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= Moscovium =
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Introduction
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Moscovium is a synthetic chemical element; it has symbol Mc and atomic
number 115. It was first synthesized in 2003 by a joint team of
Russian and American scientists at the Joint Institute for Nuclear
Research (JINR) in Dubna, Russia. In December 2015, it was recognized
as one of four new elements by the Joint Working Party of
international scientific bodies IUPAC and IUPAP. On 28 November 2016,
it was officially named after the Moscow Oblast, in which the JINR is
situated.
Moscovium is an extremely radioactive element: its most stable known
isotope, moscovium-290, has a half-life of only 0.65 seconds. In the
periodic table, it is a p-block transactinide element. It is a member
of the 7th period and is placed in group 15 as the heaviest pnictogen.
Moscovium is calculated to have some properties similar to its lighter
homologues, nitrogen, phosphorus, arsenic, antimony, and bismuth, and
to be a post-transition metal, although it should also show several
major differences from them. In particular, moscovium should also have
significant similarities to thallium, as both have one rather loosely
bound electron outside a quasi-closed shell. Chemical experimentation
on single atoms has confirmed theoretical expectations that moscovium
is less reactive than its lighter homologue bismuth. Over a hundred
atoms of moscovium have been observed to date, all of which have been
shown to have mass numbers from 286 to 290.
Discovery
===========
The first successful synthesis of moscovium was by a joint team of
Russian and American scientists in August 2003 at the Joint Institute
for Nuclear Research (JINR) in Dubna, Russia. Headed by Russian
nuclear physicist Yuri Oganessian, the team included American
scientists of the Lawrence Livermore National Laboratory. The
researchers on February 2, 2004, stated in 'Physical Review C' that
they bombarded americium-243 with calcium-48 ions to produce four
atoms of moscovium. These atoms decayed by emission of alpha-particles
to nihonium in about 100 milliseconds.
The Dubna-Livermore collaboration strengthened their claim to the
discoveries of moscovium and nihonium by conducting chemical
experiments on the final decay product 268Db. None of the nuclides in
this decay chain were previously known, so existing experimental data
was not available to support their claim. In June 2004 and December
2005, the presence of a dubnium isotope was confirmed by extracting
the final decay products, measuring spontaneous fission (SF)
activities and using chemical identification techniques to confirm
that they behave like a group 5 element (as dubnium is known to be in
group 5 of the periodic table). Both the half-life and the decay mode
were confirmed for the proposed 268Db, lending support to the
assignment of the parent nucleus to moscovium. However, in 2011, the
IUPAC/IUPAP Joint Working Party (JWP) did not recognize the two
elements as having been discovered, because current theory could not
distinguish the chemical properties of group 4 and group 5 elements
with sufficient confidence. Furthermore, the decay properties of all
the nuclei in the decay chain of moscovium had not been previously
characterized before the Dubna experiments, a situation which the JWP
generally considers "troublesome, but not necessarily exclusive".
Road to confirmation
======================
Two heavier isotopes of moscovium, 289Mc and 290Mc, were discovered in
2009-2010 as daughters of the tennessine isotopes 293Ts and 294Ts; the
isotope 289Mc was later also synthesized directly and confirmed to
have the same properties as found in the tennessine experiments.
In 2011, the Joint Working Party of international scientific bodies
International Union of Pure and Applied Chemistry (IUPAC) and
International Union of Pure and Applied Physics (IUPAP) evaluated the
2004 and 2007 Dubna experiments, and concluded that they did not meet
the criteria for discovery. Another evaluation of more recent
experiments took place within the next few years, and a claim to the
discovery of moscovium was again put forward by Dubna. In August 2013,
a team of researchers at Lund University and at the Gesellschaft für
Schwerionenforschung (GSI) in Darmstadt, Germany announced they had
repeated the 2004 experiment, confirming Dubna's findings.
