility that these daughter isotopes had other progenitors), while the GSI work clearly identified the decay path of those element{{spaces}}108 isotopes. The report concluded that the major credit should be awarded to GSI.{{sfn|Barber et al.|1993|p=1791}} In written responses to this ruling, both JINR and GSI agreed with its conclusions. In the same response, GSI confirmed that they and JINR were able to resolve all conflicts between them.{{cite web |url=https://www.gsi.de/en/work/research/nustarenna/nustarenna_divisions/she_physik/research/super_heavy_elements/element_107_109.htm |title=GSI - Element 107-109 |website=GSI Helmholtz Centre for Heavy Ion Research |access-date=29 September 2019 |date=2012 |archive-date=29 September 2019 |archive-url=https://web.archive.org/web/20190929155340/https://www.gsi.de/en/work/research/nustarenna/nustarenna_divisions/she_physik/research/super_heavy_elements/element_107_109.htm |url-status=dead }}

= Naming =

Historically, a newly discovered element was named by its discoverer. The first regulation came in 1947, when IUPAC decided naming required regulation in case there are conflicting names.{{Efn|This was intended to resolve not only any future conflicts, but also a number of ones that existed back then: beryllium/glucinium, niobium/columbium, lutecium/cassiopeium, hafnium/celtium, tungsten/wolfram, and protactinium(protoactinium)/brevium.}} These matters were to be resolved by the Commission of Inorganic Nomenclature and the Commission of Atomic Weights. They would review the names in case of a conflict and select one; the decision would be based on a number of factors, such as usage, and would not be an indicator of priority of a claim. The two commissions would recommend a name to the IUPAC Council, which would be the final authority. The discoverers held the right to name an element, but their name would be subject to approval by IUPAC. The Commission of Atomic Weights distanced itself from element naming in most cases.{{Cite journal|last=Koppenol|first=W. H.|date=2002|title=Naming of new elements (IUPAC Recommendations 2002)|journal=Pure and Applied Chemistry|volume=74|issue=5|page=788|doi=10.1351/pac200274050787|s2cid=95859397|issn=1365-3075|url=http://doc.rero.ch/record/295589/files/pac200274050787.pdf|access-date=8 September 2020|archive-date=11 March 2023|archive-url=https://web.archive.org/web/20230311205341/https://doc.rero.ch/record/295589/files/pac200274050787.pdf|url-status=live}}

In Mendeleev's nomenclature for unnamed and undiscovered elements, hassium would be called "eka-osmium", as in "the first element below osmium in the periodic table" (from Sanskrit eka meaning "one"). In 1979, IUPAC published recommendations according to which the element was to be called "unniloctium" (symbol "Uno"),{{cite journal|last1=Chatt |first1=J.|journal=Pure and Applied Chemistry|date=1979|volume=51|issue=2 |pages=381–384|title=Recommendations for the naming of elements of atomic numbers greater than 100 |doi=10.1351/pac197951020381|doi-access=free}} a systematic element name as a placeholder until the element was discovered and the discovery then confirmed, and a permanent name was decided. Although these recommendations were widely followed in the chemical community, the competing physicists in the field ignored them.{{cite journal|last1=Öhrström|first1=L.|last2=Holden|first2=N. E.|date=2016 |title=The Three-Letter Element Symbols|journal=Chemistry International|volume=38 |issue=2|pages=4–8|doi=10.1515/ci-2016-0204|doi-access=free}}{{sfn|Greenwood|Earnshaw|1997|p=30}} They either called it "element{{spaces}}108", with the symbols E108, (108) or 108, or used the proposed name "hassium".{{sfn|Hoffman|Lee|Pershina|2006|p=1653}}

File:Coat of arms of Hesse.svg of the German state of Hesse, after which hassium is named]]

In 1990, in an attempt to break a deadlock in establishing priority of discovery and naming of several elements, IUPAC reaffirmed in its nomenclature of inorganic chemistry that after existence of an element was established, the discoverers could propose a name. (Also, the Commission of Atomic Weights was excluded from the naming process.) The first publication on criteria for an element discovery, released in 1991, specified the need for recognition by TWG.

Armbruster and his colleagues, the officially recognized German discoverers, held a naming ceremony for the elements 107 through 109, which had all been recognized as discovered by GSI, on 7{{spaces}}September 1992. For element{{spaces}}108, the scientists proposed the name "hassium".{{cite web |url=https://www.gsi.de/en/work/research/nustarenna/nustarenna_divisions/she_physik/research/super_heavy_elements/element_107_109.htm |title=GSI—Element 107-109 |publisher=GSI Helmholtz Centre for Heavy Ion Research |access-date=29 September 2019 |date=2012 |archive-date=29 September 2019 |archive-url=https://web.archive.org/web/20190929155340/https://www.gsi.de/en/work/research/nustarenna/nustarenna_divisions/she_physik/research/super_heavy_elements/element_107_109.htm |url-status=dead }} It is derived from the Latin name Hassia for the German state of Hesse where the institute is located. This name was proposed to IUPAC in a written response to their ruling on priority of discovery claims of elements, signed 29 September 1992.

The process of naming of element 108 was a part of a larger process of naming a number of elements starting with element 101; three teams—JINR, GSI, and LBL—claimed discovery of several elements and the right to name those elements. Sometimes, these claims clashed; since a discoverer was considered entitled to naming of an element, conflicts over priority of discovery often resulted in conflicts over names of these new elements. These conflicts became known as the Transfermium Wars.{{cite journal|last=Karol|first=P.|date=1994|title=The Transfermium Wars|journal=Chemical & Engineering News|volume=74|issue=22|pages=2–3|doi=10.1021/cen-v072n044.p002|doi-access=free}} Different suggestions to name the whole set of elements from 101 onward and they occasionally assigned names suggested by one team to be used for elements discovered by another.{{Efn|For example, Armbruster suggested element 107 be named nielsbohrium; JINR used this name for element 105 which they claimed to have discovered. This was meant to honor Oganessian's technique of cold fusion; GSI had asked JINR for permission.{{sfn|Hoffman|Ghiorso|Seaborg|2000|pp=337–338, 384}}}} However, not all suggestions were met with equal approval; the teams openly protested naming proposals on several occasions.{{sfn|Hoffman|Ghiorso|Seaborg|2000|pp=385–394}}

In 1994, IUPAC Commission on Nomenclature of Inorganic Chemistry recommended that element{{spaces}}108 be named "hahnium" (Hn) after German physicist Otto Hahn so elements named after Hahn and Lise Meitner (it was recommended element{{spaces}}109 should be named meitnerium, following GSI's suggestion) would be next to each other, honouring their joint discovery of nuclear fission;{{Cite journal|doi=10.1351/pac199466122419|title=Names and symbols of transfermium elements (IUPAC Recommendations 1994)|date=1994|journal=Pure and Applied Chemistry|volume=66|pages=2419–2421|issue=12|author=Inorganic Chemistry Division: Commission on Nomenclature of Inorganic Chemistry|url=http://publications.iupac.org/pac/pdf/1994/pdf/6612x2419.pdf|access-date=2020-08-28|archive-date=11 October 2021|archive-url=https://web.archive.org/web/20211011045418/http://publications.iupac.org/pac/pdf/1994/pdf/6612x2419.pdf|url-status=live}} IUPAC commented that they felt the German suggestion was obscure.{{cite journal |last1=Cotton |first1=S. A. |date=1996 |title=After the actinides, then what? |journal=Chemical Society Reviews |volume=25 |issue=3 |pages=219–227 |doi=10.1039/CS9962500219}} GSI protested, saying this proposal contradicted the long-standing convention of giving the discoverer the right to suggest a name;{{cite web |url=http://www-alt.gsi.de/documents/DOC-2003-Jun-35-5.pdf |title=IUPAC verabschiedet Namen für schwere Elemente: GSI-Vorschläge für die Elemente 107 bis 109 akzeptiert |language=de |trans-title=IUPAC adopts names for heavy elements: GSI's suggestions for elements 107 to 109 accepted |date=1997 |website=GSI-Nachrichten |publisher=Gesellschaft für Schwerionenforschung |access-date=30 June 2019 |archive-url=https://web.archive.org/web/20151223025747/https://www-alt.gsi.de/documents/DOC-2003-Jun-35-5.pdf |archive-date=23 December 2015}} the American Chemical Society supported GSI. The name "hahnium", albeit with the different symbol Ha, had already been proposed and used by the American scientists for element{{spaces}}105, for which they had a discovery dispute with JINR; they thus protested the confusing scrambling of names.{{Cite web|url=http://www2.lbl.gov/Science-Articles/Archive/seaborgium-dispute.html|title=Naming of element{{spaces}}106 disputed by international committee|last=Yarris|first=L.|year=1994|publisher=Lawrence Berkeley Laboratory|access-date=September 7, 2016|archive-date=1 July 2016|archive-url=https://web.archive.org/web/20160701203756/http://www2.lbl.gov/Science-Articles/Archive/seaborgium-dispute.html|url-status=live}} Following the uproar, IUPAC formed an ad hoc committee of representatives from the national adhering organizations of the three countries home to the competing institutions; they produced a new set of names in 1995. Element{{spaces}}108 was again named hahnium; this proposal was also retracted.{{sfn|Hoffman|Ghiorso|Seaborg|2000|pp=392–394}} The final compromise was reached in 1996 and published in 1997; element{{spaces}}108 was named hassium (Hs).{{sfn|Hoffman|Ghiorso|Seaborg|2000|pp=394–395}} Simultaneously, the name dubnium (Db; from Dubna, the JINR location) was assigned to element{{spaces}}105, and the name hahnium was not used for any element.{{Cite journal|last=Bera|first=J. K.|year=1999|title=Names of the Heavier Elements |journal=Resonance|volume=4|issue=3|pages=53–61|doi=10.1007/BF02838724|s2cid=121862853}}{{cite journal | doi=10.1351/pac199769122471|title=Names and symbols of transfermium elements (IUPAC Recommendations 1997) | year=1997 | journal=Pure and Applied Chemistry | volume=69 | pages=2471–2474 | issue=12| doi-access=free }}{{efn|American physicist Glenn T. Seaborg suggested that name for element{{spaces}}110 on behalf of LBNL in November 1997 after IUPAC surveyed the three main collaborations (GSI, JINR/LLNL, and LBNL) on how they thought the element should be named.{{sfn|Hoffman|Ghiorso|Seaborg|2000|pp=396–398}}}}

