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Copernicium, 112Cn
Copernicium
Pronunciation/ˌkoʊpərˈnɪsiəm/ ​(KOH-pər-NISS-ee-əm)
Mass number[285]
Copernicium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Hg
↑
Cn
↓
—
roentgenium ← copernicium → nihonium
Atomic number (Z)112
Groupgroup 12
Periodperiod 7
Block  d-block
Electron configuration[Rn] 5f14 6d10 7s2 (predicted)[1]
Electrons per shell2, 8, 18, 32, 32, 18, 2 (predicted)
Physical properties
Phase at STPliquid (predicted)[2][3]
Melting point283 ± 11 K ​(10 ± 11 °C, ​50 ± 20 °F) (predicted)[3]
Boiling point340 ± 10 K ​(67 ± 10 °C, ​153 ± 18 °F)[3] (predicted)
Density (near r.t.)14.0 g/cm3 (predicted)[3]
Triple point283 K, ​25 kPa (predicted)[3]
Atomic properties
Oxidation statescommon: (none)
(+2), (+4)[1]
Ionization energies
  • 1st: 1155 kJ/mol
  • 2nd: 2170 kJ/mol
  • 3rd: 3160 kJ/mol
  • (more) (all estimated)[1]
Atomic radiuscalculated: 147 pm[1][4] (predicted)
Covalent radius122 pm (predicted)[5]
Other properties
Natural occurrencesynthetic
Crystal structure ​hexagonal close-packed (hcp)
Hexagonal close-packed crystal structure for copernicium

(predicted)[3]
CAS Number54084-26-3
History
Namingafter Nicolaus Copernicus
DiscoveryGesellschaft für Schwerionenforschung (1996)
Isotopes of copernicium
Main isotopes[6] Decay
abun­dance half-life (t1/2) mode pro­duct
283Cn synth 3.81 s[7] α96% 279Ds
SF4% –
ε? 283Rg
285Cn synth 30 s α 281Ds
286Cn synth 8.4 s? SF –
 Category: Copernicium
| references

Copernicium is a synthetic chemical element with the symbol Cn and atomic number 112. Its known isotopes are extremely radioactive, and have only been created in a laboratory. The most stable known isotope, copernicium-285, has a half-life of approximately 28 seconds. Copernicium was first created in 1996 by the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany. It was named after the astronomer Nicolaus Copernicus.

In the periodic table of the elements, copernicium is a d-block transactinide element and a group 12 element. During reactions with gold, it has been shown[8] to be an extremely volatile element, so much so that it is possibly a gas or a volatile liquid at standard temperature and pressure.

Copernicium is calculated to have several properties that differ from its lighter homologues in group 12, zinc, cadmium and mercury; due to relativistic effects, it may give up its 6d electrons instead of its 7s ones, and it may have more similarities to the noble gases such as radon rather than its group 12 homologues. Calculations indicate that copernicium may show the oxidation state +4, while mercury shows it in only one compound of disputed existence and zinc and cadmium do not show it at all. It has also been predicted to be more difficult to oxidize copernicium from its neutral state than the other group 12 elements. Predictions vary on whether solid copernicium would be a metal, semiconductor, or insulator. Copernicium is one of the heaviest elements whose chemical properties have been experimentally investigated.

Introduction

This section is transcluded from Introduction to the heaviest elements. (edit | history)
"Transactinide element" redirects here. Not to be confused with Transuranium element.
Superheavy elements
in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Z ≥ 104 (Rf)

Superheavy elements, also known as transactinide elements, transactinides, or super-heavy elements, or superheavies for short, are the chemical elements with atomic number greater than 104.[9] The superheavy elements are those beyond the actinides in the periodic table; the last actinide is lawrencium (atomic number 103). By definition, superheavy elements are also transuranium elements, i.e., having atomic numbers greater than that of uranium (92). Depending on the definition of group 3 adopted by authors, lawrencium may also be included to complete the 6d series.[10][11][12][13]

Glenn T. Seaborg first proposed the actinide concept, which led to the acceptance of the actinide series. He also proposed a transactinide series ranging from element 104 to 121 and a superactinide series approximately spanning elements 122 to 153 (though more recent work suggests the end of the superactinide series to occur at element 157 instead). The transactinide seaborgium was named in his honor.[14][15]

Superheavies are radioactive and have only been obtained synthetically in laboratories. No macroscopic sample of any of these elements has ever been produced. Superheavies are all named after physicists and chemists or important locations involved in the synthesis of the elements.

IUPAC defines an element to exist if its lifetime is longer than 10−14 seconds, which is the time it takes for the atom to form an electron cloud.[16]

The known superheavies form part of the 6d and 7p series in the periodic table. Except for rutherfordium and dubnium (and lawrencium if it is included), even the longest-lived known isotopes of superheavies have half-lives of minutes or less. The element naming controversy involved elements 102–109. Some of these elements thus used systematic names for many years after their discovery was confirmed. (Usually the systematic names are replaced with permanent names proposed by the discoverers relatively soon after a discovery has been confirmed.)

Introduction

Synthesis of superheavy nuclei

See also: Nucleosynthesis and Nuclear reaction
A graphic depiction of a nuclear fusion reaction
A graphic depiction of a nuclear fusion reaction. Two nuclei fuse into one, emitting a neutron. Reactions that created new elements to this moment were similar, with the only possible difference that several singular neutrons sometimes were released, or none at all.

