Meitnerium

hassium ← meitnerium → darmstadtium Ir ↑ Mt ↓ (Upe) 109Mt Periodic table
Appearance
unknown
General properties
Name, symbol, number	meitnerium, Mt, 109
Pronunciation	/maɪtˈnɪəriəm/ myet-neer-ee-əm or /maɪtˈnɜriəm/ myet-nur-ee-əm
Element category	unknown
Group, period, block	9, 7, d
Standard atomic weight	[278]
Electron configuration	[Rn] 7s2 5f14 6d7 (calculated)
Electrons per shell	2, 8, 18, 32, 32, 15, 2 (predicted) (Image)
Physical properties
Phase	solid ([citation needed]presumably)
Atomic properties
Oxidation states	3, 4 (a guess based on that of iridium)
Miscellanea
CAS registry number	54038-01-6
Most stable isotopes
Main article: Isotopes of meitnerium
iso NA half-life DM DE (MeV) DP 278Mt syn 7.6 s α 9.6 274Bh 276Mt syn 0.72 s α 9.71 272Bh 274Mt syn 0.44 s α 9.76 270Bh 270mMt ? syn 1.1 s α 266Bh

Meitnerium ( /maɪtˈnɪəriəm/ myt-neer-ee-əm or /maɪtˈnɜriəm/ myt-nur-ee-əm) is a chemical element with the symbol Mt and atomic number 109. It is placed as the heaviest member of group 9 (or VIII) in the periodic table but a sufficiently stable isotope is not known at this time which would allow chemical experiments to confirm its position as a heavier homologue to iridium, unlike its lighter neighbours.

It was first synthesized in 1982 and several isotopes are currently known. The heaviest and the most stable isotope known is ²⁷⁸Mt, with a half-life of ~8 s.

History

Meitnerium was first synthesized on August 29, 1982 by a German research team led by Peter Armbruster and Gottfried Münzenberg at the Institute for Heavy Ion Research (Gesellschaft für Schwerionenforschung) in Darmstadt. The team bombarded a target of bismuth-209 with accelerated nuclei of iron-58 and detected a single atom of the isotope meitnerium-266:

209
83Bi + 58
26Fe → 266
109Mt + n

Meitnerium was formerly known as Unnilennium, bearing the symbol Une. Historically, meitnerium has been referred to as eka-iridium. The name meitnerium (Mt) was suggested in honor of the Austrian physicist Lise Meitner, the discoverer of protactinium. In 1997, the name was officially adopted by the IUPAC.

Nucleosynthesis

Main article: Isotopes of meitnerium

Super-heavy elements such as meitnerium are produced by bombarding lighter elements in particle accelerators that induces fusion reactions. Whereas most of the isotopes of meitnerium can be synthesized directly this way, some heavier ones have only been observed as decay products of elements with higher atomic numbers.

After the first successful reaction of meitnerium in 1982 by the GSI team, a team at FLNR, Dubna, also tried to observe the new element by bombarding bismuth-209 with iron-58. In 1985 they managed to identity alpha decays from the descendant isotope ²⁴⁶Cf indicating the formation of meitnerium. The observation of a further two atoms of ²⁶⁶Mt from the same reaction was reported in 1988 and of another 12 in 1997 by the German team at GSI.

The same meitnerium isotope was also observed by the Russian team at Dubna in 1985 from the reaction:

208
82Pb + 59
27Co → 266
109Mt + n

by detecting the alpha decay of the descendant ²⁴⁶Cf nuclei. In 2007, an American team at LBNL confirmed the decay chain of ²⁶⁶Mt isotope from this reaction.

A different reaction using tantalum-181 and krypton-86 was attempted in August 2001 at the GSI, but no evidence for formation of meitnerium via fusion could be observed.^{[citation needed]} In 2002–2003, the team at LBNL attempted to generate the isotope ²⁷¹Mt to study the chemical properties by bombarding uranium-238 with chlorine-37, but without success. Other long-lived isotopes were unsuccessfully targeted by a team at Lawrence Livermore National Laboratory (LLNL) in 1988 by bombarding einsteinium-254 with neon-22.

