Copernicium is a chemical element with symbol Cn and atomic number 112. It is an extremely
radioactive synthetic element that 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 a nuclear isomer with a longer half-life, 8.9 min.
Copernicium was first created in 1996 by the GSI Helmholtz Centre for Heavy Ion Research
near Darmstadt, Germany. It is named after the astronomer Nicolaus Copernicus.
In the periodic table of the elements, it is a d-block transactinide element. During
reactions with gold, it has been shown to be an extremely volatile metal and a group
12 element, and it may even be a gas at standard temperature and pressure. 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 a predominance of the oxidation state +4, while mercury shows it in only one compound
at extreme conditions and zinc and cadmium do not show it at all. It has also been predicted
to be more difficult to oxidise copernicium from its neutral state than the other group
12 elements. In total, approximately 75 atoms of copernicium
have been detected using various nuclear reactions.
History Official discovery
Copernicium was first created on February 9, 1996, at the Gesellschaft für Schwerionenforschung
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 of copernicium was produced with a mass number of 277.
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. 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 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-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. This decision was based on
the confirmation of the decay properties of daughter nuclei as well as the confirmatory
experiments at RIKEN. Naming
After acknowledging their discovery, the IUPAC asked the discovery team at GSI to suggest
a permanent name for element 112. 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". During the standard six-month discussion period
among the scientific community about the naming, it was pointed out that the symbol Cp was
previously associated with the name cassiopeium, now known as lutetium. 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.
Isotopes
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. The isotope copernicium-283 was instrumental
in the confirmation of the discoveries of the elements flerovium and livermorium.
Half-lives 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. It is predicted that the heavy
isotopes copernicium-291 and copernicium-293 may have half-lives of around 1200 years,
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.
The lightest isotopes were synthesized by direct fusion between two lighter nuclei and
as decay products, 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. The new data contradicted the previous data.
Predicted properties Chemical
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 the 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 a [Rn]5f146d87s2
electronic configuration, using the 6d orbitals before the 7s one, unlike its homologues.
The fact that the 6d electrons participate readily in chemical bonding mean that copernicium
should behave more like a transition metal than its lighter homologues, especially in
the +4 oxidation state. In water solutions, copernicium is likely to form the +2 and +4
oxidation states, with the latter one being more stable. Among the lighter group 12 members,
for which the +2 oxidation state is the most common, only mercury can show the +4 oxidation
state, but it is highly uncommon, existing at only one compound fluoride, HgF4) at extreme
conditions. The analogous compound for copernicium, copernicium(IV) fluoride, 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 more
difficult than those of previous group 12 members. Copernicium(II) fluoride, CnF2, should
be more unstable than the analogous mercury compound, mercury(II) fluoride, and may even
decompose spontaneously into its constituent elements. In polar solvents, copernicium is
predicted to preferentially form the CnF− 5 and CnF−
3 anions rather than the analogous neutral fluorides, 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.
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. Its metallic bonds should also be very weak,
possibly making it extremely volatile, like the noble gases, and potentially making it
gaseous at room temperature. 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. Physical and atomic
Copernicium should be a very heavy metal with a density of around 23.7 g/cm3 in the solid
state; in comparison, the most dense known element that has had its density measured,
osmium, has a density of only 22.61 g/cm3. This results from copernicium's high atomic
weight, the lanthanide and actinide contractions, and relativistic effects, although production
of enough copernicium to measure this quantity would be impractical, and the sample would
quickly decay. However, some calculations predict copernicium to be a gas at room temperature,
the first gaseous metal in the periodic table, due to the closed-shell electron configurations
of copernicium and flerovium. 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.
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. Hence copernicium may not be a
noble transition metal, but rather a semiconductor with a band gap of around 0.2 eV. Copernicium
is expected to crystallize in the hexagonal close-packed crystal structure, with lattice
parameters a = 332 pm and c = 540 pm. The c/a ratio of 1.63 is the ideal value,
establishing a kinship between solid copernicium and the solid noble gases, though its cohesive
energy should be on the order of that of mercury rather than be near the lower value of the
noble gases. 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. Copernicium has the ground
state electron configuration [Rn]5f146d107s2 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.
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)287Fl. 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. These experiments also allowed the first experimental estimation of copernicium's
boiling point: 84+112 −108 °C.
See also Island of stability
References
External links Copernicium at The Periodic Table of Videos