A superheavy[a] atomic nucleus is created in a nuclear reaction that combines two other nuclei of unequal size[b] into one; roughly, the more unequal the two nuclei in terms of mass, the greater the possibility that the two react.[22] The material made of the heavier nuclei is made into a target, which is then bombarded by the beam of lighter nuclei. Two nuclei can only fuse into one if they approach each other closely enough; normally, nuclei (all positively charged) repel each other due to electrostatic repulsion. The strong interaction can overcome this repulsion but only within a very short distance from a nucleus; beam nuclei are thus greatly accelerated in order to make such repulsion insignificant compared to the velocity of the beam nucleus.[23] The energy applied to the beam nuclei to accelerate them can cause them to reach speeds as high as one-tenth of the speed of light. However, if too much energy is applied, the beam nucleus can fall apart.[23]

Coming close enough alone is not enough for two nuclei to fuse: when two nuclei approach each other, they usually remain together for about 10−20 seconds and then part ways (not necessarily in the same composition as before the reaction) rather than form a single nucleus.[23][24] This happens because during the attempted formation of a single nucleus, electrostatic repulsion tears apart the nucleus that is being formed.[23] Each pair of a target and a beam is characterized by its cross section—the probability that fusion will occur if two nuclei approach one another expressed in terms of the transverse area that the incident particle must hit in order for the fusion to occur.[c] This fusion may occur as a result of the quantum effect in which nuclei can tunnel through electrostatic repulsion. If the two nuclei can stay close past that phase, multiple nuclear interactions result in redistribution of energy and an energy equilibrium.[23]

External videos
video icon Visualization of unsuccessful nuclear fusion, based on calculations from the Australian National University[26]

The resulting merger is an excited state[27]—termed a compound nucleus—and thus it is very unstable.[23] To reach a more stable state, the temporary merger may fission without formation of a more stable nucleus.[28] Alternatively, the compound nucleus may eject a few neutrons, which would carry away the excitation energy; if the latter is not sufficient for a neutron expulsion, the merger would produce a gamma ray. This happens in about 10−16 seconds after the initial nuclear collision and results in creation of a more stable nucleus.[28] The definition by the IUPAC/IUPAP Joint Working Party (JWP) states that a chemical element can only be recognized as discovered if a nucleus of it has not decayed within 10−14 seconds. This value was chosen as an estimate of how long it takes a nucleus to acquire electrons and thus display its chemical properties.[29][d]

Decay and detection

See also: Gaseous ionization detector

The beam passes through the target and reaches the next chamber, the separator; if a new nucleus is produced, it is carried with this beam.[31] In the separator, the newly produced nucleus is separated from other nuclides (that of the original beam and any other reaction products)[e] and transferred to a surface-barrier detector, which stops the nucleus. The exact location of the upcoming impact on the detector is marked; also marked are its energy and the time of the arrival.[31] The transfer takes about 10−6 seconds; in order to be detected, the nucleus must survive this long.[34] The nucleus is recorded again once its decay is registered, and the location, the energy, and the time of the decay are measured.[31]

Stability of a nucleus is provided by the strong interaction. However, its range is very short; as nuclei become larger, its influence on the outermost nucleons (protons and neutrons) weakens. At the same time, the nucleus is torn apart by electrostatic repulsion between protons, and its range is not limited.[35] Total binding energy provided by the strong interaction increases linearly with the number of nucleons, whereas electrostatic repulsion increases with the square of the atomic number, i.e. the latter grows faster and becomes increasingly important for heavy and superheavy nuclei.[36][37] Superheavy nuclei are thus theoretically predicted[38] and have so far been observed[39] to predominantly decay via decay modes that are caused by such repulsion: alpha decay and spontaneous fission.[f] Almost all alpha emitters have over 210 nucleons,[41] and the lightest nuclide primarily undergoing spontaneous fission has 238.[42] In both decay modes, nuclei are inhibited from decaying by corresponding energy barriers for each mode, but they can be tunneled through.[36][37]

Apparatus for creation of superheavy elements
Scheme of an apparatus for creation of superheavy elements, based on the Dubna Gas-Filled Recoil Separator set up in the Flerov Laboratory of Nuclear Reactions 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.[43]

Alpha particles are commonly produced in radioactive decays because the mass of an alpha particle per nucleon is small enough to leave some energy for the alpha particle to be used as kinetic energy to leave the nucleus.[44] Spontaneous fission is caused by electrostatic repulsion tearing the nucleus apart and produces various nuclei in different instances of identical nuclei fissioning.[37] As the atomic number increases, spontaneous fission rapidly becomes more important: spontaneous fission partial half-lives decrease by 23 orders of magnitude from uranium (element 92) to nobelium (element 102),[45] and by 30 orders of magnitude from thorium (element 90) to fermium (element 100).[46] The earlier liquid drop model thus suggested that spontaneous fission would occur nearly instantly due to disappearance of the fission barrier for nuclei with about 280 nucleons.[37][47] The later nuclear shell model suggested that nuclei with about 300 nucleons would form an island of stability in which nuclei will be more resistant to spontaneous fission and will primarily undergo alpha decay with longer half-lives.[37][47] 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.[48] Experiments on lighter superheavy nuclei,[49] as well as those closer to the expected island,[45] have shown greater than previously anticipated stability against spontaneous fission, showing the importance of shell effects on nuclei.[g]