The official justification for this naming, alongside that of darmstadtium for element{{spaces}}110, was that it completed a set of geographic names for the location of the GSI; this set had been initiated by 19th-century names europium and germanium. This set would serve as a response to earlier naming of americium, californium, and berkelium for elements discovered in Berkeley. Armbruster commented on this, "this bad tradition{{efn|Similarly, there are names of ruthenium, moscovium, and dubnium for JINR. The only element discovered by RIKEN in Wakō, Saitama Prefecture, Japan, is named nihonium after a Japanese name of Japan.}} was established by Berkeley. We wanted to do it for Europe." Later, when commenting on the naming of element{{spaces}}112, Armbruster said, "I did everything to ensure that we do not continue with German scientists and German towns."{{cite book |last=Aldersey-Williams |first=H. |author-link=Hugh Aldersey-Williams |title=Periodic Tales |date=2011 |publisher=HarperCollins Publishers |isbn=978-0-06-182473-9 |pages=396–397|title-link=Periodic Tales }}

Isotopes

{{Isotopes summary

|element=hassium

|other_notes={{efn|Few nuclei of each hassium isotope have been synthesized, and thus half-lives of these isotopes cannot be determined very precisely. Therefore, a half-life may be given as the most likely value alongside a confidence interval that corresponds to one standard deviation (such an interval based on future experiments, whose result is yet unknown, contains the true value with a probability of ~68.3%): for example, the value of 1.42{{spaces}}s in the isotope table obtained for ²⁶⁸Hs was listed in the source as 1.42{{spaces}}±1.13{{spaces}}s, and this value is a modification of the value of {{nowrap|0.38{{su|p=+1.8|b=−0.17}} s}}.{{sfn|Audi et al.|2017|p=030001-134}}}}

|year_ref={{sfn|Audi et al.|2017|p=030001-133}}

|reaction_ref={{Thoennessen2016|pages=229, 234, 238}}{{efn|The notation ²⁰⁸Pb(⁵⁶Fe,n)²⁶³Hs denotes a nuclear reaction between a nucleus of ²⁰⁸Pb that was bombarded with a nucleus of ⁵⁶Fe; the two fused, and after a single neutron had been emitted, the remaining nucleus was ²⁶³Hs. Another notation for this reaction would be ²⁰⁸Pb + ⁵⁶Fe → ²⁶³Hs + n.}}

|isotopes=

{{isotopes summary/isotope

|mn=263 |sym=Hs |hl={{sort|760|760 μs}}|ref={{sfn|Audi et al.|2017|p=030001-133}}

|dm=α, SF |year=2009|re=²⁰⁸Pb(⁵⁶Fe,n)

}}

{{isotopes summary/isotope

|mn=264|sym=Hs|hl={{sort|540|540 μs}}|ref={{sfn|Audi et al.|2017|p=030001-133}}|dm=α, SF|year=1986|re=²⁰⁷Pb(⁵⁸Fe,n)

}}

{{isotopes summary/isotope

|mn=265|sym=Hs|hl={{sort|1960|1.96 ms}}|ref={{sfn|Audi et al.|2017|p=030001-133}}|dm=α, SF|year=1984|re=²⁰⁸Pb(⁵⁸Fe,n)

}}

{{isotopes summary/isotope

|mn=265m|sym=Hs|hl={{sort|360|360 μs}}|ref={{sfn|Audi et al.|2017|p=030001-133}}|dm=α|year=1995|re=²⁰⁸Pb(⁵⁸Fe,n)

}}

{{isotopes summary/isotope

|mn=266|sym=Hs|hl={{sort|3020|3.02 ms}}|ref={{sfn|Audi et al.|2017|p=030001-133}}|dm=α, SF|year=2001|re=²⁷⁰Ds(—,α)

}}

{{isotopes summary/isotope

|mn=266m|sym=Hs|hl={{sort|280000|280 ms}}|ref={{sfn|Audi et al.|2017|p=030001-133}}|dm=α|year=2011|re=^270mDs(—,α)

}}

{{isotopes summary/isotope

|mn=267|sym=Hs|hl={{sort|55000|55 ms}}|ref={{sfn|Audi et al.|2017|p=030001-134}}|dm=α|year=1995|re=²³⁸U(³⁴S,5n)

}}

{{isotopes summary/isotope

|mn=267m|sym=Hs|hl={{sort|990|990 μs}}|ref={{sfn|Audi et al.|2017|p=030001-134}}|dm=α|year=2004|re=²³⁸U(³⁴S,5n)

}}

{{isotopes summary/isotope

|mn=268|sym=Hs|hl={{sort|1420000|1.42 s}}|ref={{sfn|Audi et al.|2017|p=030001-134}}|dm=α|year=2010|re=²³⁸U(³⁴S,4n)

}}

{{isotopes summary/isotope

|mn=269|sym=Hs|hl={{sort|13000000|13 s}}|ref=|dm=α|year=1996|re=²⁷⁷Cn(—,2α)

}}

{{isotopes summary/isotope

|mn=269m|sym=Hs|hl={{sort|2800000|2.8 s}}|ref=|dm=α, IT|year=2024|re=²⁷³Ds(—,α)

}}

{{isotopes summary/isotope

|mn=270|sym=Hs|hl={{sort|7600000|7.6 s}}|ref={{sfn|Audi et al.|2017|p=030001-134}}|dm=α|year=2003|re=²⁴⁸Cm(²⁶Mg,4n)

}}

{{isotopes summary/isotope

|mn=271|sym=Hs|hl={{sort|46000000|46 s}}|ref={{cite journal |last1=Oganessian |first1=Yu. Ts. |last2=Utyonkov |first2=V. K. |last3=Shumeiko |first3=M. V. |last4=Abdullin |first4=F. Sh. |last5=Adamian |first5=G. G. |last6=Dmitriev |first6=S. N. |last7=Ibadullayev |first7=D. |last8=Itkis |first8=M. G. |last9=Kovrizhnykh |first9=N. D. |last10=Kuznetsov |first10=D. A. |last11=Petrushkin |first11=O. V. |last12=Podshibiakin |first12=A. V. |last13=Polyakov |first13=A. N. |last14=Popeko |first14=A. G. |last15=Rogov |first15=I. S. |last16=Sagaidak |first16=R. N. |last17=Schlattauer |first17=L. |last18=Shubin |first18=V. D. |last19=Solovyev |first19=D. I. |last20=Tsyganov |first20=Yu. S. |last21=Voinov |first21=A. A. |last22=Subbotin |first22=V. G. |last23=Bublikova |first23=N. S. |last24=Voronyuk |first24=M. G. |last25=Sabelnikov |first25=A. V. |last26=Bodrov |first26=A. Yu. |last27=Aksenov |first27=N. V. |last28=Khalkin |first28=A. V. |last29=Gan |first29=Z. G. |last30=Zhang |first30=Z. Y. |last31=Huang |first31=M. H. |last32=Yang |first32=H. B. |display-authors=3 |title=Synthesis and decay properties of isotopes of element 110: Ds 273 and Ds 275 |journal=Physical Review C |date=6 May 2024 |volume=109 |issue=5 |page=054307 |doi=10.1103/PhysRevC.109.054307 |url=https://journals.aps.org/prc/pdf/10.1103/PhysRevC.109.054307 |access-date=11 May 2024 |language=en |issn=2469-9985 |bibcode=2024PhRvC.109e4307O}}|dm=α|year=2008|re=²⁴⁸Cm(²⁶Mg,3n)

}}

{{isotopes summary/isotope

|mn=271m|sym=Hs|hl={{sort|7100000|7.1 s}}|ref=|dm=α, IT|year=2024|re=²⁷⁵Ds(—,α)

}}

{{isotopes summary/isotope

|mn=272|sym=Hs|hl={{sort|160000|160 ms}}|ref={{cite journal |title=New isotope ²⁷⁶Ds and its decay products ²⁷²Hs and ²⁶⁸Sg from the ²³²Th + ⁴⁸Ca reaction |last1=Oganessian |first1=Yu. Ts. |last2=Utyonkov |first2=V. K. |last3=Shumeiko |first3=M. V. |display-authors=et al. |date=2023 |journal=Physical Review C |volume=108 |number=24611 |page=024611 |doi=10.1103/PhysRevC.108.024611|bibcode=2023PhRvC.108b4611O |s2cid=261170871 }}|dm=α|year=2022|re=²⁷⁶Ds(—,α)

}}

{{isotopes summary/isotope

|mn=273|sym=Hs|hl={{sort|510000|510 ms}}|ref={{cite journal |last1=Utyonkov |first1=V. K. |last2=Brewer |first2=N. T. |first3=Yu. Ts. |last3=Oganessian |display-authors=3 |first4=K. P. |last4=Rykaczewski |first5=F. Sh. |last5=Abdullin |first6=S. N. |last6=Dimitriev |first7=R. K. |last7=Grzywacz |first8=M. G. |last8=Itkis |first9=K. |last9=Miernik |first10=A. N. |last10=Polyakov |first11=J. B. |last11=Roberto |first12=R. N. |last12=Sagaidak |first13=I. V. |last13=Shirokovsky |first14=M. V. |last14=Shumeiko |first15=Yu. S. |last15=Tsyganov |first16=A. A. |last16=Voinov |first17=V. G. |last17=Subbotin |first18=A. M. |last18=Sukhov |first19=A. V. |last19=Karpov |first20=A. G. |last20=Popeko |first21=A. V. |last21=Sabel'nikov |first22=A. I. |last22=Svirikhin |first23=G. K. |last23=Vostokin |first24=J. H. |last24=Hamilton |first25=N. D. |last25=Kovrinzhykh |first26=L. |last26=Schlattauer |first27=M. A. |last27=Stoyer |first28=Z. |last28=Gan |first29=W. X. |last29=Huang |first30=L. |last30=Ma |date=30 January 2018 |title=Neutron-deficient superheavy nuclei obtained in the ²⁴⁰Pu+⁴⁸Ca reaction |journal=Physical Review C |volume=97 |issue=14320 |pages=014320 |doi=10.1103/PhysRevC.97.014320|bibcode=2018PhRvC..97a4320U |doi-access=free }}|dm=α|year=2010|re=²⁸⁵Fl(—,3α)

