Meitnerium (109)

Meitnerium is a chemical element with symbol Mt and atomic number 109. It is an extremely radioactive synthetic element (an element not found in nature that can be created in a laboratory). The most stable known isotope, meitnerium-278, has a half-life of 7.6 seconds. The GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany, first created this element in 1982.

The interested reader should consult the on-line version of The Wonderful World of Atoms and Nuclei for a fascinating insight into research on "super-heavy" atoms.

Name: Meitnerium Symbol: Mt Atomic number: 109 Atomic weight: [ 276 ] Standard state: presumably a solid at 298 K CAS Registry ID: 54038-01-6

Group in periodic table: 9 Period in periodic table: 7 Block in periodic table: d-block Color: unknown, but probably metallic and silvery white or grey in appearance Classification: Metallic

Historical information

In August 1982 the first atom of the element meitnerium with atomic number 109 was detected at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany by Peter Armbruster, Gottfried Münzenber and their co-workers. The isotope of element 109 which was discovered has an atomic mass number of 266 (that is, 266 times heavier than hydrogen). The new element was produced by fusing an iron (⁵⁸Fe) and a bismuth atom (²⁰⁹Bi) together in a reaction that produces a neutron. This was achieved by accelerating the iron atoms to a high energy in the heavy ion accelerator UNILAC at GSI.

The naming of meitnerium was discussed in the element naming controversy regarding the names of elements 104 to 109, but meitnerium was the only proposal and thus was never disputed. The name meitnerium (Mt) was suggested in honor of the Austrian physicist Lise Meitner, a co-discoverer of protactinium (with Otto Hahn), and one of the discoverers of nuclear fission. In 1994 the name was recommended by IUPAC, and was officially adopted in 1997. It is thus the only element named specifically after a non-mythological woman

Physical properties

• Predicted Density of solid: 28200 kg m^-3
• Meitnerium is expected to be a noble metal.
• Based on the most stable oxidation states of the lighter group 9 elements, the most stable oxidation states of meitnerium are predicted to be the +6, +3, and +1 states, with the +3 state being the most stable in aqueous solutions. In comparison, rhodium and iridium show a maximum oxidation state of +6, while the most stable states are +4 and +3 for iridium and +3 for rhodium. Group 9 is the first group in the transition metals to show lower oxidation states than the group number, the +9 state not being known for any element. The oxidation state +9 might be possible for meitnerium in the nonafluoride (MtF₉) and the [MtO₄]⁺ cation, although [IrO₄]⁺ is expected to be more stable. The tetrahalides of meitnerium have also been predicted to have similar stabilities to those of iridium, thus also allowing a stable +4 state. 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.

Orbital properties

• Ground state electron configuration:  [Rn].5f¹⁴.6d⁷.7s² (a guess based upon that of iridium)
• Shell structure:  2.8.18.32.32.15.2
• Term symbol:   ⁴F_9/2 (a guess based upon guessed electronic structure)

Isolation

Only a few atoms of element 109, meitnerium, have ever been made. The first atoms were made through a nuclear reaction involving fusion of an isotope of bismuth, ²⁰⁹Bi, with one of iron, ⁵⁸Fe.

²⁰⁹Bi + ⁵⁸Fe → ²⁶⁶Mt + ¹n

Isolation of an observable quantity of meitnerium has never been achieved, and may well never be. This is because meitnerium decays very rapidly through the emission of α-particles.