Alpha decays are registered by the emitted alpha particles, and the decay products are easy to determine before the actual decay; if such a decay or a series of consecutive decays produces a known nucleus, the original product of a reaction can be easily determined.[h] (That all decays within a decay chain were indeed related to each other is established by the location of these decays, which must be in the same place.)[31] The known nucleus can be recognized by the specific characteristics of decay it undergoes such as decay energy (or more specifically, the kinetic energy of the emitted particle).[i] Spontaneous fission, however, produces various nuclei as products, so the original nuclide cannot be determined from its daughters.[j]

The information available to physicists aiming to synthesize a superheavy element is thus the information collected at the detectors: location, energy, and time of arrival of a particle to the detector, and those of its decay. The physicists analyze this data and seek to conclude that it was indeed caused by a new element and could not have been caused by a different nuclide than the one claimed. Often, provided data is insufficient for a conclusion that a new element was definitely created and there is no other explanation for the observed effects; errors in interpreting data have been made.[k]

History

Early predictions

The heaviest element known at the end of the 19th century was uranium, with an atomic mass of about 240 (now known to be 238) amu. Accordingly, it was placed in the last row of the periodic table; this fueled speculation about the possible existence of elements heavier than uranium and why A = 240 seemed to be the limit. Following the discovery of the noble gases, beginning with argon in 1895, the possibility of heavier members of the group was considered. Danish chemist Julius Thomsen proposed in 1895 the existence of a sixth noble gas with Z = 86, A = 212 and a seventh with Z = 118, A = 292, the last closing a 32-element period containing thorium and uranium.[60] In 1913, Swedish physicist Johannes Rydberg extended Thomsen's extrapolation of the periodic table to include even heavier elements with atomic numbers up to 460, but he did not believe that these superheavy elements existed or occurred in nature.[61]

In 1914, German physicist Richard Swinne proposed that elements heavier than uranium, such as those around Z = 108, could be found in cosmic rays. He suggested that these elements may not necessarily have decreasing half-lives with increasing atomic number, leading to speculation about the possibility of some longer-lived elements at Z = 98–102 and Z = 108–110 (though separated by short-lived elements). Swinne published these predictions in 1926, believing that such elements might exist in Earth's core, iron meteorites, or the ice caps of Greenland where they had been locked up from their supposed cosmic origin.[62]

Discoveries

Work performed from 1961 to 2013 at four labs – Lawrence Berkeley National Laboratory in the US, the Joint Institute for Nuclear Research in the USSR (later Russia), the GSI Helmholtz Centre for Heavy Ion Research in Germany, and Riken in Japan – identified and confirmed the elements lawrencium to oganesson according to the criteria of the IUPAC–IUPAP Transfermium Working Groups and subsequent Joint Working Parties. These discoveries complete the seventh row of the periodic table. The next two elements, ununennium (Z = 119) and unbinilium (Z = 120), have not yet been synthesized. They would begin an eighth period.

List of elements

Characteristics

Due to their short half-lives (for example, the most stable known isotope of seaborgium has a half-life of 14 minutes, and half-lives decrease with increasing atomic number) and the low yield of the nuclear reactions that produce them, new methods have had to be created to determine their gas-phase and solution chemistry based on very small samples of a few atoms each. Relativistic effects become very important in this region of the periodic table, causing the filled 7s orbitals, empty 7p orbitals, and filling 6d orbitals to all contract inward toward the atomic nucleus. This causes a relativistic stabilization of the 7s electrons and makes the 7p orbitals accessible in low excitation states.[15]

Elements 103 to 112, lawrencium to copernicium, form the 6d series of transition elements. Experimental evidence shows that elements 103–108 behave as expected for their position in the periodic table, as heavier homologs of lutetium through osmium. They are expected to have ionic radii between those of their 5d transition metal homologs and their actinide pseudohomologs: for example, Rf4+ is calculated to have ionic radius 76 pm, between the values for Hf4+ (71 pm) and Th4+ (94 pm). Their ions should also be less polarizable than those of their 5d homologs. Relativistic effects are expected to reach a maximum at the end of this series, at roentgenium (element 111) and copernicium (element 112). Nevertheless, many important properties of the transactinides are still not yet known experimentally, though theoretical calculations have been performed.[15]

Elements 113 to 118, nihonium to oganesson, should form a 7p series, completing the seventh period in the periodic table. Their chemistry will be greatly influenced by the very strong relativistic stabilization of the 7s electrons and a strong spin–orbit coupling effect "tearing" the 7p subshell apart into two sections, one more stabilized (7p1/2, holding two electrons) and one more destabilized (7p3/2, holding four electrons). Lower oxidation states should be stabilized here, continuing group trends, as both the 7s and 7p1/2 electrons exhibit the inert-pair effect. These elements are expected to largely continue to follow group trends, though with relativistic effects playing an increasingly larger role. In particular, the large 7p splitting results in an effective shell closure at flerovium (element 114) and a hence much higher than expected chemical activity for oganesson (element 118).[15]

Element 118 is the last element that has been synthesized. The next two elements, 119 and 120, should form an 8s series and be an alkali and alkaline earth metal respectively. The 8s electrons are expected to be relativistically stabilized, so that the trend toward higher reactivity down these groups will reverse and the elements will behave more like their period 5 homologs, rubidium and strontium. The 7p3/2 orbital is still relativistically destabilized, potentially giving these elements larger ionic radii and perhaps even being able to participate chemically. In this region, the 8p electrons are also relativistically stabilized, resulting in a ground-state 8s28p1 valence electron configuration for element 121. Large changes are expected to occur in the subshell structure in going from element 120 to element 121: for example, the radius of the 5g orbitals should drop drastically, from 25 Bohr units in element 120 in the excited [Og] 5g1 8s1 configuration to 0.8 Bohr units in element 121 in the excited [Og] 5g1 7d1 8s1 configuration, in a phenomenon called "radial collapse". Element 122 should add either a further 7d or a further 8p electron to element 121's electron configuration. Elements 121 and 122 should be similar to actinium and thorium respectively.[15]