Simultaneously, the 2004 experiment had been repeated at Dubna, now
additionally also creating the isotope 289Mc that could serve as a
cross-bombardment for confirming the discovery of the tennessine
isotope 293Ts in 2010. Further confirmation was published by the team
at the Lawrence Berkeley National Laboratory in 2015.
In December 2015, the IUPAC/IUPAP Joint Working Party recognized the
element's discovery and assigned the priority to the Dubna-Livermore
collaboration of 2009-2010, giving them the right to suggest a
permanent name for it. While they did not recognise the experiments
synthesising 287Mc and 288Mc as persuasive due to the lack of a
convincing identification of atomic number via cross-reactions, they
recognised the 293Ts experiments as persuasive because its daughter
289Mc had been produced independently and found to exhibit the same
properties.
In May 2016, Lund University (Lund, Scania, Sweden) and GSI cast some
doubt on the syntheses of moscovium and tennessine. The decay chains
assigned to 289Mc, the isotope instrumental in the confirmation of the
syntheses of moscovium and tennessine, were found based on a new
statistical method to be too different to belong to the same nuclide
with a reasonably high probability. The reported 293Ts decay chains
approved as such by the JWP were found to require splitting into
individual data sets assigned to different tennessine isotopes. It was
also found that the claimed link between the decay chains reported as
from 293Ts and 289Mc probably did not exist. (On the other hand, the
chains from the non-approved isotope 294Ts were found to be
congruent.) The multiplicity of states found when nuclides that are
not even-even undergo alpha decay is not unexpected and contributes to
the lack of clarity in the cross-reactions. This study criticized the
JWP report for overlooking subtleties associated with this issue, and
considered it "problematic" that the only argument for the acceptance
of the discoveries of moscovium and tennessine was a link they
considered to be doubtful.
On June 8, 2017, two members of the Dubna team published a journal
article answering these criticisms, analysing their data on the
nuclides 293Ts and 289Mc with widely accepted statistical methods,
noted that the 2016 studies indicating non-congruence produced
problematic results when applied to radioactive decay: they excluded
from the 90% confidence interval both average and extreme decay times,
and the decay chains that would be excluded from the 90% confidence
interval they chose were more probable to be observed than those that
would be included. The 2017 reanalysis concluded that the observed
decay chains of 293Ts and 289Mc were consistent with the assumption
that only one nuclide was present at each step of the chain, although
it would be desirable to be able to directly measure the mass number
of the originating nucleus of each chain as well as the excitation
function of the 243Am+48Ca reaction.
Naming
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Using Mendeleev's nomenclature for unnamed and undiscovered elements,
moscovium is sometimes known as 'eka-bismuth'. In 1979, IUPAC
recommended that the placeholder systematic element name 'ununpentium'
(with the corresponding symbol of 'Uup') be used until the discovery
of the element is confirmed and a permanent name is decided. 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 115",
with the symbol of 'E115', '(115)' or even simply '115'.
On 30 December 2015, discovery of the element was recognized by the
International Union of Pure and Applied Chemistry (IUPAC). According
to IUPAC recommendations, the discoverer(s) of a new element has the
right to suggest a name.
A suggested name was 'langevinium', after Paul Langevin. Later, the
Dubna team mentioned the name 'moscovium' several times as one among
many possibilities, referring to the Moscow Oblast where Dubna is
located.
In June 2016, IUPAC endorsed the latter proposal to be formally
accepted by the end of the year, which it was on 28 November 2016. The
naming ceremony for moscovium, tennessine, and oganesson was held on 2
March 2017 at the Russian Academy of Sciences in Moscow.
