Meitnerium

2008/9 Schools Wikipedia Selection. Related subjects: Chemical elements

109 hassium ← meitnerium → darmstadtium Ir ↑ Mt ↓ (Upe) Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	meitnerium, Mt, 109
Chemical series	transition metals
Group, Period, Block	9, 7, d
Appearance	unknown, probably silvery white or metallic gray
Standard atomic weight	[270]  g·mol−1
Electron configuration	perhaps [Rn] 5f14 6d7 7s2 (guess based on iridium)
Electrons per shell	2, 8, 18, 32, 32, 15, 2
Phase	presumably a solid
CAS registry number	54038-01-6
Selected 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
References

Meitnerium (pronounced /maɪtˈnɜriəm/) is a chemical element in the periodic table that has the symbol Mt and atomic number 109.

Mt is a synthetic element whose most stable known isotope, Mt-278, has a half-life of half an hour.

Discovery profile

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:

Proposed names

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

The name meitnerium (Mt) was suggested in honour of the Austrian physicist and mathematician Lise Meitner, but there was an element naming controversy as to what the elements from 101 to 109 were to be called; thus IUPAC adopted unnilennium (/ˌjuːnɪˈlɛniəm/ or /ˌʌːnɪˈlɛniəm/, symbol Une) as a temporary, systematic element name. In 1997, however, the dispute was resolved and the current name was adopted.

Electronic structure

Meitnerium is element 109 in the Periodic Table. The two forms of the projected electronic structure are:

Bohr model: 2, 8, 18, 32, 32, 15, 2

Quantum mechanical model: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰ 4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰ 6p⁶7s²5f¹⁴6d⁷

Extrapolated chemical properties of eka-iridium/dvi-rhodium

Oxidation states

Element 109 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 are the first to show lower oxidation states and the +IX state is not known. The latter two members of the group show a maximum oxidation state of +VI, whilst the most stable states are +IV and +III for iridium and +III for rhodium. Meitnerium is therefore expected to form a stable +III state but may also portray stable +IV and +VI states.

Chemistry

The +VI state 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 +VI state becomes more stable as the group is descended. In combination with oxygen, rhodium forms Rh₂O₃ whilst iridium is oxidised to the +IV state in IrO₂. Meitnerium may therefore show a dioxide MtO₂ if eka-iridium reactivity is shown. The +III state is common in the trihalides (not fluorides) formed by direct reaction with halogens. Meitnerium should therefore form MtCl₃, MtBr₃ and MtI₃ in an analogous manner to iridium.

History of synthesis of isotopes in cold fusion

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. 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.

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.

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.

History of synthesis by hot fusion reactions

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.

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.

Synthesis of isotopes as decay products

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

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 represents maxima derived from excitation function measurements. + represents an observed exit channel.

Isomerism in meitnerium nuclides

²⁷⁰Mt

Two atoms of ²⁷⁰Mt have been identified in the decay chains of ²⁷⁸113. The two decays have very different lifetimes and decay energiesand 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 ans 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.