At element 121, the superactinide series is expected to begin, when the 8s electrons and the filling 8p1/2, 7d3/2, 6f5/2, and 5g7/2 subshells determine the chemistry of these elements. Complete and accurate calculations are not available for elements beyond 123 because of the extreme complexity of the situation:[63] the 5g, 6f, and 7d orbitals should have about the same energy level, and in the region of element 160 the 9s, 8p3/2, and 9p1/2 orbitals should also be about equal in energy. This will cause the electron shells to mix so that the block concept no longer applies very well, and will also result in novel chemical properties that will make positioning these elements in a periodic table very difficult.[15]

Beyond superheavy elements

It has been suggested that elements beyond Z = 126 be called beyond superheavy elements.[64] Other sources refer to elements around Z = 164 as hyperheavy elements.[65]

See also

Notes

  1. ^ In nuclear physics, an element is called heavy if its atomic number is high; lead (element 82) is one example of such a heavy element. The term "superheavy elements" typically refers to elements with atomic number greater than 103 (although there are other definitions, such as atomic number greater than 100[17] or 112;[18] sometimes, the term is presented an equivalent to the term "transactinide", which puts an upper limit before the beginning of the hypothetical superactinide series).[19] Terms "heavy isotopes" (of a given element) and "heavy nuclei" mean what could be understood in the common language—isotopes of high mass (for the given element) and nuclei of high mass, respectively.
  2. ^ In 2009, a team at the JINR led by Oganessian published results of their attempt to create hassium in a symmetric 136Xe + 136Xe reaction. They failed to observe a single atom in such a reaction, putting the upper limit on the cross section, the measure of probability of a nuclear reaction, as 2.5 pb.[20] In comparison, the reaction that resulted in hassium discovery, 208Pb + 58Fe, had a cross section of ~20 pb (more specifically, 19+19
    -11     pb), as estimated by the discoverers.[21]
  3. ^ The amount of energy applied to the beam particle to accelerate it can also influence the value of cross section. For example, in the 28
    14    Si
     + 1
    0    n
     → 28
    13    Al
     + 1
    1    p
     reaction, cross section changes smoothly from 370 mb at 12.3 MeV to 160 mb at 18.3 MeV, with a broad peak at 13.5 MeV with the maximum value of 380 mb.[25]
  4. ^ This figure also marks the generally accepted upper limit for lifetime of a compound nucleus.[30]
  5. ^ This separation is based on that the resulting nuclei move past the target more slowly then the unreacted beam nuclei. The separator contains electric and magnetic fields whose effects on a moving particle cancel out for a specific velocity of a particle.[32] Such separation can also be aided by a time-of-flight measurement and a recoil energy measurement; a combination of the two may allow to estimate the mass of a nucleus.[33]
  6. ^ Not all decay modes are caused by electrostatic repulsion. For example, beta decay is caused by the weak interaction.[40]
  7. ^ It was already known by the 1960s that ground states of nuclei differed in energy and shape as well as that certain magic numbers of nucleons corresponded to greater stability of a nucleus. However, it was assumed that there was no nuclear structure in superheavy nuclei as they were too deformed to form one.[45]
  8. ^ Since mass of a nucleus is not measured directly but is rather calculated from that of another nucleus, such measurement is called indirect. Direct measurements are also possible, but for the most part they have remained unavailable for superheavy nuclei.[50] The first direct measurement of mass of a superheavy nucleus was reported in 2018 at LBNL.[51] Mass was determined from the location of a nucleus after the transfer (the location helps determine its trajectory, which is linked to the mass-to-charge ratio of the nucleus, since the transfer was done in presence of a magnet).[52]
  9. ^ If the decay occurred in a vacuum, then since total momentum of an isolated system before and after the decay must be preserved, the daughter nucleus would also receive a small velocity. The ratio of the two velocities, and accordingly the ratio of the kinetic energies, would thus be inverse to the ratio of the two masses. The decay energy equals the sum of the known kinetic energy of the alpha particle and that of the daughter nucleus (an exact fraction of the former).[41] The calculations hold for an experiment as well, but the difference is that the nucleus does not move after the decay because it is tied to the detector.
  10. ^ Spontaneous fission was discovered by Soviet physicist Georgy Flerov,[53] a leading scientist at JINR, and thus it was a "hobbyhorse" for the facility.[54] In contrast, the LBL scientists believed fission information was not sufficient for a claim of synthesis of an element. They believed spontaneous fission had not been studied enough to use it for identification of a new element, since there was a difficulty of establishing that a compound nucleus had only ejected neutrons and not charged particles like protons or alpha particles.[30] They thus preferred to link new isotopes to the already known ones by successive alpha decays.[53]
  11. ^ For instance, element 102 was mistakenly identified in 1957 at the Nobel Institute of Physics in Stockholm, Stockholm County, Sweden.[55] There were no earlier definitive claims of creation of this element, and the element was assigned a name by its Swedish, American, and British discoverers, nobelium. It was later shown that the identification was incorrect.[56] The following year, RL was unable to reproduce the Swedish results and announced instead their synthesis of the element; that claim was also disproved later.[56] JINR insisted that they were the first to create the element and suggested a name of their own for the new element, joliotium;[57] the Soviet name was also not accepted (JINR later referred to the naming of the element 102 as "hasty").[58] This name was proposed to IUPAC in a written response to their ruling on priority of discovery claims of elements, signed 29 September 1992.[58] The name "nobelium" remained unchanged on account of its widespread usage.[59]