Other routes of synthesis
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In 2024, the team at JINR reported the observation of one decay chain
of 289Mc while studying the reaction between 242Pu and 50Ti, aimed at
producing more neutron-deficient livermorium isotopes in preparation
for synthesis attempts of elements 119 and 120. This was the first
successful report of a charged-particle exit channel - the evaporation
of a proton and two neutrons, rather than only neutrons, as the
compound nucleus de-excites to the ground state - in a hot fusion
reaction between an actinide target and a projectile with atomic
number greater than or equal to 20. Such reactions have been proposed
as a novel synthesis route for yet-undiscovered isotopes of superheavy
elements with several neutrons more than the known ones, which may be
closer to the theorized island of stability and have longer
half-lives. In particular, the isotopes 291Mc-293Mc may be reachable
in these types of reactions within current detection limits.
Predicted properties
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Other than nuclear properties, no properties of moscovium or its
compounds have been measured; this is due to its extremely limited and
expensive production and the fact that it decays very quickly.
Properties of moscovium remain unknown and only predictions are
available.
Nuclear stability and isotopes
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Moscovium is expected to be within an island of stability centered on
copernicium (element 112) and flerovium (element 114). Due to the
expected high fission barriers, any nucleus within this island of
stability exclusively decays by alpha decay and perhaps some electron
capture and beta decay. Although the known isotopes of moscovium do
not actually have enough neutrons to be on the island of stability,
they can be seen to approach the island as in general, the heavier
isotopes are the longer-lived ones.
The hypothetical isotope 291Mc is an especially interesting case as it
has only one neutron more than the heaviest known moscovium isotope,
290Mc. It could plausibly be synthesized as the daughter of 295Ts,
which in turn could be made from the reaction . Calculations show that
it may have a significant electron capture or positron emission decay
mode in addition to alpha decay and also have a relatively long
half-life of several seconds. This would produce 291Fl, 291Nh, and
finally 291Cn which is expected to be in the middle of the island of
stability and have a half-life of about 1200 years, affording the most
likely hope of reaching the middle of the island using current
technology. Possible drawbacks are that the cross section of the
production reaction of 295Ts is expected to be low and the decay
properties of superheavy nuclei this close to the line of beta
stability are largely unexplored. The heavy isotopes from 291Mc to
294Mc might also be produced using charged-particle evaporation, in
the 245Cm(48Ca,p'x'n) and 248Cm(48Ca,p'x'n) reactions.
The light isotopes 284Mc, 285Mc, and 286Mc could be made from the
241Am+48Ca reaction. They would undergo a chain of alpha decays,
ending at transactinide isotopes too light to be made by hot fusion
and too heavy to be made by cold fusion. The isotope 286Mc was found
in 2021 at Dubna, in the reaction: it decays into the already-known
282Nh and its daughters. The yet lighter 282Mc and 283Mc could be made
from 243Am+44Ca, but the cross-section would likely be lower.
Other possibilities to synthesize nuclei on the island of stability
include quasifission (partial fusion followed by fission) of a massive
nucleus. Such nuclei tend to fission, expelling doubly magic or nearly
doubly magic fragments such as calcium-40, tin-132, lead-208, or
bismuth-209. It has been shown that the multi-nucleon transfer
reactions in collisions of actinide nuclei (such as uranium and
curium) might be used to synthesize the neutron-rich superheavy nuclei
located at the island of stability, although formation of the lighter
elements nobelium or seaborgium is more favored. One last possibility
to synthesize isotopes near the island is to use controlled nuclear
explosions to create a neutron flux high enough to bypass the gaps of
instability at 258-260Fm and at mass number 275 (atomic numbers 104 to
108), mimicking the r-process in which the actinides were first
produced in nature and the gap of instability around radon bypassed.
Some such isotopes (especially 291Cn and 293Cn) may even have been
synthesized in nature, but would have decayed away far too quickly
(with half-lives of only thousands of years) and be produced in far
too small quantities (about 10−12 the abundance of lead) to be
detectable as primordial nuclides today outside cosmic rays.