}}

{{isotopes summary/isotope

|mn=275|sym=Hs|hl={{sort|600000|600 ms}}|ref={{cite journal |title=Investigation of ⁴⁸Ca-induced reactions with ²⁴²Pu and ²³⁸U targets at the JINR Superheavy Element Factory |journal=Physical Review C |volume=106 |number=24612 |year=2022 |first1=Yu. Ts. |last1=Oganessian |first2=V. K. |last2=Utyonkov |first3=D. |last3=Ibadullayev |page=024612 |display-authors=et al. |doi= 10.1103/PhysRevC.106.024612|bibcode=2022PhRvC.106b4612O |osti=1883808 |s2cid=251759318 }}|dm=α|year=2004|re=²⁸⁷Fl(—,3α)

}}

{{isotopes summary/isotope

|mn=277|sym=Hs|hl={{sort|12000|12 ms}}|ref={{sfn|Audi et al.|2017|p=030001-136}}|dm=α|year=2010|re=²⁸⁹Fl(—,3α)

}}

{{isotopes summary/isotope

|mn=277m|sym=Hs|hl={{sort|130000000|130 s}}{{efn|name=unconfirmed|Only one event of decay of this isotope has been registered.}}|ref={{sfn|Audi et al.|2017|p=030001-136}}{{NUBASE2020}}|dm=SF|year=2012|re=^293mLv(—,4α)

}}

Hassium has no stable or naturally occurring isotopes. Several radioisotopes have been synthesized in the lab, either by fusing two atoms or by observing the decay of heavier elements. As of 2019, the quantity of all hassium ever produced was on the order of hundreds of atoms.{{Cite book |last=Scerri|first=E.|title=The Periodic Table: Its Story and Its Significance|publisher=Oxford University Press |url=https://books.google.com/books?id=tSa3DwAAQBAJ&q=hassium+100+atoms+scerri&pg=PA360 |date=2019|isbn=978-0-19-091438-7|author-link=Eric Scerri}}{{Cite web|last=Helmenstine|first=A. M.|date=2019|title=Hassium Facts—Hs or Element 108 |url=https://www.thoughtco.com/hassium-facts-4136901|url-status=dead|archive-url=https://web.archive.org/web/20200801143047/https://www.thoughtco.com/hassium-facts-4136901|archive-date=1 August 2020|access-date=2020-07-09|website=ThoughtCo}} Thirteen isotopes with mass numbers 263 through 277 (except for 274 and 276) have been reported, six of which—{{sup|265, 266, 267, 269, 271, 277}}Hs—have known metastable states,{{sfn|Audi et al.|2017|pp=030001-133–030001-136}}{{efn|Metastable nuclides are denoted by the letter "m" immediately the mass number, such as in "hassium-277m" aka {{sup|277m}}Hs.}} though that of {{sup|277}}Hs is unconfirmed.{{cite journal|last1=Hofmann|first1=S.|last2=Heinz|first2=S.|last3=Mann|first3=R.|last4=Maurer|first4=J. |last5=Khuyagbaatar|first5=J.|last6=Ackermann|first6=D.|last7=Antalic|first7=S.|last8=Barth|first8=W. |last9=Block|first9=M. |last10=Burkhard|first10=H. G.|last11=Comas|first11=V. F.|display-authors=3 |last12=Dahl|first12=L.|last13=Eberhardt|first13=K.|last14=Gostic|first14=J.|last15=Henderson|first15=R. A. |last16=Heredia|first16=J. A.|last17=Heßberger |first17=F. P.|last18=Kenneally|first18=J. M.|last19=Kindler |first19=B.|last20=Kojouharov|first20=I.|last21=Kratz|first21=J. V.|last22=Lang|first22=R.|last23=Leino |first23=M. |year=2012|title=The reaction ⁴⁸Ca + ²⁴⁸Cm → ²⁹⁶116^* studied at the GSI-SHIP|journal=The European Physical Journal A|volume=48|issue=5|pages=62 |bibcode=2012EPJA...48...62H|doi=10.1140/epja/i2012-12062-1|last24=Lommel|first24=B. |last25=Moody |first25=K. J.|last26=Münzenberg|first26=G.|last27=Nelson|first27=S. L.|last28=Nishio|first28=K. |last29=Popeko|first29=A. G.|last30=Runke|first30=J.|s2cid=121930293}} Most of these isotopes decay mainly through alpha decay; this is the most common for all isotopes for which comprehensive decay characteristics are available; the only exception is {{sup|277}}Hs, which undergoes spontaneous fission.{{sfn|Audi et al.|2017|pp=030001-133–030001-136}} Lighter isotopes were usually synthesized by direct fusion of two nuclei, whereas heavier isotopes were typically observed as decay products of nuclei with larger atomic numbers.

Atomic nuclei have well-established nuclear shells, which make nuclei more stable. If a nucleus has certain numbers (magic numbers) of protons or neutrons, that complete a nuclear shell, then the nucleus is even more stable against decay. The highest known magic numbers are 82 for protons and 126 for neutrons. This notion is sometimes expanded to include additional numbers between those magic numbers, which also provide some additional stability and indicate closure of "sub-shells". Unlike the better-known lighter nuclei, superheavy nuclei are deformed. Until the 1960s, the liquid drop model was the dominant explanation for nuclear structure. It suggested that the fission barrier would disappear for nuclei with ~280{{spaces}}nucleons.{{Cite web|last=Pauli|first=N.|date=2019|title=Nuclear fission|url=http://metronu.ulb.ac.be/npauly/Pauly/physnu/chapter_8.pdf|access-date=2020-02-16|work=Introductory Nuclear, Atomic and Molecular Physics (Nuclear Physics Part)|publisher=Université libre de Bruxelles|archive-date=21 October 2021|archive-url=https://web.archive.org/web/20211021225818/http://metronu.ulb.ac.be/npauly/Pauly/physnu/chapter_8.pdf|url-status=live}}{{Cite journal|last=Oganessian|first=Yu. Ts.|date=2004|title=Superheavy elements|journal=Pure and Applied Chemistry|volume=76|issue=9|pages=1716–1718|doi=10.1351/pac200476091715|issn=1365-3075|doi-access=free}} It was thus thought that spontaneous fission would occur nearly instantly before nuclei could form a structure that could stabilize them; it appeared that nuclei with Z{{spaces}}≈{{spaces}}103{{efn|"Z" means atomic number—number of protons. "N" means neutron number—number of neutrons. "A" means mass number—combined number of neutrons and protons.}} were too heavy to exist for a considerable length of time.{{Cite magazine|last=Dean|first=T.|date=2014|title=How to make a superheavy element|url=https://cosmosmagazine.com/physics/how-make-superheavy-element/|access-date=2020-07-04|magazine=Cosmos Magazine|archive-date=4 July 2020|archive-url=https://web.archive.org/web/20200704160434/https://cosmosmagazine.com/physics/how-make-superheavy-element/|url-status=dead}}

The later nuclear shell model suggested that nuclei with ~300 nucleons would form an island of stability where nuclei will be more resistant to spontaneous fission and will mainly undergo alpha decay with longer half-lives, and the next doubly magic nucleus (having magic numbers of both protons and neutrons) is expected to lie in the center of the island of stability near Z{{spaces}}={{spaces}}110–114 and the predicted magic neutron number N{{spaces}}={{spaces}}184. Subsequent discoveries suggested that the predicted island might be further than originally anticipated. They also showed that nuclei intermediate between the long-lived actinides and the predicted island are deformed, and gain additional stability from shell effects, against alpha decay and especially against spontaneous fission. The center of the region on a chart of nuclides that would correspond to this stability for deformed nuclei was determined as {{sup|270}}Hs, with 108 expected to be a magic number for protons for deformed nuclei—nuclei that are far from spherical—and 162 a magic number for neutrons for such nuclei.{{Cite journal|last=Schädel|first=M.|title=Chemistry of the superheavy elements|journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences |date=2015|volume=373|issue=2037|pages=20140191|doi=10.1098/rsta.2014.0191 |pmid=25666065|bibcode=2015RSPTA.37340191S|issn=1364-503X|doi-access=free}} Experiments on lighter superheavy nuclei,{{Cite conference|last=Hulet |first=E. K.|date=1989|title=Biomodal spontaneous fission|conference=50th Anniversary of Nuclear Fission|bibcode=1989nufi.rept...16H}} as well as those closer to the expected island, have shown greater than previously anticipated stability against spontaneous fission, showing the importance of shell effects on nuclei.

Theoretical models predict a region of instability for some hassium isotopes to lie around A{{spaces}}={{spaces}}275{{sfn|Zagrebaev|Karpov|Greiner|2013|pages=11–12}} and N{{spaces}}={{spaces}}168–170, which is between the predicted neutron shell closures at N{{spaces}}={{spaces}}162 for deformed nuclei and N{{spaces}}={{spaces}}184 for spherical nuclei.{{Cite journal|last1=Oganessian |first1=Yu. Ts.|last2=Abdullin|first2=F. Sh. |last3=Alexander|first3=C.|last4=Binder|first4=J.|last5=Boll |first5=R. A.|last6=Dmitriev|first6=S. N.|last7=Ezold|first7=J.|last8=Felker|first8=K.|last9=Gostic |first9=J. M.|display-authors=3|date=2013|title=Experimental studies of the ²⁴⁹Bk + ⁴⁸Ca reaction including decay properties and excitation function for isotopes of element{{spaces}}117, and discovery of the new isotope ²⁷⁷Mt|journal=Physical Review C |volume=87 |issue=5|pages=8–9|publisher=American Physical Society |bibcode=2013PhRvC..87e4621O |doi=10.1103/PhysRevC.87.054621|doi-access=free}} Nuclides in this region are predicted to have low fission barrier heights, resulting in short partial half-lives toward spontaneous fission. This prediction is supported by the observed 11-millisecond half-life of {{sup|277}}Hs and the 5-millisecond half-life of the neighbouring isobar {{sup|277}}Mt because the hindrance factors from the odd nucleon were shown to be much lower than otherwise expected. The measured half-lives are even lower than those originally predicted for the even–even {{sup|276}}Hs and {{sup|278}}Ds, which suggests a gap in stability away from the shell closures and perhaps a weakening of the shell closures in this region.