References

  1. ^ a b c d Hoffman, Darleane C.; Lee, Diana M.; Pershina, Valeria (2006). "Transactinides and the future elements". In Morss; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands: Springer Science+Business Media. ISBN 978-1-4020-3555-5.
  2. ^ Soverna S 2004, 'Indication for a gaseous element 112,' in U Grundinger (ed.), GSI Scientific Report 2003, GSI Report 2004-1, p. 187, ISSN 0174-0814
  3. ^ a b c d e f Mewes, J.-M.; Smits, O. R.; Kresse, G.; Schwerdtfeger, P. (2019). "Copernicium is a Relativistic Noble Liquid". Angewandte Chemie International Edition. doi:10.1002/anie.201906966.
  4. ^ Fricke, Burkhard (1975). "Superheavy elements: a prediction of their chemical and physical properties". Recent Impact of Physics on Inorganic Chemistry. Structure and Bonding. 21: 89–144. doi:10.1007/BFb0116498. ISBN 978-3-540-07109-9. Retrieved October 4, 2013.
  5. ^ Chemical Data. Copernicium - Cn, Royal Chemical Society
  6. ^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  7. ^ Oganessian, Yu. Ts.; Utyonkov, V. K.; Ibadullayev, D.; et al. (2022). "Investigation of 48Ca-induced reactions with 242Pu and 238U targets at the JINR Superheavy Element Factory". Physical Review C. 106 (24612). Bibcode:2022PhRvC.106b4612O. doi:10.1103/PhysRevC.106.024612. S2CID 251759318.
  8. ^ Eichler, R.; et al. (2007). "Chemical Characterization of Element 112". Nature. 447 (7140): 72–75. Bibcode:2007Natur.447...72E. doi:10.1038/nature05761. PMID 17476264. S2CID 4347419.
  9. ^ "Superheavy Element Discovery | Glenn T. Seaborg Institute". seaborg.llnl.gov. Retrieved September 2, 2024.
  10. ^ a b Neve, Francesco (2022). "Chemistry of superheavy transition metals". Journal of Coordination Chemistry. 75 (17–18): 2287–2307. doi:10.1080/00958972.2022.2084394. S2CID 254097024.
  11. ^ a b Mingos, Michael (1998). Essential Trends in Inorganic Chemistry. Oxford University Press. p. 387. ISBN 978-0-19-850109-1.
  12. ^ "A New Era of Discovery: the 2023 Long Range Plan for Nuclear Science" (PDF). U.S. Department of Energy. October 2023. Archived from the original (PDF) on October 5, 2023. Retrieved October 20, 2023 – via OSTI. Superheavy elements (Z > 102) are teetering at the limits of mass and charge.
  13. ^ Kragh, Helge (2017). "The search for superheavy elements: Historical and philosophical perspectives". arXiv:1708.04064 [physics.hist-ph].
  14. ^ IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004) (online draft of an updated version of the "Red Book" IR 3-6) Archived October 27, 2006, at the Wayback Machine
  15. ^ a b c d e f Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean, eds. (2006). The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands: Springer. ISBN 978-1-4020-3555-5.
  16. ^ "Kernchemie". www.kernchemie.de.
  17. ^ Krämer, K. (2016). "Explainer: superheavy elements". Chemistry World. Retrieved March 15, 2020.
  18. ^ "Discovery of Elements 113 and 115". Lawrence Livermore National Laboratory. Archived from the original on September 11, 2015. Retrieved March 15, 2020.
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Bibliography

History

Discovery

Copernicium was first created on February 9, 1996, at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany, by Sigurd Hofmann, Victor Ninov et al.[1] This element was created by firing accelerated zinc-70 nuclei at a target made of lead-208 nuclei in a heavy ion accelerator. A single atom of copernicium was produced with a mass number of 277. (A second was originally reported, but was found to have been based on data fabricated by Ninov, and was thus retracted.)[1]

208
82Pb + 70
30Zn → 278
112Cn* → 277
112Cn + 1
0n

In May 2000, the GSI successfully repeated the experiment to synthesize a further atom of copernicium-277.[2] This reaction was repeated at RIKEN using the Search for a Super-Heavy Element Using a Gas-Filled Recoil Separator set-up in 2004 and 2013 to synthesize three further atoms and confirm the decay data reported by the GSI team.[3][4] This reaction had also previously been tried in 1971 at the Joint Institute for Nuclear Research in Dubna, Russia to aim for 276Cn (produced in the 2n channel), but without success.[5]

The IUPAC/IUPAP Joint Working Party (JWP) assessed the claim of copernicium's discovery by the GSI team in 2001[6] and 2003.[7] In both cases, they found that there was insufficient evidence to support their claim. This was primarily related to the contradicting decay data for the known nuclide rutherfordium-261. However, between 2001 and 2005, the GSI team studied the reaction 248Cm(26Mg,5n)269Hs, and were able to confirm the decay data for hassium-269 and rutherfordium-261. It was found that the existing data on rutherfordium-261 was for an isomer,[8] now designated rutherfordium-261m.

