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= Darmstadtium =
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Introduction
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Darmstadtium is a synthetic chemical element; it has symbol Ds and
atomic number 110. It is extremely radioactive: the most stable known
isotope, darmstadtium-281, has a half-life of approximately 14
seconds. Darmstadtium was first created in November 1994 by the GSI
Helmholtz Centre for Heavy Ion Research in the city of Darmstadt,
Germany, after which it was named.
In the periodic table, it is a d-block transactinide element. It is a
member of the 7th period and is placed in the group 10 elements,
although no chemical experiments have yet been carried out to confirm
that it behaves as the heavier homologue to platinum in group 10 as
the eighth member of the 6d series of transition metals. Darmstadtium
is calculated to have similar properties to its lighter homologues,
nickel, palladium, and platinum.
Discovery
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Darmstadtium was first discovered on November 9, 1994, at the
Institute for Heavy Ion Research (Gesellschaft für
Schwerionenforschung, GSI) in Darmstadt, Germany, by Peter Armbruster
and Gottfried Münzenberg, under the direction of Sigurd Hofmann. The
team bombarded a lead-208 target with accelerated nuclei of nickel-62
in a heavy ion accelerator and detected a single atom of the isotope
darmstadtium-269:
Two more atoms followed on November 12 and 17. (Yet another was
originally reported to have been found on November 11, but it turned
out to be based on data fabricated by Victor Ninov, and was later
retracted.)
In the same series of experiments, the same team also carried out the
reaction using heavier nickel-64 ions. During two runs, 9 atoms of
were convincingly detected by correlation with known daughter decay
properties:
Prior to this, there had been failed synthesis attempts in 1986-87 at
the Joint Institute for Nuclear Research in Dubna (then in the Soviet
Union) and in 1990 at the GSI. A 1995 attempt at the Lawrence Berkeley
National Laboratory resulted in signs suggesting but not pointing
conclusively at the discovery of a new isotope formed in the
bombardment of with , and a similarly inconclusive 1994 attempt at
the JINR showed signs of being produced from and . Each team
proposed its own name for element 110: the American team proposed
'hahnium' after Otto Hahn in an attempt to resolve the controversy of
naming element 105 (which they had long been suggesting this name
for), the Russian team proposed 'becquerelium' after Henri Becquerel,
and the German team proposed 'darmstadtium' after Darmstadt, the
location of their institute. The IUPAC/IUPAP Joint Working Party (JWP)
recognised the GSI team as discoverers in their 2001 report, giving
them the right to suggest a name for the element.
Naming
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Using Mendeleev's nomenclature for unnamed and undiscovered elements,
darmstadtium should be known as 'eka-platinum'. In 1979, IUPAC
published recommendations according to which the element was to be
called 'ununnilium' (with the corresponding symbol of 'Uun'), 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
called it "element 110", with the symbol of 'E110', '(110)' or even
simply '110'.
In 1996, the Russian team proposed the name 'becquerelium' after Henri
Becquerel. The American team in 1997 proposed the name 'hahnium' after
Otto Hahn (previously this name had been used for element 105).
The name 'darmstadtium' (Ds) was suggested by the GSI team in honor of
the city of Darmstadt, where the element was discovered. The GSI team
originally also considered naming the element 'wixhausium', after the
suburb of Darmstadt known as Wixhausen where the element was
discovered, but eventually decided on 'darmstadtium'. 'Policium' had
also been proposed as a joke due to the emergency telephone number in
Germany being 1-1-0. The new name 'darmstadtium' was officially
recommended by IUPAC on August 16, 2003.
Isotopes
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{{Isotopes summary
|element=darmstadtium
|reaction_ref=
|isotopes=
}}
Darmstadtium 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.
Eleven different isotopes of darmstadtium have been reported with
atomic masses 267, 269-271, 273, 275-277, and 279-281, although
darmstadtium-267 is unconfirmed. Three darmstadtium isotopes,
darmstadtium-270, darmstadtium-271, and darmstadtium-281, have known
metastable states, although that of darmstadtium-281 is unconfirmed.
Most of these decay predominantly through alpha decay, but some
undergo spontaneous fission.
Stability and half-lives
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All darmstadtium isotopes are extremely unstable and radioactive; in
general, the heavier isotopes are more stable than the lighter. The
most stable known darmstadtium isotope, 281Ds, is also the heaviest
known darmstadtium isotope; it has a half-life of 14 seconds. The
isotope 279Ds has a half-life of 0.18 seconds, while the unconfirmed
281mDs has a half-life of 0.9 seconds. The remaining isotopes and
metastable states have half-lives between 1 microsecond and 70
milliseconds. Some unknown darmstadtium isotopes may have longer
half-lives, however.
Theoretical calculation in a quantum tunneling model reproduces the
experimental alpha decay half-life data for the known darmstadtium
isotopes. It also predicts that the undiscovered isotope 294Ds, which
has a magic number of neutrons (184), would have an alpha decay
half-life on the order of 311 years; exactly the same approach
predicts a ~350-year alpha half-life for the non-magic 293Ds isotope,
however.
