roentgenium ← copernicium → ununtrium Hg
Appearance unknown General properties Name, symbol, number copernicium, Cn, 112 Pronunciation //
Element category transition metal Group, period, block 12, 7, d Standard atomic weight  Electron configuration [Rn] 5f14 6d10 7s2
Electrons per shell 2, 8, 18, 32, 32, 18, 2
Physical properties Phase Unknown Atomic properties Oxidation states 4, 2
(a guess based on that of mercury)
Miscellanea CAS registry number 54084-26-3 Most stable isotopes Main article: Isotopes of copernicium iso NA half-life DM DE (MeV) DP 285aCn syn 29 s α 9.15,9.03? 281aDs 285bCn ? syn 8.9 m α 8.63 281bDs ? 284Cn syn 97 ms SF 283aCn syn 4 s 90% α 9.53,9.32,8.94 279Ds 10% SF 283bCn ?? syn ~ 7.0 m SF 282Cn syn 0.8 ms SF 281Cn syn 97 ms α 10.31 277Ds 277Cn syn 0.7 ms α 11.45,11.32 273Ds
Copernicium ( // koh-pər-nis-ee-əm) is a chemical element with symbol Cn and atomic number 112. It is an extremely radioactive synthetic element that on Earth can only be created in a laboratory. The most stable known isotope, copernicium-285, has a half-life of approximately 29 seconds, but it is possible that this copernicium isotope may have an isomer with a longer half-life, 8.9 min. It was first created in 1996 by the Gesellschaft für Schwerionenforschung (GSI; Centre for Heavy Ion Research). It is named after the astronomer Nicolaus Copernicus.
In the periodic table of the elements, it is a d-block element, which belongs to transactinide elements. During reactions with gold, it is shown to be a volatile metal and a group 12 element. Copernicium is calculated to have several properties that differ between it and its lighter homologues, zinc, cadmium and mercury; the most notable of them is withdrawing two 6d-electrons before 7s ones due to relativistic effects, which confirm copernicium as an undisputed transition metal. Copernicium is also calculated to show predominance of oxidation state +4, while mercury shows it in only one compound at extreme conditions and zinc and cadmium do not show it at all. Difficulty of oxidation of copernicium from its neutral state compared to group 12 elements has also been predicted.
In total, approximately 75 atoms of copernicium have been detected using various nuclear reactions.
- 1 History
- 2 Nucleosynthesis
- 3 Isotopes
- 4 Chemical properties
- 5 See also
- 6 References
- 7 External links
Copernicium was first created on February 9, 1996, at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany, by Sigurd Hofmann, Victor Ninov et al. 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 (the second was subsequently dismissed) of copernicium was produced with a mass number of 277.
82Pb + 70
30Zn → 278
112Cn → 277
112Cn + 1
In May 2000, the GSI successfully repeated the experiment to synthesize a further atom of copernicium-277. This reaction was repeated at RIKEN using the Search for a Super-Heavy Element Using a Gas-Filled Recoil Separator set-up in 2004 to synthesize two further atoms and confirm the decay data reported by the GSI team.
The IUPAC/IUPAP Joint Working Party (JWP) assessed the claim of discovery by the GSI team in 2001 and 2003. 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, now designated rutherfordium-261a.
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. This decision was based on the confirmation of the decay properties of daughter nuclei as well as the confirmatory experiments at RIKEN.
After acknowledging their discovery, the IUPAC asked the discovery team at GSI to suggest a permanent name for ununbium. 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." IUPAC delayed the official recognition of the name, pending the results of a six-month discussion period among the scientific community.
However, it was pointed out that the symbol Cp was previously associated with the name cassiopeium (cassiopium), now known as lutetium (Lu). Furthermore, the symbol Cp is also used in organometallic chemistry to denote the cyclopentadienyl ligand. 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. The name was also approved by the General Assembly of the International Union of Pure and Applied Physics (IUPAP) on November 4, 2011.
Super-heavy elements such as copernicium are produced by bombarding lighter elements in particle accelerators that induces fusion reactions. Whereas most of the isotopes of rutherfordium can be synthesized directly this way, some heavier ones have only been observed as decay products of elements with higher atomic numbers.