In 1991, Polish physicists Zygmunt Patyk and Adam Sobiczewski predicted{{Cite journal|last1=Patyk|first1=Z.|last2=Sobiczewski|first2=A.|date=1991|title=Ground-state properties of the heaviest nuclei analyzed in a multidimensional deformation space|journal=Nuclear Physics A|volume=533|issue=1|page=150|bibcode=1991NuPhA.533..132P|doi=10.1016/0375-9474(91)90823-O}} that 108 is a proton magic number for deformed nuclei and 162 is a neutron magic number for such nuclei. This means such nuclei are permanently deformed in their ground state but have high, narrow fission barriers to further deformation and hence relatively long spontaneous-fission half-lives.{{cite magazine|last=Inman|first=M.|date=2006|title=A Nuclear Magic Trick|magazine=Physical Review Focus |volume=18|url=https://physics.aps.org/story/v18/st19|access-date=2006-12-25|url-status=live |archive-url=https://web.archive.org/web/20180602001137/https://physics.aps.org/story/v18/st19|archive-date=2 June 2018|doi=10.1103/physrevfocus.18.19}}{{cite journal|last1=Dvorak|first1=J.|last2=Brüchle|first2=W.|last3=Chelnokov|first3=M.|last4=Dressler|first4=R.|last5=Düllmann|first5=Ch. E.|last6=Eberhardt|first6=K.|last7=Gorshkov|first7=V.|last8=Jäger|first8=E.|last9=Krücken|first9=R.|last10=Kuznetsov|first10=A.|last11=Nagame|first11=Y.|last12=Nebel|first12=F.|last13=Novackova|first13=Z.|display-authors=3|date=2006|title=Doubly Magic Nucleus ₁₀₈²⁷⁰Hs₁₆₂|url=https://www.dora.lib4ri.ch/psi/islandora/object/psi%3A16351|journal=Physical Review Letters|volume=97|issue=24|pages=242501|bibcode=2006PhRvL..97x2501D|doi=10.1103/PhysRevLett.97.242501|pmid=17280272|last24=Yeremin|first24=A.|last23=Yakushev|first23=A.|last22=Wierczinski|first22=B.|last21=Wegrzecki|first21=M.|last20=Türler|first20=A.|last19=Thörle|first19=P.|last18=Semchenkov|first18=A.|last17=Schimpf|first17=E.|last16=Schausten|first16=B.|first15=M.|last15=Schädel|last14=Qin|first14=Z.|access-date=20 August 2019|archive-date=16 November 2019|archive-url=https://web.archive.org/web/20191116170013/https://www.dora.lib4ri.ch/psi/islandora/object/psi:16351|url-status=live}} Computational prospects for shell stabilization for {{sup|270}}Hs made it a promising candidate for a deformed doubly magic nucleus.{{Cite journal|last=Smolańczuk|first=R.|date=1997|title=Properties of the hypothetical spherical superheavy nuclei|journal=Physical Review C|url=https://www.dora.lib4ri.ch/psi/islandora/object/psi%3A16351/datastream/PDF/Dvorak-2006-Doubly_magic_nucleus_108270Hs162-%28published_version%29.pdf|volume=56|issue=2|pages=812–824|bibcode=1997PhRvC..56..812S|doi=10.1103/PhysRevC.56.812|access-date=21 October 2019|archive-date=21 October 2019|archive-url=https://web.archive.org/web/20191021125835/https://www.dora.lib4ri.ch/psi/islandora/object/psi:16351/datastream/PDF/Dvorak-2006-Doubly_magic_nucleus_108270Hs162-(published_version).pdf|url-status=live}} Experimental data is scarce, but the existing data is interpreted by the researchers to support the assignment of N{{spaces}}={{spaces}}162 as a magic number. In particular, this conclusion was drawn from the decay data of {{sup|269}}Hs, {{sup|270}}Hs, and {{sup|271}}Hs.{{efn|In particular, the low decay energy for ²⁷⁰Hs matches calculations. The conclusion for ²⁶⁹Hs was made after its decay data was compared to that of ²⁷³Ds; the decay of the latter into the former has an energy sufficiently greater than the decay of the former (11.2{{spaces}}MeV and 9.2{{spaces}}MeV, respectively). The great value of the former energy was explained as a right-to-left crossing of N{{spaces}}{{=}}{{spaces}}162 (²⁷³Ds has 163 neutrons and ²⁶⁹Hs has 161).{{cite journal|last1=Hofmann |first1=S.|last2=Heßberger|first2=F.P.|last3=Ackermann|first3=D.|display-authors=3|last4=Münzenberg |first4=G.|last5=Antalic|first5=S.|last6=Cagarda|first6=P. |last7=Kindler|first7=B.|last8=Kojouharova |first8=J.|last9=Leino|first9=M.|last10=Lommel|first10=B.|last11=Mann|first11=R.|date=2002|title=New results on elements 111 and 112|journal=The European Physical Journal A|volume=14 |issue=2|page=155 |doi=10.1140/epja/i2001-10119-x|issn=1434-6001|bibcode=2002EPJA...14..147H|s2cid=8773326}} A similar observation and conclusion were made after measurement of decay energy of ²⁷¹Hs and ²⁶⁷Sg.{{cite book|last1=Schädel|first1=M.|last2=Shaughnessy|first2=D.|date=2013|title=The Chemistry of Superheavy Elements|url=https://books.google.com/books?id=ei-_BAAAQBAJ|publisher=Springer Science & Business Media|isbn=978-3-642-37466-1|page=458|access-date=17 May 2020|archive-date=8 October 2024|archive-url=https://web.archive.org/web/20241008102954/https://books.google.com/books?id=ei-_BAAAQBAJ|url-status=live}}}} In 1997, Polish physicist Robert Smolańczuk calculated that the isotope {{sup|292}}Hs may be the most stable superheavy nucleus against alpha decay and spontaneous fission as a consequence of the predicted N{{spaces}}={{spaces}}184 shell closure.{{cite journal|last1=Karpov|first1=A. V.|last2=Zagrebaev|first2=V. I.|last3=Palenzuela|first3=Y. M. |last4=Ruiz|first4=L. F.|last5=Greiner |first5=W.|display-authors=3|date=2012|title=Decay properties and stability of the heaviest elements|url=http://nrv.jinr.ru/karpov/publications/Karpov12_IJMPE.pdf |url-status=live|journal=International Journal of Modern Physics E |volume=21 |issue=2|pages=1250013-1–1250013-20|bibcode=2012IJMPE..2150013K|doi=10.1142/S0218301312500139|archive-url=https://web.archive.org/web/20161203230540/http://nrv.jinr.ru/karpov/publications/Karpov12_IJMPE.pdf |archive-date=3 December 2016|access-date=28 December 2018}}

Natural occurrence

File:Molybdenit 1.jpg|right]]

Hassium is not known to occur naturally on Earth; all its known isotopes are so short-lived that no primordial hassium would survive to today. This does not rule out the possibility of unknown, longer-lived isotopes or nuclear isomers, some of which could still exist in trace quantities if they are long-lived enough. As early as 1914, German physicist Richard Swinne proposed element{{spaces}}108 as a source of X-rays in the Greenland ice sheet. Though Swinne was unable to verify this observation and thus did not claim discovery, he proposed in 1931 the existence of "regions" of long-lived transuranic elements, including one around Z{{spaces}}={{spaces}}108.{{sfn|Kragh|2018|pages=9–10}}

In 1963, Soviet geologist and physicist Viktor Cherdyntsev, who had previously claimed the existence of primordial curium-247,{{cite journal |last1=Cherdyntsev |first1=V. V. |last2=Mikhailov |first2=V. F. |date=1963 |title=Первозданный заурановый изотоп в природе |trans-title=The Primordial Transuranium Isotope in Nature |journal=Geokhimiya |volume=1 |pages=3–14 |osti=4748393 |language=ru}} claimed to have discovered element{{spaces}}108—specifically the {{sup|267}}108 isotope, which supposedly had a half-life of 400 to 500{{spaces}}million years—in natural molybdenite and suggested the provisional name sergenium (symbol Sg);{{efn|At the time, this symbol had not yet been taken by seaborgium.}} this name comes from the name for the Silk Road and was explained as "coming from Kazakhstan" for it.{{Cite journal|last=Nikitin|first=A.|date=1970|title=Новый трансуран найден в природе|trans-title=New transuranium found in nature|journal=Nauka i Zhizn|language=ru|volume=2|pages=102–106}} His rationale for claiming that sergenium was the heavier homologue to osmium was that minerals supposedly containing sergenium formed volatile oxides when boiled in nitric acid, similarly to osmium.