Predicted properties
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Other than nuclear properties, no properties of darmstadtium or its
compounds have been measured; this is due to its extremely limited and
expensive production and the fact that darmstadtium (and its parents)
decays very quickly. Properties of darmstadtium metal remain unknown
and only predictions are available.
Chemical
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Darmstadtium is the eighth member of the 6d series of transition
metals, and should be much like the platinum group metals.
Calculations on its ionization potentials and atomic and ionic radii
are similar to that of its lighter homologue platinum, thus implying
that darmstadtium's basic properties will resemble those of the other
group 10 elements, nickel, palladium, and platinum.
Prediction of the probable chemical properties of darmstadtium has not
received much attention recently. Darmstadtium should be a very noble
metal. The predicted standard reduction potential for the Ds2+/Ds
couple is 1.7 V. Based on the most stable oxidation states of the
lighter group 10 elements, the most stable oxidation states of
darmstadtium are predicted to be the +6, +4, and +2 states; however,
the neutral state is predicted to be the most stable in aqueous
solutions. In comparison, only platinum is known to show the maximum
oxidation state in the group, +6, while the most stable state is +2
for both nickel and palladium. It is further expected that the maximum
oxidation states of elements from bohrium (element 107) to
darmstadtium (element 110) may be stable in the gas phase but not in
aqueous solution. Darmstadtium hexafluoride (DsF6) is predicted to
have very similar properties to its lighter homologue platinum
hexafluoride (PtF6), having very similar electronic structures and
ionization potentials. It is also expected to have the same octahedral
molecular geometry as PtF6. Other predicted darmstadtium compounds are
darmstadtium carbide (DsC) and darmstadtium tetrachloride (DsCl4),
both of which are expected to behave like their lighter homologues.
Unlike platinum, which preferentially forms a cyanide complex in its
+2 oxidation state, Pt(CN)2, darmstadtium is expected to
preferentially remain in its neutral state and form instead, forming
a strong Ds-C bond with some multiple bond character.
Physical and atomic
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Darmstadtium is expected to be a solid under normal conditions and to
crystallize in the body-centered cubic structure, unlike its lighter
congeners which crystallize in the face-centered cubic structure,
because it is expected to have different electron charge densities
from them. It should be a very heavy metal with a density of around
26-27 g/cm3. In comparison, the densest known element that has had its
density measured, osmium, has a density of only 22.61 g/cm3.
The outer electron configuration of darmstadtium is calculated to be
6d8 7s2, which obeys the Aufbau principle and does not follow
platinum's outer electron configuration of 5d9 6s1. This is due to the
relativistic stabilization of the 7s2 electron pair over the whole
seventh period, so that none of the elements from 104 to 112 are
expected to have electron configurations violating the Aufbau
principle. The atomic radius of darmstadtium is expected to be around
132 pm.
Experimental chemistry
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Unambiguous determination of the chemical characteristics of
darmstadtium has yet to have been established due to the short
half-lives of darmstadtium isotopes and a limited number of likely
volatile compounds that could be studied on a very small scale. One of
the few darmstadtium compounds that are likely to be sufficiently
volatile is darmstadtium hexafluoride (), as its lighter homologue
platinum hexafluoride () is volatile above 60 °C and therefore the
analogous compound of darmstadtium might also be sufficiently
volatile; a volatile octafluoride () might also be possible. For
chemical studies to be carried out on a transactinide, at least four
atoms must be produced, the half-life of the isotope used must be at
least 1 second, and the rate of production must be at least one atom
per week. Even though the half-life of 281Ds, the most stable
confirmed darmstadtium isotope, is 14 seconds, long enough to perform
chemical studies, another obstacle is the need to increase the rate of
production of darmstadtium isotopes and allow experiments to carry on
for weeks or months so that statistically significant results can be
obtained. Separation and detection must be carried out continuously to
separate out the darmstadtium isotopes and have automated systems
experiment on the gas-phase and solution chemistry of darmstadtium, as
the yields for heavier elements are predicted to be smaller than those
for lighter elements; some of the separation techniques used for
bohrium and hassium could be reused. However, the experimental
chemistry of darmstadtium has not received as much attention as that
of the heavier elements from copernicium to livermorium.
The more neutron-rich darmstadtium isotopes are the most stable and
are thus more promising for chemical studies. However, they can only
be produced indirectly from the alpha decay of heavier elements, and
indirect synthesis methods are not as favourable for chemical studies
as direct synthesis methods. The more neutron-rich isotopes 276Ds and
277Ds might be produced directly in the reaction between thorium-232
and calcium-48, but the yield was expected to be low. Following
several unsuccessful attempts, 276Ds was produced in this reaction in
2022 and observed to have a half-life less than a millisecond and a
low yield, in agreement with predictions. Additionally, 277Ds was
successfully synthesized using indirect methods (as a granddaughter of
285Fl) and found to have a short half-life of 3.5 ms, not long enough
to perform chemical studies. The only known darmstadtium isotope with
a half-life long enough for chemical research is 281Ds, which would
have to be produced as the granddaughter of 289Fl.
See also
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* Island of stability
External links
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* [
http://www.periodicvideos.com/videos/110.htm Darmstadtium] at 'The
Periodic Table of Videos' (University of Nottingham)
License
=========
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Original Article:
http://en.wikipedia.org/wiki/Darmstadtium