Depending on the energies involved, the former are separated into "hot" and "cold". In hot fusion reactions, very light, high-energy projectiles are accelerated toward very heavy targets such as actinides, giving rise to compound nuclei at high excitation energy (~40–50 MeV) that may either fission or evaporate several (3 to 5) neutrons. In cold fusion reactions, the produced fused nuclei have a relatively low excitation energy (~10–20 MeV), which decreases the probability that these products will undergo fission reactions. As the fused nuclei cool to the ground state, they require emission of only one or two neutrons, and thus, allows for the generation of more neutron-rich products. The latter is a distinct concept from that of where nuclear fusion claimed to be achieved at room temperature conditions (see cold fusion).
The first cold fusion reaction to produce copernicium was performed by GSI in 1996, who reported the detection of two decay chains of copernicium-277.
In a review of the data in 2000, the first decay chain was retracted. In a repeat of the reaction in 2000 they were able to synthesize a further atom. They attempted to measure the 1n excitation function in 2002 but suffered from a failure of the zinc-70 beam. The unofficial discovery of copernicium-277 was confirmed in 2004 at RIKEN, where researchers detected a further two atoms of the isotope and were able to confirm the decay data for the entire chain.
After the successful synthesis of copernicium-277, the GSI team performed a reaction using a 68Zn projectile in 1997 in an effort to study the effect of isospin (neutron richness) on the chemical yield.
The experiment was initiated after the discovery of a yield enhancement during the synthesis of darmstadtium isotopes using nickel-62 and nickel-64 ions. No decay chains of copernicium-275 were detected leading to a cross section limit of 1.2 picobarns (pb). However, the revision of the yield for the zinc-70 reaction to 0.5 pb does not rule out a similar yield for this reaction.
In 1990, after some early indications for the formation of isotopes of copernicium in the irradiation of a tungsten target with multi-GeV protons, a collaboration between GSI and the University of Jerusalem studied the foregoing reaction.
They were able to detect some spontaneous fission (SF) activity and a 12.5 MeV alpha decay, both of which they tentatively assigned to the radiative capture product copernicium-272 or the 1n evaporation residue copernicium-271. Both the TWG and JWP have concluded that a lot more research is required to confirm these conclusions.
In 1998, the team at the Flerov Laboratory of Nuclear Research (FLNR) in Dubna, Russia began a research program using calcium-48 nuclei in "warm" fusion reactions leading to super-heavy elements. In March 1998, they claimed to have synthesized two atoms of the element in the following reaction.
The product, copernicium-283, had a claimed half-life of 5 minutes, decaying by spontaneous fission.
The long half-life of the product initiated first chemical experiments on the gas phase atomic chemistry of copernicium. In 2000, Yuri Yukashev in Dubna repeated the experiment but was unable to observe any spontaneous fission with half-life of 5 minutes. The experiment was repeated in 2001 and an accumulation of eight fragments resulting from spontaneous fission were found in the low-temperature section, indicating that copernicium had radon-like properties. However, there is now some serious doubt about the origin of these results. To confirm the synthesis, the reaction was successfully repeated by the same team in January 2003, confirming the decay mode and half-life. They were also able to calculate an estimate of the mass of the spontaneous fission activity to ~285, lending support to the assignment.
The team at Lawrence Berkeley National Laboratory (LBNL) in Berkeley, United States entered the debate and performed the reaction in 2002. They were unable to detect any spontaneous fission and calculated a cross section limit of 1.6 pb for the detection of a single event.
The reaction was repeated in 2003–2004 by the team at Dubna using a slightly different set-up, the Dubna Gas-Filled Recoil Separator (DGFRS). This time, copernicium-283 was found to decay by emission of a 9.53 MeV alpha-particle with a half-life of 4 seconds. copernicium-282 was also observed in the 4n channel (emitting 4 neutrons).