In May 2009, the JWP reported on the claims of discovery of element 112 again and officially recognized the GSI team as the discoverers of element 112.[9] This decision was based on the confirmation of the decay properties of daughter nuclei as well as the confirmatory experiments at RIKEN.[10]

Work had also been done at the Joint Institute for Nuclear Research in Dubna, Russia from 1998 to synthesise the heavier isotope 283Cn in the hot fusion reaction 238U(48Ca,3n)283Cn; most observed atoms of 283Cn decayed by spontaneous fission, although an alpha decay branch to 279Ds was detected. While initial experiments aimed to assign the produced nuclide with its observed long half-life of 3 minutes based on its chemical behaviour, this was found to be not mercury-like as would have been expected (copernicium being under mercury in the periodic table),[10] and indeed now it appears that the long-lived activity might not have been from 283Cn at all, but its electron capture daughter 283Rg instead, with a shorter 4-second half-life associated with 283Cn. (Another possibility is assignment to a metastable isomeric state, 283mCn.)[11] While later cross-bombardments in the 242Pu+48Ca and 245Cm+48Ca reactions succeeded in confirming the properties of 283Cn and its parents 287Fl and 291Lv, and played a major role in the acceptance of the discoveries of flerovium and livermorium (elements 114 and 116) by the JWP in 2011, this work originated subsequent to the GSI's work on 277Cn and priority was assigned to the GSI.[10]

Naming

a painted portrait of Copernicus
Nicolaus Copernicus, who formulated a heliocentric model with the planets orbiting around the Sun, replacing Ptolemy's earlier geocentric model.

Using Mendeleev's nomenclature for unnamed and undiscovered elements, copernicium should be known as eka-mercury. In 1979, IUPAC published recommendations according to which the element was to be called ununbium (with the corresponding symbol of Uub),[12] a systematic element name as a placeholder, until the element was discovered (and the discovery then confirmed) and a permanent name was decided on. Although widely used in the chemical community on all levels, from chemistry classrooms to advanced textbooks, the recommendations were mostly ignored among scientists in the field, who either called it "element 112", with the symbol of E112, (112), or even simply 112.[13]

After acknowledging the GSI team's discovery, the IUPAC asked them to suggest a permanent name for element 112.[10][14] On 14 July 2009, they proposed copernicium with the element symbol Cp, after Nicolaus Copernicus "to honor an outstanding scientist, who changed our view of the world".[15]

During the standard six-month discussion period among the scientific community about the naming,[16][17] it was pointed out that the symbol Cp was previously associated with the name cassiopeium (cassiopium), now known as lutetium (Lu), and the compound cyclopentadiene.[18][19] For this reason, the IUPAC disallowed the use of Cp as a future symbol, prompting the GSI team to put forward the symbol Cn as an alternative. On 19 February 2010, the 537th anniversary of Copernicus' birth, IUPAC officially accepted the proposed name and symbol.[16][20]

Isotopes

Main article: Isotopes of copernicium
List of copernicium isotopes
Isotope Half-life[a] Decay
mode 		Discovery
year 		Discovery
reaction
Value ref
277Cn 0.85 ms [21] α 1996 208Pb(70Zn,n)
281Cn 0.18 s [22] α 2010 285Fl(—,α)
282Cn 0.91 ms [23] SF 2003 290Lv(—,2α)
283Cn 4.2 s [23] α, SF, EC? 2003 287Fl(—,α)
284Cn 98 ms [23] α, SF 2004 288Fl(—,α)
285Cn 28 s [23] α 1999 289Fl(—,α)
285mCn[b] 15 s [21] α 2012 293mLv(—,2α)
286Cn[b] 8.45 s [24] SF 2016 294Lv(—,2α)

Copernicium has no stable or naturally occurring isotopes. Several radioactive isotopes have been synthesized in the laboratory, either by fusing two atoms or by observing the decay of heavier elements. Seven different isotopes have been reported with mass numbers 277 and 281–286, and one unconfirmed metastable isomer in 285Cn has been reported.[25] Most of these decay predominantly through alpha decay, but some undergo spontaneous fission, and copernicium-283 may have an electron capture branch.[26]

The isotope copernicium-283 was instrumental in the confirmation of the discoveries of the elements flerovium and livermorium.[27]

Half-lives

All confirmed copernicium isotopes are extremely unstable and radioactive; in general, heavier isotopes are more stable than the lighter. The most stable known isotope, 285Cn, has a half-life of 29 seconds; 283Cn has a half-life of 4 seconds, and the unconfirmed 285mCn and 286Cn have half-lives of about 15 and 8.45 seconds respectively. Other isotopes have half-lives shorter than one second. 281Cn and 284Cn both have half-lives on the order of 0.1 seconds, and the other two isotopes have half-lives slightly under one millisecond.[26] It is predicted that the heavy isotopes 291Cn and 293Cn may have half-lives longer than a few decades, for they are predicted to lie near the center of the theoretical island of stability, and may have been produced in the r-process and be detectable in cosmic rays, though they would be about 10−12 times as abundant as lead.[28]