Soviet physicist Vladimir Kulakov criticized Cherdyntsev's findings on the grounds that some of the properties Cherdyntsev claimed sergenium had, were inconsistent with then-current nuclear physics. The chief questions Kulakov raised were that the claimed alpha decay energy of sergenium was many orders of magnitude lower than expected and the half-life given was eight orders of magnitude shorter than what would be predicted for a nuclide alpha-decaying with the claimed decay energy. At the same time, a corrected half-life in the region of 10{{sup|16}}{{spaces}}years would be impossible because it would imply the samples contained ~100 milligrams of sergenium.{{cite journal|last1=Kulakov|first1=V. M.|date=1970|title=Has element 108 been discovered?|journal=Soviet Atomic Energy|volume=29|issue=5 |pages=1166–1168|doi=10.1007/BF01666716|s2cid=95772762}} In 2003, it was suggested that the observed alpha decay with energy 4.5{{spaces}}MeV could be due to a low-energy and strongly enhanced transition between different hyperdeformed states of a hassium isotope around {{sup|271}}Hs, thus suggesting that the existence of superheavy elements in nature was at least possible, but unlikely.{{cite journal |last1=Marinov |first1=A. |author-link=Amnon Marinov |last2=Gelberg |first2=S. |last3=Kolb |first3=D. |last4=Brandt |first4=R. |last5=Pape |first5=A. |display-authors=3 |title=New outlook on the possible existence of superheavy elements in nature |journal=Physics of Atomic Nuclei |volume=66 |issue=6 |pages=1137–1145 |doi=10.1134/1.1586428 |arxiv = nucl-ex/0210039 |bibcode = 2003PAN....66.1137M |year=2003|s2cid=119524738}}

In 2006, Russian geologist Alexei Ivanov hypothesized that an isomer of {{sup|271}}Hs might have a half-life of ~{{val|2.5e8|0.5}} years, which would explain the observation of alpha particles with energies of ~4.4{{spaces}}MeV in some samples of molybdenite and osmiridium. This isomer of {{sup|271}}Hs could be produced from the beta decay of {{sup|271}}Bh and {{sup|271}}Sg, which, being homologous to rhenium and molybdenum respectively, should occur in molybdenite along with rhenium and molybdenum if they occurred in nature. Because hassium is homologous to osmium, it should occur along with osmium in osmiridium if it occurs in nature. The decay chains of {{sup|271}}Bh and {{sup|271}}Sg are hypothetical and the predicted half-life of this hypothetical hassium isomer is not long enough for any sufficient quantity to remain on Earth. It is possible that more {{sup|271}}Hs may be deposited on the Earth as the Solar System travels through the spiral arms of the Milky Way; this would explain excesses of plutonium-239 found on the ocean floors of the Pacific Ocean and the Gulf of Finland. However, minerals enriched with {{sup|271}}Hs are predicted to have excesses of its daughters uranium-235 and lead-207; they would also have different proportions of elements that are formed by spontaneous fission, such as krypton, zirconium, and xenon. The natural occurrence of hassium in minerals such as molybdenite and osmiride is theoretically possible, but very unlikely.{{cite journal|last1=Ivanov|first1=A. V.|title=The possible existence of Hs in nature from a geochemical point of view|journal=Physics of Particles and Nuclei Letters|volume=3|pages=165–168|date=2006|doi=10.1134/S1547477106030046|issue=3|arxiv = nucl-th/0604052 |bibcode = 2006PPNL....3..165I |s2cid=118908703}}

In 2004, JINR started a search for natural hassium in the Modane Underground Laboratory in Modane, Auvergne-Rhône-Alpes, France; this was done underground to avoid interference and false positives from cosmic rays. In 2008–09, an experiment run in the laboratory resulted in detection of several registered events of neutron multiplicity (number of emitted free neutrons after a nucleus is hit by a neutron and fissioned) above three in natural osmium, and in 2012–13, these findings were reaffirmed in another experiment run in the laboratory. These results hinted natural hassium could potentially exist in nature in amounts that allow its detection by the means of analytical chemistry, but this conclusion is based on an explicit assumption that there is a long-lived hassium isotope to which the registered events could be attributed.{{cite report|url=https://fdocuments.net/document/joule-activity-report.html|title=Report on JINR activities and tasks accomplished in 2013 in Laboratoire Souterrain de Modane|editor-last=Yakushev|editor-first=E.|date=2013|last=Sokol|first=E.|publisher=Joint Institute for Nuclear Research|access-date=2020-07-10|archive-date=10 July 2020|archive-url=https://web.archive.org/web/20200710131658/https://fdocuments.net/document/joule-activity-report.html|url-status=live}}

Since {{sup|292}}Hs may be particularly stable against alpha decay and spontaneous fission, it was considered as a candidate to exist in nature. This nuclide, however, is predicted to be very unstable toward beta decay and any beta-stable isotopes of hassium such as {{sup|286}}Hs would be too unstable in the other decay channels to be observed in nature.{{cite journal |last=Oganessian|first=Yu.|title=Heaviest nuclei from {{sup|48}}Ca-induced reactions|date=2007 |journal=Journal of Physics G: Nuclear and Particle Physics|volume=34|issue=4|page=R235|doi=10.1088/0954-3899/34/4/R01|bibcode=2007JPhG...34R.165O |url=https://www.nucleonica.com/wiki/images/4/41/Oganessian.pdf |access-date=28 December 2018 |url-status=live|archive-date=9 August 2017|archive-url=https://web.archive.org/web/20170809112113/https://www.nucleonica.com/wiki/images/4/41/Oganessian.pdf}} A 2012 search for {{sup|292}}Hs in nature along with its homologue osmium at the Maier-Leibnitz Laboratory in Garching, Bavaria, Germany, was unsuccessful, setting an upper limit to its abundance at {{val|3|e=-15|u=grams}} of hassium per gram of osmium.{{cite journal|last1=Ludwig|first1=P. |last2=Faestermann|first2=T.|last3=Korschinek|first3=G.|last4=Rugel|first4=G.|last5=Dillmann|first5=I. |last6=Fimiani|first6=L.|last7=Bishop|first7=S.|last8=Kumar|first8=P.|display-authors=3 |title=Search for superheavy elements with 292 ≤ A ≤ 310 in nature with accelerator mass spectrometry|date=2012 |journal=Physical Review C|volume=85|issue=2|pages=024315{{hyphen}}1–024315{{hyphen}}8 |doi=10.1103/PhysRevC.85.024315 |url=https://www.nucastro.ph.tum.de/fileadmin/tuphena/www/pubs/e024315.pdf |access-date=28 December 2018|archive-url=https://web.archive.org/web/20181228223425/https://www.nucastro.ph.tum.de/fileadmin/tuphena/www/pubs/e024315.pdf |archive-date=28 December 2018|url-status=live}}

Predicted properties

Various calculations suggest hassium should be the heaviest group 8 element so far, consistently with the periodic law. Its properties should generally match those expected for a heavier homologue of osmium; as is the case for all transactinides, a few deviations are expected to arise from relativistic effects.{{sfn|Hoffman|Lee|Pershina|2006|pp=1666–1669}}

Very few properties of hassium or its compounds have been measured; this is due to its extremely limited and expensive production{{Cite news|last=Subramanian|first=S.|authorlink=Samanth Subramanian|url=https://www.bloomberg.com/news/features/2019-08-28/making-new-elements-doesn-t-pay-just-ask-this-berkeley-scientist|title=Making New Elements Doesn't Pay. Just Ask This Berkeley Scientist|website=Bloomberg Businessweek|date=28 August 2019|access-date=2020-01-18|archive-date=14 November 2020|archive-url=https://archive.today/20201114183428/https://www.bloomberg.com/news/features/2019-08-28/making-new-elements-doesn-t-pay-just-ask-this-berkeley-scientist|url-status=live}} and the fact that hassium (and its parents) decays very quickly. A few singular chemistry-related properties have been measured, such as enthalpy of adsorption of hassium tetroxide, but properties of hassium metal remain unknown and only predictions are available.

= Relativistic effects =

File:Energy levels of outermost orbitals of Hs and Os.jpgs, with and without taking relativistic effects into account. Note the lack of spin–orbit splitting (and thus the lack of distinction between d{{sub|3/2}} and d{{sub|5/2}} orbitals) in nonrelativistic calculations.]]

Relativistic effects in hassium should arise due to the high charge of its nuclei, which causes the electrons around the nucleus to move faster—so fast their speed is comparable to the speed of light.{{sfn|Hoffman|Lee|Pershina|2006|p=1666}} There are three main effects: the direct relativistic effect, the indirect relativistic effect, and spin–orbit splitting. (The existing calculations do not account for Breit interactions, but those are negligible, and their omission can only result in an uncertainty of the current calculations of no more than 2%.){{sfn|Hoffman|Lee|Pershina|2006|p=1669}}

As atomic number increases, so does the electrostatic attraction between an electron and the nucleus. This causes the velocity of the electron to increase, which leads to an increase in its mass. This in turn leads to contraction of the atomic orbitals, most specifically the s and p{{sub|1/2}} orbitals. Their electrons become more closely attached to the atom and harder to pull from the nucleus. This is the direct relativistic effect. It was originally thought to be strong only for the innermost electrons, but was later established to significantly influence valence electrons as well.{{sfn|Hoffman|Lee|Pershina|2006|pp=1666–1667}}

Since the s and p{{sub|1/2}} orbitals are closer to the nucleus, they take a bigger portion of the electric charge of the nucleus on themselves ("shield" it). This leaves less charge for attraction of the remaining electrons, whose orbitals therefore expand, making them easier to pull from the nucleus. This is the indirect relativistic effect.{{sfn|Hoffman|Lee|Pershina|2006|p=1667–1668}} As a result of the combination of the direct and indirect relativistic effects, the Hs{{sup|+}} ion, compared to the neutral atom, lacks a 6d electron, rather than a 7s electron. In comparison, Os{{sup|+}} lacks a 6s electron compared to the neutral atom.{{sfn|Hoffman|Lee|Pershina|2006|p=1672}} The ionic radius (in oxidation state +8) of hassium is greater than that of osmium because of the relativistic expansion of the 6p{{sub|3/2}} orbitals, which are the outermost orbitals for an Hs{{sup|8+}} ion (although in practice such highly charged ions would be too polarized in chemical environments to have much reality).{{sfn|Hoffman|Lee|Pershina|2006|p=1676}}