In 2003, the team at GSI entered the debate and performed a search for the five-minute SF activity in chemical experiments. Like the Dubna team, they were able to detect seven SF fragments in the low temperature section. However, these SF events were uncorrelated, suggesting they were not from actual direct SF of copernicium nuclei and raised doubts about the original indications for radon-like properties. After the announcement from Dubna of different decay properties for copernicium-283, the GSI team repeated the experiment in September 2004. They were unable to detect any SF events and calculated a cross section limit of ~1.6 pb for the detection of one event, not in contradiction with the reported 2.5 pb yield by Dubna.
In May 2005, the GSI performed a physical experiment and identified a single atom of 283Cn decaying by SF with a short half-time suggesting a previously unknown SF branch. However, initial work by Dubna had detected several direct SF events but had assumed that the parent alpha decay had been missed. These results indicated that this was not the case.
The new decay data on copernicium-283 were confirmed in 2006 by a joint PSI-FLNR experiment aimed at probing the chemical properties of copernicium. Two atoms of copernicium-283 were observed in the decay of the parent ununquadium-287 nuclei. The experiment indicated that contrary to previous experiments, copernicium behaves as a typical member of group 12, demonstrating properties of a volatile metal.
Finally, the team at GSI successfully repeated their physical experiment in January 2007, and detected three atoms of copernicium-283, confirming both the alpha and SF decay modes.
As such, the 5 minutes SF activity is still unconfirmed and unidentified. It is possible that it refers to an isomer, namely copernicium-283b, whose yield is dependent upon the exact production methods.
The team at FLNR studied this reaction in 2004. They were unable to detect any atoms of copernicium and calculated a cross section limit of 0.6 pb. The team concluded that this indicated that the neutron mass number for the compound nucleus had an effect on the yield of evaporation residues.
List of copernicium isotopes observed by decay Evaporation residue Observed copernicium isotope 285Uuq 281Cn 294Uuo, 290Uuh, 286Uuq 282Cn 291Uuh, 287Uuq 283Cn 292Uuh, 288Uuq 284Cn 293Uuh, 289Uuq 285Cn
Copernicium has been observed as decay products of ununquadium. Ununquadium currently has five known isotopes, all of which have been shown to undergo alpha decays to become a copernicium nuclei, with mass numbers between 281 and 285. Copernicium isotopes with mass numbers 281, 284 and 285 to date have only been produced by ununquadium nuclei decay. Parent ununquadium nuclei can be themselves decay products of ununhexium or ununoctium. To date, no other elements have been known to decay to copernicium.
For example, in May 2006, the Dubna team (JINR) identified copernicium-282 as a final product in the decay of ununoctium via the alpha decay sequence. It was found that the final nucleus undergoes spontaneous fission.
118Uuo → 290
116Uuh + 4
116Uuh → 286
114Uuq + 4
114Uuq → 282
112Cn + 4
In the claimed synthesis of ununoctium-293 in 1999, copernicium-281 was identified as decaying by emission of a 10.68 MeV alpha particle with half-life 0.90 ms. The claim was retracted in 2001. This isotope was finally created in 2010 and its decay properties supported that the previous data was wrong.
List of copernicium isotopes Isotope Half-life
Reaction 277Cn 0.69 ms α 1996 208Pb(70Zn,n) 281Cn 97 ms α 2010 285Uuq(—,α) 282Cn 0.8 ms SF 2004 238U(48Ca,4n) 283Cn 4 s α, SF 2002 238U(48Ca,3n) 283bCn ? 5 min ? α 1998 238U(48Ca,3n) 284Cn 97 ms SF 2002 288Uuq(—,α) 285Cn 29 s α 1999 289Uuq(—,α) 285bCn ? 8.9 min ? α 1999 289Uuq(—,α)
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. Six different isotopes have been reported with atomic masses from 281 to 285, and 277, two of which, copernicium-283 and copernicium-285, have known metastable states. Most of these decay predominantly through alpha decay, but some undergo spontaneous fission.
All copernicium isotopes are extremely unstable and radioactive; in general, heavier isotopes are more stable than the lighter. The most stable isotope, copernicium-285, has a half-life of 29 seconds, although it is suspected that this isotope has an isomer with a half-life of 8.9 minutes, and copernicium-283 may have an isomer with a half-life of about 5 minutes. Other isotopes have half-lives shorter than 0.1 seconds. Copernicium-281 and copernicium-284 have half-life of 97 ms, and the other two isotopes have half-lives slightly under one millisecond.