The lightest isotopes of copernicium have been synthesized by direct fusion between two lighter nuclei and as decay products (except for 277Cn, which is not known to be a decay product), while the heavier isotopes are only known to be produced by decay of heavier nuclei. The heaviest isotope produced by direct fusion is 283Cn; the three heavier isotopes, 284Cn, 285Cn, and 286Cn, have only been observed as decay products of elements with larger atomic numbers.[26]

In 1999, American scientists at the University of California, Berkeley, announced that they had succeeded in synthesizing three atoms of 293Og.[29] These parent nuclei were reported to have successively emitted three alpha particles to form copernicium-281 nuclei, which were claimed to have undergone alpha decay, emitting alpha particles with decay energy 10.68 MeV and half-life 0.90 ms, but their claim was retracted in 2001[30] as it had been based on data fabricated by Ninov.[31] This isotope was truly produced in 2010 by the same team; the new data contradicted the previous fabricated data.[32]

Predicted properties

Very few properties of copernicium or its compounds have been measured; this is due to its extremely limited and expensive production[33] and the fact that copernicium (and its parents) decays very quickly. A few singular chemical properties have been measured, as well as the boiling point, but properties of the copernicium metal remain generally unknown and for the most part, only predictions are available.

Chemical

Copernicium is the tenth and last member of the 6d series and is the heaviest group 12 element in the periodic table, below zinc, cadmium and mercury. It is predicted to differ significantly from the lighter group 12 elements. The valence s-subshells of the group 12 elements and period 7 elements are expected to be relativistically contracted most strongly at copernicium. This and the closed-shell configuration of copernicium result in it probably being a very noble metal. A standard reduction potential of +2.1 V is predicted for the Cn2+/Cn couple. Copernicium's predicted first ionization energy of 1155 kJ/mol almost matches that of the noble gas xenon at 1170.4 kJ/mol.[13] Copernicium's metallic bonds should also be very weak, possibly making it extremely volatile like the noble gases, and potentially making it gaseous at room temperature.[13][34] However, it should be able to form metal–metal bonds with copper, palladium, platinum, silver, and gold; these bonds are predicted to be only about 15–20 kJ/mol weaker than the analogous bonds with mercury.[13] In opposition to the earlier suggestion,[35] ab initio calculations at the high level of accuracy[36] predicted that the chemistry of singly-valent copernicium resembles that of mercury rather than that of the noble gases. The latter result can be explained by the huge spin-orbit interaction which significantly lowers the energy of the vacant 7p1/2 state of copernicium.

Once copernicium is ionized, its chemistry may present several differences from those of zinc, cadmium, and mercury. Due to the stabilization of 7s electronic orbitals and destabilization of 6d ones caused by relativistic effects, Cn2+ is likely to have a [Rn]5f146d87s2 electronic configuration, using the 6d orbitals before the 7s one, unlike its homologues. The fact that the 6d electrons participate more readily in chemical bonding means that once copernicium is ionized, it may behave more like a transition metal than its lighter homologues, especially in the possible +4 oxidation state. In aqueous solutions, copernicium may form the +2 and perhaps +4 oxidation states.[13] The diatomic ion Hg2+
2, featuring mercury in the +1 oxidation state, is well-known, but the Cn2+
2 ion is predicted to be unstable or even non-existent.[13] Copernicium(II) fluoride, CnF2, should be more unstable than the analogous mercury compound, mercury(II) fluoride (HgF2), and may even decompose spontaneously into its constituent elements. As the most electronegative reactive element, fluorine may be the only element able to oxidise copernicium even further to the +4 and even +6 oxidation states in CnF4 and CnF6; the latter may require matrix-isolation conditions to be detected, as in the disputed detection of HgF4. CnF4 should be more stable than CnF2.[37] In polar solvents, copernicium is predicted to preferentially form the CnF−
5 and CnF−
3 anions rather than the analogous neutral fluorides (CnF4 and CnF2, respectively), although the analogous bromide or iodide ions may be more stable towards hydrolysis in aqueous solution. The anions CnCl2−
4 and CnBr2−
4 should also be able to exist in aqueous solution.[13] The formation of thermodynamically stable copernicium(II) and (IV) fluorides would be analogous to the chemistry of xenon.[38] Analogous to mercury(II) cyanide (Hg(CN)2), copernicium is expected to form a stable cyanide, Cn(CN)2.[39]

Physical and atomic

Copernicium should be a dense metal, with a density of 14.0 g/cm3 in the liquid state at 300 K; this is similar to the known density of mercury, which is 13.534 g/cm3. (Solid copernicium at the same temperature should have a higher density of 14.7 g/cm3.) This results from the effects of copernicium's higher atomic weight being cancelled out by its larger interatomic distances compared to mercury.[38] Some calculations predicted copernicium to be a gas at room temperature due to its closed-shell electron configuration,[40] which would make it the first gaseous metal in the periodic table.[13][34] A 2019 calculation agrees with these predictions on the role of relativistic effects, suggesting that copernicium will be a volatile liquid bound by dispersion forces under standard conditions. Its melting point is estimated at 283±11 K and its boiling point at 340±10 K, the latter in agreement with the experimentally estimated value of 357+112
−108 K.[38] The atomic radius of copernicium is expected to be around 147 pm. Due to the relativistic stabilization of the 7s orbital and destabilization of the 6d orbital, the Cn+ and Cn2+ ions are predicted to give up 6d electrons instead of 7s electrons, which is the opposite of the behavior of its lighter homologues.[13]