There are several kinds of electron orbitals, denoted s, p, d, and f (g orbitals are expected to start being chemically active among elements after element 120). Each of these corresponds to an azimuthal quantum number l: s to 0, p to 1, d to 2, and f to 3. Every electron also corresponds to a spin quantum number s, which may equal either +1/2 or −1/2.{{Cite web|url=http://www.xpsfitting.com/2012/08/spin-orbit-splitting.html|title=Spin Orbit Splitting|date=2012|website=X-ray Photoelectron Spectroscopy (XPS) Reference Pages|publisher=University of Western Ontario|access-date=2020-01-26|archive-date=25 January 2020|archive-url=https://web.archive.org/web/20200125152012/http://www.xpsfitting.com/2012/08/spin-orbit-splitting.html|url-status=live}} Thus, the total angular momentum quantum number j = l + s is equal to j = l ± 1/2 (except for l = 0, for which for both electrons in each orbital j = 0 + 1/2 = 1/2). Spin of an electron relativistically interacts with its orbit, and this interaction leads to a split of a subshell into two with different energies (the one with j = l − 1/2 is lower in energy and thus these electrons more difficult to extract):{{cite book|last=Thayer|first=J. S.|chapter=Relativistic effects and the chemistry of the heavier main group elements|date=2010|title=Relativistic Methods for Chemists|volume=10|page=65|editor-last=Barysz|editor-first=M.|publisher=Springer Netherlands|doi=10.1007/978-1-4020-9975-5_2|isbn=978-1-4020-9974-8|editor2-last=Ishikawa|editor2-first=Ya.|series=Challenges and Advances in Computational Chemistry and Physics}} for instance, of the six 6p electrons, two become 6p{{sub|1/2}} and four become 6p{{sub|3/2}}. This is the spin–orbit splitting (also called subshell splitting or jj coupling).{{sfn|Hoffman|Lee|Pershina|2006|pp=1668–1669}}{{Efn|The spin–orbit interaction is the interaction between the magnetic field caused by the spin of an electron and the effective magnetic field caused by the electric field of a nucleus and movement of an electron orbiting it. (According to the special theory of relativity, electric and magnetic fields are both occurrences of common electromagnetic fields that can be seen as more or less electric and more or less magnetic depending on the reference frame. The effective magnetic field from the reference frame of the electron is obtained from the nucleus's electric field after a relativistic transformation from the reference frame of the nucleus.) The splitting occurs because depending on the spin of an electron, it may be either attracted to or repealed by the nucleus; this attraction or repulsion is significantly weaker the electrostatic attraction between them and it can thus only somewhat affect the electron overall.{{Cite journal|last1=Spavieri|first1=G.|last2=Mansuripur|first2=M.|date=2015|title=Origin of the spin–orbit interaction|journal=Physica Scripta|volume=90|issue=8|pages=085501-1–085501-2|doi=10.1088/0031-8949/90/8/085501|issn=0031-8949|arxiv=1506.07239|bibcode=2015PhyS...90h5501S|s2cid=119196998}}}} It is most visible with p electrons,{{sfn|Hoffman|Lee|Pershina|2006|p=1669}} which do not play an important role in the chemistry of hassium,{{sfn|Hoffman|Lee|Pershina|2006|p=1673}} but those for d and f electrons are within the same order of magnitude{{sfn|Hoffman|Lee|Pershina|2006|p=1669}} (quantitatively, spin–orbit splitting in expressed in energy units, such as electronvolts).

These relativistic effects are responsible for the expected increase of the ionization energy, decrease of the electron affinity, and increase of stability of the +8 oxidation state compared to osmium; without them, the trends would be reversed.{{sfn|Hoffman|Lee|Pershina|2006|p=1679}} Relativistic effects decrease the atomization energies of hassium compounds because the spin–orbit splitting of the d orbital lowers binding energy between electrons and the nucleus and because relativistic effects decrease ionic character in bonding.{{sfn|Hoffman|Lee|Pershina|2006|p=1679}}

= Physical and atomic =

The previous members of group{{spaces}}8 have high melting points: Fe, 1538°C; Ru, 2334°C; Os, 3033°C. Like them, hassium is predicted to be a solid at room temperature though its melting point has not been precisely calculated. Hassium should crystallize in the hexagonal close-packed structure ({{sup|c}}/{{sub|a}}{{spaces}}={{spaces}}1.59), similarly to its lighter congener osmium. Pure metallic hassium is calculated{{cite journal |last1=Grossman |first1=J. C. |last2=Mizel |first2=A. |last3=Côté |first3=M. |last4=Cohen |first4=M. L. |last5=Louie |first5=S. G. |date=1999 |title=Transition metals and their carbides and nitrides: Trends in electronic and structural properties |journal=Phys. Rev. B |volume=60 |issue=9 |page=6344 |doi=10.1103/PhysRevB.60.6343 |bibcode=1999PhRvB..60.6343G |s2cid=18736376 |display-authors=3 }} to have a bulk modulus (resistance to uniform compression) of 450{{spaces}}GPa, comparable with that of diamond, 442{{spaces}}GPa.{{cite journal|last1=Cohen|first1=M. |journal=Physical Review B |volume=32|issue=12|pages=7988–7991|date=1985 |title=Calculation of bulk moduli of diamond and zinc-blende solids|doi=10.1103/PhysRevB.32.7988|pmid=9936971|bibcode=1985PhRvB..32.7988C}} Hassium is expected to be one of the densest of the 118 known elements, with a predicted density of 27–29 g/cm{{sup|3}} vs. the 22.59 g/cm{{sup|3}} measured for osmium.

Hassium's atomic radius is expected to be ≈126{{spaces}}pm.{{sfn|Hoffman|Lee|Pershina|2006|p=1691}} Due to relativistic stabilization of the 7s orbital and destabilization of the 6d orbital, the Hs{{sup|+}} ion is predicted to have an electron configuration of [Rn]{{spaces}}5f{{sup|14}}{{spaces}}6d{{sup|5}}{{spaces}}7s{{sup|2}}, giving up a 6d electron instead of a 7s electron, which is the opposite of the behaviour of its lighter homologues. The Hs{{sup|2+}} ion is expected to have electron configuration [Rn]{{spaces}}5f{{sup|14}}{{spaces}}6d{{sup|5}}{{spaces}}7s{{sup|1}}, analogous to that calculated for the Os{{sup|2+}} ion.{{sfn|Hoffman|Lee|Pershina|2006|p=1672}} In chemical compounds, hassium is calculated to display bonding characteristic for a d-block element, whose bonding will be primarily executed by 6d{{sub|3/2}} and 6d{{sub|5/2}} orbitals; compared to the elements from the previous periods, 7s, 6p{{sub|1/2}}, 6p{{sub|3/2}}, and 7p{{sub|1/2}} orbitals should be more important.{{sfn|Hoffman|Lee|Pershina|2006|p=1677}}

= Chemical =

class="wikitable" \|+Stable oxidation states in group 8{{sfn\|Greenwood\|Earnshaw\|1997\|pp=27–28}} ! Element !colspan="8"\| Stable oxidation states
iron		{{spaces}}{{spaces}}{{spaces}}{{spaces}}	+6			+3	+2
ruthenium	+8		+6	+5	+4	+3	+2
osmium	+8		+6	+5	+4	+3	+2

Hassium is the sixth member of the 6d series of transition metals and is expected to be much like the platinum group metals.{{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}} Some of these properties were confirmed by gas-phase chemistry experiments.{{cite report|last1=Düllmann|first1=C. E.|date=2011 |url=http://www.yumpu.com/en/document/view/7293741/superheavy-element-research-superheavy-element-research |title=Superheavy Element Research Superheavy Element—News from GSI and Mainz |publisher=University Mainz |access-date=30 June 2019 |archive-url=https://web.archive.org/web/20181223030058/https://www.yumpu.com/en/document/view/7293741/superheavy-element-research-superheavy-element-research |archive-date=23 December 2018 |url-status=live}}{{cite journal|last1=Düllmann|first1=C. E.|last2=Dressler|first2=R.|last3=Eichler|first3=B. |last4=Gäggeler |first4=H. W. |last5=Glaus |first5=F. |last6=Jost |first6=D. T. |last7=Piguet |first7=D. |last8=Soverna |first8=S. |last9=Türler |first9=A. |last10=Brüchle |first10=W. |last11=Eichler |first11=R. |last12=Jäger |first12=E. |last13=Pershina |first13=V. |last14=Schädel |first14=M. |last15=Schausten |first15=B. |last16=Schimpf |first16=E. |last17=Schött |first17=H.-J. |last18=Wirth |first18=G. |last19=Eberhardt |first19=K. |last20=Thörle |first20=P. |last21=Trautmann |first21=N. |last22=Ginter |first22=T. N. |last23=Gregorich|first23=K. E.|last24=Hoffman|first24=D. C.|last25=Kirbach|first25=U. W. |last26=Lee |first26=D. M. |last27=Nitsche |first27=H. |last28=Patin |first28=J. B. |last29=Sudowe |first29=R. |last30=Zielinski|first30=P. M. |last31=Timokhin|first31=S. N.|last32=Yakushev|first32=A. B. |last33=Vahle |first33=A. |last34=Qin |first34=Z. |display-authors=3 |date=2003 |title=First chemical investigation of hassium (Hs, Z=108) |journal=Czechoslovak Journal of Physics |volume=53 |issue=1 Supplement |pages=A291–A298 |doi=10.1007/s10582-003-0037-4 |bibcode = 2003CzJPS..53A.291D|s2cid=123402972 }}{{Cite web |url=http://www.gsi.de/documents/DOC-2003-Jun-29-2.pdf |title=Chemistry of Hassium|date=2002|publisher=Gesellschaft für Schwerionenforschung|archive-url=https://web.archive.org/web/20120311001032/http://www.gsi.de/documents/DOC-2003-Jun-29-2.pdf|archive-date=2012-03-11|access-date=2019-06-30}} The group{{spaces}}8 elements portray a wide variety of oxidation states but ruthenium and osmium readily portray their group oxidation state of +8; this state becomes more stable down the group.{{sfn|Greenwood|Earnshaw|1997|pp=27–28}}{{cite journal|title=Oxidation States of Ruthenium and Osmium|date=2004 |last1=Barnard|first1=C. F. J.|last2=Bennett|first2=S. C.|journal=Platinum Metals Review|volume=48 |issue=4|pages=157–158|doi=10.1595/147106704X10801|doi-access=free}} This oxidation state is extremely rare: among stable elements, only ruthenium, osmium, and xenon are able to attain it in reasonably stable compounds.{{efn|While iridium is known to show a +8 state in iridium tetroxide, as well as a unique +9 state in the iridium tetroxide cation {{chem|IrO|4|+}}, the former is known only in matrix isolation and the latter in the gas phase, and no iridium compounds in such high oxidation states have been synthesized in macroscopic amounts.{{cite journal|doi=10.1002/anie.200902733 |pmid=19593837 |title=Formation and Characterization of the Iridium Tetroxide Molecule with Iridium in the Oxidation State +VIII |year=2009|last1=Gong|first1=Yu|last2=Zhou|first2=M.|last3=Kaupp|first3=M.|last4=Riedel|first4=S.|journal=Angewandte Chemie International Edition|volume=48 |issue=42|pages=7879–7883}}{{cite journal |last1=Wang |first1=G. |last2=Zhou |first2=M. |last3=Goettel |first3=J. T. |last4=Schrobilgen |first4=G. G. |last5=Su |first5=J. |last6=Li |first6=J. |last7=Schlöder |first7=T. |last8=Riedel |first8=S. |display-authors=3 |date=2014 |title=Identification of an iridium-containing compound with a formal oxidation state of IX |journal=Nature |volume=514 |issue=7523 |pages=475–477 |doi=10.1038/nature13795 |pmid=25341786 |bibcode=2014Natur.514..475W|s2cid=4463905}}}} Hassium is expected to follow its congeners and have a stable +8 state, but like them it should show lower stable oxidation states such as +6, +4, +3, and +2.{{sfn|Hoffman|Lee|Pershina|2006|p=1691}} Hassium(IV) is expected to be more stable than hassium(VIII) in aqueous solution.{{sfn|Hoffman|Lee|Pershina|2006|p=1720}} Hassium should be a rather noble metal.{{cite journal |last1=Nagame |first1=Yu. |last2=Kratz |first2=J. V. |last3=Schädel |first3=M. |date=2015 |title=Chemical studies of elements with Z ≥ 104 in liquid phase |journal=Nuclear Physics A |volume=944 |page=632 |doi=10.1016/j.nuclphysa.2015.07.013 |bibcode=2015NuPhA.944..614N |url=https://jopss.jaea.go.jp/search/servlet/search?5050598 |access-date=24 September 2019 |archive-date=12 December 2022 |archive-url=https://web.archive.org/web/20221212184356/https://jopss.jaea.go.jp/search/servlet/search?5050598 |url-status=live }} The standard reduction potential for the Hs⁴⁺/Hs couple is expected to be 0.4{{spaces}}V.{{sfn|Hoffman|Lee|Pershina|2006|p=1691}}