Physical and atomic
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In the periodic table, moscovium is a member of group 15, the
pnictogens. It appears below nitrogen, phosphorus, arsenic, antimony,
and bismuth. Every previous pnictogen has five electrons in its
valence shell, forming a valence electron configuration of ns2np3. In
moscovium's case, the trend should be continued and the valence
electron configuration is predicted to be 7s27p3; therefore, moscovium
will behave similarly to its lighter congeners in many respects.
However, notable differences are likely to arise; a largely
contributing effect is the spin-orbit (SO) interaction--the mutual
interaction between the electrons' motion and spin. It is especially
strong for the superheavy elements, because their electrons move much
faster than in lighter atoms, at velocities comparable to the speed of
light. In relation to moscovium atoms, it lowers the 7s and the 7p
electron energy levels (stabilizing the corresponding electrons), but
two of the 7p electron energy levels are stabilized more than the
other four. The stabilization of the 7s electrons is called the
inert-pair effect, and the effect "tearing" the 7p subshell into the
more stabilized and the less stabilized parts is called subshell
splitting. Computation chemists see the split as a change of the
second (azimuthal) quantum number 'l' from 1 to and for the more
stabilized and less stabilized parts of the 7p subshell, respectively.
For many theoretical purposes, the valence electron configuration may
be represented to reflect the 7p subshell split as 7s7p7p. These
effects cause moscovium's chemistry to be somewhat different from that
of its lighter congeners.
The valence electrons of moscovium fall into three subshells: 7s (two
electrons), 7p1/2 (two electrons), and 7p3/2 (one electron). The first
two of these are relativistically stabilized and hence behave as inert
pairs, while the last is relativistically destabilized and can easily
participate in chemistry. (The 6d electrons are not destabilized
enough to participate chemically.) Thus, the +1 oxidation state should
be favored, like Tl+, and consistent with this the first ionization
potential of moscovium should be around 5.58 eV, continuing the trend
towards lower ionization potentials down the pnictogens. Moscovium and
nihonium both have one electron outside a quasi-closed shell
configuration that can be delocalized in the metallic state: thus they
should have similar melting and boiling points (both melting around
400 °C and boiling around 1100 °C) due to the strength of their
metallic bonds being similar. Additionally, the predicted ionization
potential, ionic radius (1.5 Å for Mc+; 1.0 Å for Mc3+), and
polarizability of Mc+ are expected to be more similar to Tl+ than its
true congener Bi3+. Moscovium should be a dense metal due to its high
atomic weight, with a density around 13.5 g/cm3. The electron of the
hydrogen-like moscovium atom (oxidized so that it only has one
electron, Mc114+) is expected to move so fast that it has a mass 1.82
times that of a stationary electron, due to relativistic effects. For
comparison, the figures for hydrogen-like bismuth and antimony are
expected to be 1.25 and 1.077 respectively.
Chemical
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Moscovium is predicted to be the third member of the 7p series of
chemical elements and the heaviest member of group 15 in the periodic
table, below bismuth. Unlike the two previous 7p elements, moscovium
is expected to be a good homologue of its lighter congener, in this
case bismuth. In this group, each member is known to portray the group
oxidation state of +5 but with differing stability. For nitrogen, the
+5 state is mostly a formal explanation of molecules like N2O5: it is
very difficult to have five covalent bonds to nitrogen due to the
inability of the small nitrogen atom to accommodate five ligands. The
+5 state is well represented for the essentially non-relativistic
typical pnictogens phosphorus, arsenic, and antimony. However, for
bismuth it becomes rare due to the relativistic stabilization of the
6s orbitals known as the inert-pair effect, so that the 6s electrons
are reluctant to bond chemically. It is expected that moscovium will
have an inert-pair effect for both the 7s and the 7p1/2 electrons, as
the binding energy of the lone 7p3/2 electron is noticeably lower than
that of the 7p1/2 electrons. Nitrogen(I) and bismuth(I) are known but
rare and moscovium(I) is likely to show some unique properties,
probably behaving more like thallium(I) than bismuth(I). Because of
spin-orbit coupling, flerovium may display closed-shell or noble
gas-like properties; if this is the case, moscovium will likely be
typically monovalent as a result, since the cation Mc+ will have the
same electron configuration as flerovium, perhaps giving moscovium
some alkali metal character. Calculations predict that moscovium(I)
fluoride and chloride would be ionic compounds, with an ionic radius
of about 109-114 pm for Mc+, although the 7p1/2 lone pair on the Mc+
ion should be highly polarisable. The Mc3+ cation should behave like
its true lighter homolog Bi3+. The 7s electrons are too stabilized to
be able to contribute chemically and hence the +5 state should be
impossible and moscovium may be considered to have only three valence
electrons. Moscovium would be quite a reactive metal, with a standard
reduction potential of −1.5 V for the Mc+/Mc couple.
