meitnerium

hassium ← meitnerium → darmstadtium Ir ↑ Mt ↓ (Upe) 109Mt Periodic table
Appearance
probably light silver green metallic
General properties
Name, symbol, number	meitnerium, Mt, 109
Element category	transition metal
Group, period, block	9, 7, d
Standard atomic weight	[276] g·mol−1
Electron configuration	perhaps [Rn] 5f14 6d7 7s2 (guess based on iridium)
Electrons per shell	2, 8, 18, 32, 32, 15, 2 (Image)
Physical properties
Phase	solid (presumably)
Atomic properties
Miscellanea
CAS registry number	54038-01-6
Most stable isotopes
Main article: Isotopes of meitnerium
iso NA half-life DM DE (MeV) DP 276Mt syn 0.72 s α 9.71 272Bh 275Mt syn 9.7 ms α 10.33 271Bh 274Mt syn 0.44 s α 9.76 270Bh 270mMt ? syn 1.1 s α 266Bh 270gMt syn 5 ms α 10.03 266Bh 268Mt syn 42 ms α 10.26,10.10 264Bh 266Mt syn 1.7 ms α 11.00 262Bh
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Meitnerium (pronounced /maɪtˈnɛəriəm/ ( listen) myet-NAIR-ee-əm or /maɪtˈnɜriəm/ myet-NER-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, unlike its lighter neighbours.

It was first synthesized in 1982 and the most stable isotope known is Mt-276, with a half-life of ~700 ms, although a possible isomer of the isotope Mt-270 has an apparent half-life ~1.1 s.

History

Official discovery

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.^[1] The team bombarded a target of bismuth-209 with accelerated nuclei of iron-58 and detected a single atom of the isotope meitnerium-266:

20983Bi + 5826Fe → 266109Mt + n

Naming

Historically, element 109 has been referred to as eka-iridium.

The name meitnerium (Mt) was suggested in honor of the Austrian physicist Lise Meitner. In 1997, the name was officially adopted by the IUPAC.

Future experiments

The team at RIKEN, Japan, have indicated that as part of their ongoing studies using ²⁴⁸Cm targets, they may study the new reaction ²⁴⁸Cm(²⁷Al,xn) in the future.

Isotopes and nuclear properties

Nucleosynthesis

Target-Projectile Combinations leading to Z=109 compound nuclei

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with Z=109.

Cold fusion

This section deals with the synthesis of nuclei of meitnerium by so-called "cold" fusion reactions. These are processes which create compound nuclei at low excitation energy (~10-20 MeV, hence "cold"), leading to a higher probability of survival from fission. The excited nucleus then decays to the ground state via the emission of one or two neutrons only.

²⁰⁹Bi(⁵⁸Fe,xn)^267-xMt (x=1)

The first success in this reaction was in 1982 by the GSI team in their discovery experiment with the identification of a single atom of ²⁶⁶Mt in the 1n neutron evaporation channel.^[1] The GSI team used the parent-daughter correlation technique. After an initial failure in 1983, in 1985 the team at the FLNR, Dubna, observed alpha decays from the descendant ²⁴⁶Cf indicating the formation of meitnerium. The GSI synthesised a further 2 atoms of ²⁶⁶Mt in 1988 and continued in 1997 with the detection of 12 atoms during the measurement of the 1n excitation function. ^{[2] [3]}

²⁰⁸Pb(⁵⁹Co,xn)^267-xMt (x=1)

This reaction was first studied in 1985 by the team in Dubna. They were able to detect the alpha decay of the descendant ²⁴⁶Cf nuclei indicating the formation of meitnerium atoms. In 2007, in a continuation of their study of the effect of odd-Z projectiles on yields of evaporation residues in cold fusion reactions, the team at LBNL synthesised ²⁶⁶Mt and were able to correlate the decay with known daughters.^[4]

¹⁸¹Ta(⁸⁶Kr,xn)^267-xMt

There are indications that this cold fusion reaction using a tantalum target was attempted in August 2001 at the GSI. No details can be found suggesting that no atoms of meitnerium were detected.

Hot fusion

²³⁸U(³⁷Cl,xn)^275-xMt

In 2002-2003, the team at LBNL attempted the above reaction in order to search for the isotope ²⁷¹Mt with hope that it may be sufficiently stable to allow a first study of the chemical properties of meitnerium. Unfortunately, no atoms were detected and a cross section limit of 1.5 pb was measured for the 4n channel at the projectile energy used. ^[5]

²⁵⁴Es(²²Ne,xn)^276-xMt

Attempts to produce long-living isotopes of meitnerium were first performed by Ken Hulet at the Lawrence Livermore National Laboratory (LLNL) in 1988 using the asymmetric hot fusion reaction above. They were unable to detect any product atoms and established a cross section limit of 1 nb.^[6]

As a decay product

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

Chronology of isotope discovery

Nuclear isomerism

²⁷⁰Mt

Two atoms of ²⁷⁰Mt have been identified in the decay chains of ²⁷⁸113. 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 yields of isotopes

Cold Fusion

The table below provides cross-sections and excitation energies for cold fusion reactions producing meitnerium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.

Theoretical calculations

Evaporation residue cross sections

The below table contains various targets-projectile combinations for which calculations have provided estimates for cross section yields from various neutron evaporation channels. The channel with the highest expected yield is given.

HIVAP = heavy-ion vaporisation statistical-evaporation model; σ = cross section

Chemical properties

Electronic structure

Extrapolated chemical properties

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 more than Ir which is already the most corrosion resistant metal.

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.

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 whilst 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.

References

External links

• WebElements.com: Meitnerium