The group 8 elements show a distinctive oxide chemistry. All the lighter members have known or hypothetical tetroxides, MO{{sub|4}}.{{cite journal|title=Higher Oxidation States of Iron in Solid State: Synthesis and Their Mössbauer Characterization—Ferrates—ACS Symposium Series (ACS Publications)|date=2008|first1=Yu. D. |last1=Perfiliev|first2=V. K.|last2=Sharma|volume=48|issue=4 |pages=157–158|journal=Platinum Metals Review |doi=10.1595/147106704X10801|doi-access=free}} Their oxidizing power decreases as one descends the group. FeO{{sub|4}} is not known due to its extraordinarily large electron affinity—the amount of energy released when an electron is added to a neutral atom or molecule to form a negative ion{{cite journal|title=electron affinity, E{{sub|ea}}|date=2009|url=http://goldbook.iupac.org/E01977.html|journal=IUPAC Compendium of Chemical Terminology|editor-last=Nič|editor-first=M.|edition=2.1.0|publisher=International Union of Pure and Applied Chemistry|doi=10.1351/goldbook.e01977|isbn=978-0-9678550-9-7|access-date=2019-11-24|editor2-last=Jirát|editor2-first=J.|editor3-last=Košata|editor3-first=B.|editor4-last=Jenkins|editor4-first=A.|doi-access=free|archive-date=31 August 2014|archive-url=https://web.archive.org/web/20140831071649/http://goldbook.iupac.org/E01977.html|url-status=live}}—which results in the formation of the well-known oxyanion ferrate(VI), {{chem|FeO|4|2-}}.{{Cite journal|title=FeO₄: A unique example of a closed-shell cluster mimicking a superhalogen|doi=10.1103/PhysRevA.59.3681|date=1999|last1=Gutsev|first1=G. L.|last2=Khanna |first2=S.|last3=Rao|first3=B.|last4=Jena|first4=P. |journal=Physical Review A|volume=59|issue=5 |pages=3681–3684|bibcode=1999PhRvA..59.3681G}} Ruthenium tetroxide, RuO₄, which is formed by oxidation of ruthenium(VI) in acid, readily undergoes reduction to ruthenate(VI), {{chem|RuO|4|2-}}.{{cite book |last1= Cotton|first1=S. A.|title= Chemistry of Precious Metals|date= 1997|publisher= Chapman and Hall|isbn= 978-0-7514-0413-5}}{{Cite book |last1=Martín |first1=V. S. |last2=Palazón |first2=J. M. |last3=Rodríguez |first3=C. M. |last4=Nevill |first4=C. R. |chapter=Ruthenium(VIII) Oxide |doi=10.1002/047084289X.rr009.pub2 |title=Encyclopedia of Reagents for Organic Synthesis |year=2006 |isbn=978-0471936237}} Oxidation of ruthenium metal in air forms the dioxide, RuO₂.{{cite journal |first1=G. M. |last1=Brown |first2=J. H. |last2=Butler |date=1997 |title=New method for the characterization of domain morphology of polymer blends using ruthenium tetroxide staining and low voltage scanning electron microscopy (LVSEM) |journal=Polymer |volume=38 |issue=15 |pages=3937–3945 |doi=10.1016/S0032-3861(96)00962-7}} In contrast, osmium burns to form the stable tetroxide, OsO₄,{{cite book|title=Encyclopaedia of Occupational Health and Safety|last=Stellman|first=J. M. |chapter=Osmium |isbn=978-92-2-109816-4|date=1998 |publisher=International Labour Organization|pages=63.34|chapter-url=https://books.google.com/books?id=nDhpLa1rl44C|oclc=35279504 |url=https://archive.org/details/encyclopaediaofo0003unse|url-access=registration}}{{Housecroft2nd|pages=671–673, 710}} which complexes with the hydroxide ion to form an osmium(VIII) -ate complex, [OsO₄(OH)₂]²⁻.{{cite web |author=Thompson, M. |publisher=Bristol University |title=Osmium tetroxide (OsO₄) |url=http://www.chm.bris.ac.uk/motm/oso4/oso4h.htm |access-date=2012-04-07 |archive-url=https://web.archive.org/web/20130922133517/http://www.chm.bris.ac.uk/motm/oso4/oso4h.htm |archive-date=22 September 2013 |url-status=live}} Therefore, hassium should behave as a heavier homologue of osmium by forming of a stable, very volatile tetroxide HsO₄,{{cite book |title=The Chemistry of Superheavy Elements |first=M. |last=Schädel |publisher=Springer |date=2003 |isbn=978-1402012501 |page=269 |access-date=17 November 2012 |url=https://books.google.com/books?id=3ItA4fExU7wC |archive-date=8 October 2024 |archive-url=https://web.archive.org/web/20241008102909/https://books.google.com/books?id=3ItA4fExU7wC |url-status=live }}{{sfn|Hoffman|Lee|Pershina|2006|p=1685}} which undergoes complexation with hydroxide to form a hassate(VIII), [HsO₄(OH)₂]²⁻. Ruthenium tetroxide and osmium tetroxide are both volatile due to their symmetrical tetrahedral molecular geometry and because they are charge-neutral; hassium tetroxide should similarly be a very volatile solid. The trend of the volatilities of the group{{spaces}}8 tetroxides is experimentally known to be RuO₄{{spaces}}<{{spaces}}OsO₄{{spaces}}>{{spaces}}HsO₄, which confirms the calculated results. In particular, the calculated enthalpies of adsorption—the energy required for the adhesion of atoms, molecules, or ions from a gas, liquid, or dissolved solid to a surface—of HsO₄, −(45.4{{spaces}}±{{spaces}}1){{spaces}}kJ/mol on quartz, agrees very well with the experimental value of −(46{{spaces}}±{{spaces}}2){{spaces}}kJ/mol.{{cite journal |last1=Pershina |first1=V. |last2=Anton |first2=J. |last3=Jacob |first3=T. |date=2008 |title=Fully relativistic density-functional-theory calculations of the electronic structures of MO₄ (M = Ru, Os, and element 108, Hs) and prediction of physisorption |journal=Physical Review A |volume=78 |issue=3 |pages=032518 |doi=10.1103/PhysRevA.78.032518|bibcode=2008PhRvA..78c2518P }}

Experimental chemistry

{{multiple image

| align = left

| direction = vertical

| header =

| width = 180

| image1 = Ferrocene-from-xtal-3D-balls.png

| alt1 = Ball-and-stick model of ferrocene molecule

| caption1 = In ferrocene, the cyclopentadienyl rings are in a staggered conformation.

| image2 = Ruthenocene-from-xtal-3D-balls.png

| alt2 = Ball-and-stick model of ruthenocene molecule

| caption2 = In ruthenocene and osmocene, the cyclopentadienyl rings are in an eclipsed conformation. Hassocene is also predicted to have this structure.