Isotopes of meitnerium have also been detected in the decay of heavier elements. Observations to date are shown in the table below:

Evaporation residue	Observed Mt isotope
294Uus	278Mt
288Uup	276Mt
287Uup	275Mt
282Uut	274Mt
278Uut	270Mt
272Rg	268Mt

Isotopes

List of meitnerium isotopes

Isotope	Half-life	Decay mode	Discovery year	Reaction
266Mt	1.7 ms	α	1982	209Bi(58Fe,n)
268Mt	21 ms	α	1994	272Rg(—,α)
270Mt	5.0 ms	α	2004	278Uut(—,2α)
274Mt	0.44 s	α, SF	2006	237Np(48Ca,3n)
275Mt	9.7 ms	α	2003	287Uup(—,3α)
276Mt	0.72 s	α, SF	2003	243Am(48Ca,3n)
278Mt	8 s	α	2009	249Bk(48Ca,3n)

Only seven isotopes of meitnerium have been reported in the research literature. The longest lived one is ²⁷⁸Mt with a half-time of 8 seconds. A metastable nuclear isomer ^270mMt has been reported to also have a half-life of over a second. Isotopes ²⁷⁶Mt and ²⁷⁴Mt have a half-life of 0.72 and 0.44 seconds respectively. The remaining four isotopes have a half life between 1 and 20 milliseconds. The isotope ²⁸¹Mt has been predicted to be the most likely stable one towards β-decay.

Nuclear isomerism

²⁷⁰Mt

Two atoms of ²⁷⁰Mt have been identified in the decay chains of ²⁷⁸Uut. The two decays have very different lifetimes and decay energies and are also produced from two apparently different isomers in ²⁷⁴Rg. The first isomer decays by emission of an 10.03 MeV alpha particle with a lifetime 7.2 ms. The other decays by emitting an alpha particle with a lifetime of 1.63 s. An assignment to specific levels is not possible with the limited data available. Further research is required.

²⁶⁸Mt

The alpha decay spectrum for ²⁶⁸Mt appears to be complicated from the results of several experiments. Alpha lines of 10.28,10.22 and 10.10 MeV have been observed. Half-lives of 42 ms, 21 ms and 102 ms have been determined. The long-lived decay is associated with alpha particles of energy 10.10 MeV and must be assigned to an isomeric level. The discrepancy between the other two half-lives has yet to be resolved. An assignment to specific levels is not possible with the data available and further research is required.

Chemical properties

Unambiguous determination of chemical character of meitnerium has yet to have been established due to two reasons: lack of sufficiently long-lived isotope, and a limited amount of likely volatile compounds that could be studies on a very small scale. However, the IrF₆ fluoride is volatile above 60 ºC and therefore the identical compound of meitnerium might also be sufficiently volatile. However, since the element 112 has been shown to be a transition metal, it is expected that all the elements in the 104–111 range would form an inclusive form a fourth transition metal series, with meitnerium as part of the platinum group elements. Only extrapolated chemical properties are available for meitnerium.

Physical properties

Mt should be a very heavy metal with a density around 30 g/cm³ (Co: 8.9, Rh: 12.5, Ir: 22.5) and a high melting point around 2600–2900°C (Co: 1480, Rh: 1966, Ir: 2454). It should be very corrosion-resistant; even more so than Ir which is currently the most corrosion-resistant metal known.

Oxidation states

Meitnerium is projected to be the sixth member of the 6d series of transition metals and the heaviest member of group 9 in the Periodic Table, below cobalt, rhodium and iridium. This group of transition metals is the first to show lower oxidation states and the +9 state is not known. The latter two members of the group show a maximum oxidation state of +6, whilst the most stable states are +4 and +3 for iridium and +3 for rhodium. Meitnerium is therefore expected to form a stable +3 state but may also portray stable +4 and +6 states.^{[citation needed]} The oxidation state +9 might also be possible for meitnerium.

Chemistry

The +VI state in group 9 is known only for the fluorides which are formed by direct reaction. Therefore, meitnerium should form a hexafluoride, MtF₆. This fluoride is expected to be more stable than iridium(VI) fluoride, as the +6 state becomes more stable as the group is descended.

In combination with oxygen, rhodium forms Rh₂O₃ whereas iridium is oxidised to the +4 state in IrO₂. Meitnerium may therefore show a dioxide, MtO₂, if eka-iridium reactivity is shown.

The +3 state in group 9 is common in the trihalides (except fluorides) formed by direct reaction with halogens. Meitnerium should therefore form MtCl₃, MtBr₃ and MtI₃ in an analogous manner to iridium.