The chemistry of moscovium in aqueous solution should essentially be
that of the Mc+ and Mc3+ ions. The former should be easily hydrolyzed
and not be easily complexed with halides, cyanide, and ammonia.
Moscovium(I) hydroxide (McOH), carbonate (Mc2CO3), oxalate (Mc2C2O4),
and fluoride (McF) should be soluble in water; the sulfide (Mc2S)
should be insoluble; and the chloride (McCl), bromide (McBr), iodide
(McI), and thiocyanate (McSCN) should be only slightly soluble, so
that adding excess hydrochloric acid would not noticeably affect the
solubility of moscovium(I) chloride. Mc3+ should be about as stable as
Tl3+ and hence should also be an important part of moscovium
chemistry, although its closest homolog among the elements should be
its lighter congener Bi3+. Moscovium(III) fluoride (McF3) and
thiozonide (McS3) should be insoluble in water, similar to the
corresponding bismuth compounds, while moscovium(III) chloride
(McCl3), bromide (McBr3), and iodide (McI3) should be readily soluble
and easily hydrolyzed to form oxyhalides such as McOCl and McOBr,
again analogous to bismuth. Both moscovium(I) and moscovium(III)
should be common oxidation states and their relative stability should
depend greatly on what they are complexed with and the likelihood of
hydrolysis.
Like its lighter homologues ammonia, phosphine, arsine, stibine, and
bismuthine, moscovine (McH3) is expected to have a trigonal pyramidal
molecular geometry, with an Mc-H bond length of 195.4 pm and a H-Mc-H
bond angle of 91.8° (bismuthine has bond length 181.7 pm and bond
angle 91.9°; stibine has bond length 172.3 pm and bond angle 92.0°).
In the predicted aromatic pentagonal planar cluster, analogous to
pentazolate (), the Mc-Mc bond length is expected to be expanded from
the extrapolated value of 312-316 pm to 329 pm due to spin-orbit
coupling effects.
Experimental chemistry
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The isotopes 288Mc, 289Mc, and 290Mc have half-lives long enough for
chemical investigation. A 2024 experiment at the GSI, producing 288Mc
via the 243Am+48Ca reaction, studied the adsorption of nihonium and
moscovium on SiO2 and gold surfaces. The adsorption enthalpy of
moscovium on SiO2 was determined experimentally as (68% confidence
interval). Moscovium was determined to be less reactive with the SiO2
surface than its lighter congener bismuth, but more reactive than
closed-shell copernicium and flerovium. This arises because of the
relativistic stabilisation of the 7p1/2 shell.
External links
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* [
http://radiochemistry.org/periodictable/elements/115.html Uut and
Uup Add Their Atomic Mass to Periodic Table]
* [
http://physicsweb.org/articles/world/17/7/7 Superheavy elements]
* [
http://elements.vanderkrogt.net/element.php?sym=Mc History and
etymology]
* [
http://www.periodicvideos.com/videos/115.htm Moscovium] at 'The
Periodic Table of Videos' (University of Nottingham)
License
=========
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http://creativecommons.org/licenses/by-sa/3.0/
Original Article:
http://en.wikipedia.org/wiki/Moscovium