In addition to the relativistic contraction and binding of the 7s subshell, the 6d5/2 orbital is expected to be destabilized due to spin-orbit coupling, making it behave similarly to the 7s orbital in terms of size, shape, and energy. Predictions of the expected band structure of copernicium are varied. Calculations in 2007 expected that copernicium may be a semiconductor[41] with a band gap of around 0.2 eV,[42] crystallizing in the hexagonal close-packed crystal structure.[42] However, calculations in 2017 and 2018 suggested that copernicium should be a noble metal at standard conditions with a body-centered cubic crystal structure: it should hence have no band gap, like mercury, although the density of states at the Fermi level is expected to be lower for copernicium than for mercury.[43][44] 2019 calculations then suggested that in fact copernicium has a large band gap of 6.4 ± 0.2 eV, which should be similar to that of the noble gas radon (predicted as 7.1 eV) and would make it an insulator; bulk copernicium is predicted by these calculations to be bound mostly by dispersion forces, like the noble gases.[38] Like mercury, radon, and flerovium, but not oganesson (eka-radon), copernicium is calculated to have no electron affinity.[45]

Experimental atomic gas phase chemistry

Interest in copernicium's chemistry was sparked by predictions that it would have the largest relativistic effects in the whole of period 7 and group 12, and indeed among all 118 known elements.[13] Copernicium is expected to have the ground state electron configuration [Rn] 5f14 6d10 7s2 and thus should belong to group 12 of the periodic table, according to the Aufbau principle. As such, it should behave as the heavier homologue of mercury and form strong binary compounds with noble metals like gold. Experiments probing the reactivity of copernicium have focused on the adsorption of atoms of element 112 onto a gold surface held at varying temperatures, in order to calculate an adsorption enthalpy. Owing to relativistic stabilization of the 7s electrons, copernicium shows radon-like properties. Experiments were performed with the simultaneous formation of mercury and radon radioisotopes, allowing a comparison of adsorption characteristics.[46]

The first chemical experiments on copernicium were conducted using the 238U(48Ca,3n)283Cn reaction. Detection was by spontaneous fission of the claimed parent isotope with half-life of 5 minutes. Analysis of the data indicated that copernicium was more volatile than mercury and had noble gas properties. However, the confusion regarding the synthesis of copernicium-283 has cast some doubt on these experimental results.[46] Given this uncertainty, between April–May 2006 at the JINR, a FLNR–PSI team conducted experiments probing the synthesis of this isotope as a daughter in the nuclear reaction 242Pu(48Ca,3n)287Fl.[46] (The 242Pu + 48Ca fusion reaction has a slightly larger cross-section than the 238U + 48Ca reaction, so that the best way to produce copernicium for chemical experimentation is as an overshoot product as the daughter of flerovium.)[47] In this experiment, two atoms of copernicium-283 were unambiguously identified and the adsorption properties were interpret to show that copernicium is a more volatile homologue of mercury, due to formation of a weak metal-metal bond with gold.[46] This agrees with general indications from some relativistic calculations that copernicium is "more or less" homologous to mercury.[48] However, it was pointed out in 2019 that this result may simply be due to strong dispersion interactions.[38]

In April 2007, this experiment was repeated and a further three atoms of copernicium-283 were positively identified. The adsorption property was confirmed and indicated that copernicium has adsorption properties in agreement with being the heaviest member of group 12.[46] These experiments also allowed the first experimental estimation of copernicium's boiling point: 84+112
−108 °C, so that it may be a gas at standard conditions.[41]

Because the lighter group 12 elements often occur as chalcogenide ores, experiments were conducted in 2015 to deposit copernicium atoms on a selenium surface to form copernicium selenide, CnSe. Reaction of copernicium atoms with trigonal selenium to form a selenide was observed, with -ΔHadsCn(t-Se) > 48 kJ/mol, with the kinetic hindrance towards selenide formation being lower for copernicium than for mercury. This was unexpected as the stability of the group 12 selenides tends to decrease down the group from ZnSe to HgSe.[49]

See also

Notes

  1. ^ Different sources give different values for half-lives; the most recently published values are listed.
  2. ^ a b This isotope is unconfirmed

References

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  2. ^ Hofmann, S.; et al. (2000). "New Results on Element 111 and 112" (PDF). European Physical Journal A. 14 (2). Gesellschaft für Schwerionenforschung: 147–157. Bibcode:2002EPJA...14..147H. doi:10.1140/epja/i2001-10119-x. S2CID 8773326. Archived from the original (PDF) on February 27, 2008. Retrieved March 2, 2008.
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  4. ^ Sumita, Takayuki; Morimoto, Kouji; Kaji, Daiya; Haba, Hiromitsu; Ozeki, Kazutaka; Sakai, Ryutaro; Yoneda, Akira; Yoshida, Atsushi; Hasebe, Hiroo; Katori, Kenji; Sato, Nozomi; Wakabayashi, Yasuo; Mitsuoka, Shin-Ichi; Goto, Shin-Ichi; Murakami, Masashi; Kariya, Yoshiki; Tokanai, Fuyuki; Mayama, Keita; Takeyama, Mirei; Moriya, Toru; Ideguchi, Eiji; Yamaguchi, Takayuki; Kikunaga, Hidetoshi; Chiba, Junsei; Morita, Kosuke (2013). "New Result on the Production of277Cn by the208Pb +70Zn Reaction". Journal of the Physical Society of Japan. 82 (2): 024202. Bibcode:2013JPSJ...82b4202S. doi:10.7566/JPSJ.82.024202.
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Bibliography

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