}}

The first goal for chemical investigation was the formation of the tetroxide; it was chosen because ruthenium and osmium form volatile tetroxides, being the only transition metals to display a stable compound in the +8 oxidation state.{{Cite journal|last=Schädel|first=M.|date=2006|title=Chemistry of Superheavy Elements|journal=Angewandte Chemie International Edition|volume=45|issue=3|page=391|doi=10.1002/anie.200461072|pmid=16365916|issn=1433-7851|url=https://cds.cern.ch/record/643991|access-date=21 June 2023|archive-date=17 April 2021|archive-url=https://web.archive.org/web/20210417211550/http://cds.cern.ch/record/643991|url-status=live}} Despite this selection for gas-phase chemical studies being clear from the beginning, chemical characterization of hassium was considered a difficult task for a long time. Although hassium was first synthesized in 1984, it was not until 1996 that a hassium isotope long-lived enough to allow chemical studies was synthesized. Unfortunately, this isotope, {{sup|269}}Hs, was synthesized indirectly from the decay of {{sup|277}}Cn; not only are indirect synthesis methods not favourable for chemical studies,{{sfn|Hoffman|Lee|Pershina|2006|p=1719}} but the reaction that produced the isotope {{sup|277}}Cn had a low yield—its cross section was only 1{{spaces}}pb—and thus did not provide enough hassium atoms for a chemical investigation. Direct synthesis of {{sup|269}}Hs and {{sup|270}}Hs in the reaction {{sup|248}}Cm({{sup|26}}Mg,xn){{sup|274−x}}Hs (x{{spaces}}={{spaces}}4 or 5) appeared more promising because the cross section for this reaction was somewhat larger at 7{{spaces}}pb. This yield was still around ten times lower than that for the reaction used for the chemical characterization of bohrium. New techniques for irradiation, separation, and detection had to be introduced before hassium could be successfully characterized chemically.

Ruthenium and osmium have very similar chemistry due to the lanthanide contraction but iron shows some differences from them; for example, although ruthenium and osmium form stable tetroxides in which the metal is in the +8 oxidation state, iron does not. In preparation for the chemical characterization of hassium, research focused on ruthenium and osmium rather than iron because hassium was expected to be similar to ruthenium and osmium, as the predicted data on hassium closely matched that of those two.{{cite journal |last1=Düllmann|first1=C. E.|last2=Brüchle|first2=W. |last3=Dressler|first3=R.|last4=Eberhardt|first4=K. |last5=Eichler|first5=B.|last6=Eichler|first6=R.|last7=Gäggeler|first7=H. W.|last8=Ginter|first8=T. N. |last9=Glaus|first9=F.|display-authors=3|date=2002|title=Chemical investigation of hassium (element 108) |journal=Nature|volume=418|issue=6900|pages=859–862|bibcode=2002Natur.418..859D |doi=10.1038/nature00980|pmid=12192405|first10=K. E.|last10=Gregorich|first11=D. C. |last11=Hoffman |first12=E.|last12=Jäger|first13=D. T.|last13=Jost|first14=U. W.|last14=Kirbach|first15=D. M.|last15=Lee |first16=H.|last16=Nitsche|first17=J. B.|last17=Patin|first18=V.|last18=Pershina|first19=D.|last19=Piguet |first20=Z.|last20=Qin|first21=M.|last21=Schädel|first22=B.|last22=Schausten|first23=E.|last23=Schimpf |first24=H.-J.|last24=Schött|first25=S.|last25=Soverna|first26=R.|last26=Sudowe|first27=P.|last27=Thörle |first28=S. N. |last28=Timokhin|first29=N.|last29=Trautmann|first30=A.|last30=Türler|first31=A. |last31=Vahle|first32=G.|last32=Wirth|first33=A. B.|last33=Yakushev|first34=P. M.|last34=Zielinski |s2cid=4412944}}{{Cite journal |last1=Düllmann|first1=C. E.|last2=Eichler|first2=B. |last3=Eichler|first3=R.|last4=Gäggeler|first4=H. W.|last5=Türler|first5=A.|display-authors=3|date=2002 |title=On the Stability and Volatility of Group 8 Tetroxides, MO{{sub|4}} (M = Ruthenium, Osmium, and Hassium (Z = 108)) |journal=The Journal of Physical Chemistry B|volume=106|issue=26|pages=6679–6680 |doi=10.1021/jp0257146|issn=1520-6106}}

The first chemistry experiments were performed using gas thermochromatography in 2001, using the synthetic osmium radioisotopes {{sup|172, 173}}Os as a reference. During the experiment, seven hassium atoms were synthesized using the reactions {{sup|248}}Cm({{sup|26}}Mg,5n){{sup|269}}Hs and {{sup|248}}Cm({{sup|26}}Mg,4n){{sup|270}}Hs. They were then thermalized and oxidized in a mixture of helium and oxygen gases to form hassium tetroxide molecules.{{sfn|Hoffman|Lee|Pershina|2006|pp=1712–1714}}

:Hs + 2 O{{sub|2}} → HsO{{sub|4}}

The measured deposition temperature of hassium tetroxide was higher than that of osmium tetroxide, which indicated the former was the less volatile one, and this placed hassium firmly in group 8.{{sfn|Hoffman|Lee|Pershina|2006|pp=1714–1715}} The enthalpy of adsorption for HsO{{sub|4}} measured, {{val|−46|2|u=kJ/mol}}, was significantly lower than the predicted value, {{val|−36.7|1.5|u=kJ/mol}}, indicating OsO{{sub|4}} is more volatile than HsO{{sub|4}}, contradicting earlier calculations that implied they should have very similar volatilities. For comparison, the value for OsO{{sub|4}} is {{val|−39|1|u=kJ/mol}}.{{sfn|Hoffman|Lee|Pershina|2006|p=1714}} (The calculations that yielded a closer match to the experimental data came after the experiment, in 2008.) It is possible hassium tetroxide interacts differently with silicon nitride than with silicon dioxide, the chemicals used for the detector; further research is required to establish whether there is a difference between such interactions and whether it has influenced the measurements. Such research would include more accurate measurements of the nuclear properties of {{sup|269}}Hs and comparisons with RuO{{sub|4}} in addition to OsO{{sub|4}}.{{sfn|Hoffman|Lee|Pershina|2006|pp=1714–1715}}

In 2004, scientists reacted hassium tetroxide and sodium hydroxide to form sodium hassate(VIII), a reaction that is well known with osmium. This was the first acid-base reaction with a hassium compound, forming sodium hassate(VIII):{{cite book|first1=A.|last1=von Zweidorf|first2=R.|last2=Angert|first3=W.|last3=Brüchle|display-authors=et al.|year=2003|chapter=Final result of the CALLISTO-experiment: Formation of sodium hassate(VIII)|title=Advances in Nuclear and Radiochemistry|volume=3|url=https://www-windows.gsi.de/superheavies/english/publications/pub_images/pub_annual_img/annual_reports_2003/SHE_AR_2003_172.pdf|access-date=2019-06-13|publisher=Forschungszentrum Jülich|pages=141–143|isbn=978-3-89336-362-9|archive-date=29 July 2021|archive-url=https://web.archive.org/web/20210729084845/https://www-windows.gsi.de/superheavies/english/publications/pub_images/pub_annual_img/annual_reports_2003/SHE_AR_2003_172.pdf|url-status=dead}}

:{{chem|HsO|4}} + 2 NaOH → {{chem|Na|2|[HsO|4|(OH)|2|]}}

The team from the University of Mainz planned in 2008 to study the electrodeposition of hassium atoms using the new TASCA facility at GSI. Their aim was to use the reaction {{sup|226}}Ra({{sup|48}}Ca,4n){{sup|270}}Hs.{{cite web|url=https://www-win.gsi.de/tasca/workshops/tasca08/contributions/TASCA08_Cont_Kratz_2.pdf|archive-url=https://web.archive.org/web/20200311203404/https://www-win.gsi.de/tasca/workshops/tasca08/contributions/TASCA08_Cont_Kratz_2.pdf|url-status=dead|archive-date=11 March 2020|title=Electrodeposition experiments with hassium|date=2011|first1=J.|last1=Even|first2=J. V.|last2=Kratz|first3=M.|last3=Mendel|first4=N.|last4=Wiehl|publisher=Gesellschaft für Schwerionenforschung|access-date=30 June 2019}} Scientists at GSI were hoping to use TASCA to study the synthesis and properties of the hassium(II) compound hassocene, Hs(Cyclopentadienyl){{sub|2}}, using the reaction {{sup|226}}Ra({{sup|48}}Ca,xn). This compound is analogous to the lighter compounds ferrocene, ruthenocene, and osmocene, and is expected to have the two cyclopentadienyl rings in an eclipsed conformation like ruthenocene and osmocene and not in a staggered conformation like ferrocene.{{cite web |url=http://www-win.gsi.de/tasca08/contributions/TASCA08_Cont_Duellmann1.pdf |title=Investigation of group 8 metallocenes @ TASCA |last1=Düllmann |first1=Christoph E. |date=31 October 2008 |work=7th Workshop on Recoil Separator for Superheavy Element Chemistry TASCA 08 |publisher=Gesellschaft für Schwerionenforschung |accessdate=25 March 2013 |archive-date=5 March 2012 |archive-url=https://web.archive.org/web/20120305105102/http://www-win.gsi.de/tasca08/contributions/TASCA08_Cont_Duellmann1.pdf |url-status=dead }} Hassocene, which is expected to be a stable and highly volatile compound, was chosen because it has hassium in the low formal oxidation state of +2—although the bonding between the metal and the rings is mostly covalent in metallocenes—rather than the high +8 state that had previously been investigated, and relativistic effects were expected to be stronger in the lower oxidation state. The highly symmetrical structure of hassocene and its low number of atoms make relativistic calculations easier. {{As of|2021||df=}}, there are no experimental reports of hassocene.{{cite book |last1=Maria |first1=L. |last2=Marçalo |first2=J. |last3=Gibson |first3=J. K. |date=2019 |editor1-last=Evans |editor1-first=W. J. |editor2-last=Hanusa |editor2-first=T. P. |title=The Heaviest Metals: Science and Technology of the Actinides and Beyond |publisher=John Wiley & Sons |page=260 |isbn=978-1-119-30408-1}}

Notes

References

{{Reflist|30em|refs=

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