The lightest isotopes were synthesized by direct fusion between two lighter nuclei and as decay products (except for copernicium-277, which is 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 copernicium-283; the two heavier isotopes, copernicium-284 and copernicium-285 have only been observed as decay products of elements with larger atomic numbers. In 1999, American scientists at the University of California, Berkeley, announced that they had succeeded in synthesizing three atoms of 293118. These parent nuclei were reported to have successively emitted three alpha particles to form copernicium-281 nuclei, which were claimed to have undergone an alpha decay, emitting an alpha particle with decay energy of 10.68 MeV and half-life 0.90 ms, but their claim was retracted in 2001. The isotope, however, was produced in 2010 by the same team, confirming the previous data was wrong.
First experiments on the synthesis of 283Cn produced a SF activity with half-life ~5 min. This activity was also observed from the alpha decay of ununquadium-287. The decay mode and half-life were also confirmed in a repetition of the first experiment. Later, copernicium-283 was observed to undergo 9.52 MeV alpha decay and SF with a half-life of 3.9 s. It has also been found that alpha decay of copernicium-283 leads to different excited states of darmstadtium-279. These results suggest the assignment of the two activities to two different isomeric levels in copernicium-283, creating copernicium-283a and copernicium-283b.
Copernicium-285 has only been observed as a decay product of ununquadium-289 and ununhexium-293; during the first recorded synthesis of ununquadium, one ununquadium-289 was created, which alpha decayed to copernicium-285, which itself emitted an alpha particle in 29 seconds, releasing 9.15 or 9.03 MeV. However, the first successful experiment of ununhexium synthesis, when ununhexium-293 was created, it was shown that the created nuclide alpha decayed to ununquadium-289, decay data for which differed from the known values significantly. Although unconfirmed, it is highly possible that this is associated with an isomer. The resulted nuclide decayed to copernicium-285, which emitted an alpha article with a half-life of 8.9 minutes, releasing 8.63 MeV. Similar to its parent, it is believed to be a nuclear isomer, namely copernicium-285b.
Extrapolated oxidation states
Copernicium is the last member of the 6d series of transition metals and the heaviest group 12 element in the periodic table, below zinc, cadmium and mercury. It is predicted to differ significantly from lighter group 12 elements. Due to stabilization of 7s electronic orbitals and destabilization of 6d ones caused by relativistic effects, Cn2+ is likely to have [Rn]5f146d87s2 electronic configuration, breaking 6d orbitals before 7s one, unlike its homologues. In water solutions, copernicium is likely to form +2 and +4 oxidation states, with the latter one being more stable. Among lighter group 12 members, for which the +2 oxidation state is the most common, only mercury can show +4 oxidation state, but it is highly uncommon, existing at only one compound (mercury(IV) fluoride, HgF4) at extreme conditions. The analogous compound for copernicium, CnF4, is predicted to be more stable. The diatomic ion Hg2+
2, featuring mercury in +1 oxidation state is well-known, but the Cn2+
2 ion is predicted to be unstable or even non-existent. Oxidation of copernicium from its neutral state is also likely to be harder than those of previous group 12 members.
Experimental atomic gas phase chemistry
Copernicium has the ground state electron configuration [Rn]5f146d107s2 and thus should belong to group 12 of the periodic table, according to 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. Due 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.
The first experiments 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. 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)287Uuq. In this experiment, two atoms of copernicium-283 were unambiguously identified and the adsorption properties indicated that copernicium is a more volatile homologue of mercury, due to formation of a weak metal-metal bond with gold, placing it firmly in group 12.
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 completely in agreement with being the heaviest member of group 12.
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Periodic table H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Uuq Uup Uuh Uus Uuo Alkali metals Alkaline earth metals Lanthanides Actinides Transition metals Other metals Metalloids Other nonmetals Halogens Noble gases Unknown chem. properties Large version Always considered Speculated
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