Product Code Database
Meitnerium is a synthetic chemical element; it has Chemical symbol Mt and atomic number 109. It is an extremely radioactive synthetic element (an element not found in nature, but can be created in a laboratory). The most stable known isotope, meitnerium-278, has a half-life of 4.5 seconds, although the unconfirmed meitnerium-282 may have a longer half-life of 67 seconds. The element was first synthesized in August 1982 by the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany, and it was named after Lise Meitner in 1997.
In the periodic table, meitnerium is a d-block transactinide element. It is a member of the 7th period and is placed in the group 9 elements, although no chemical experiments have yet been carried out to confirm that it behaves as the heavier homologue to iridium in group 9 as the seventh member of the 6d series of . Meitnerium is calculated to have properties similar to its lighter homologues, cobalt, rhodium, and iridium.
This work was confirmed three years later at the Joint Institute for Nuclear Research at Dubna (then in the Soviet Union).
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 by the GSI team in September 1992 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 (curium being named for both Pierre Curie and Marie Curie)."Meitnerium is named for the Austrian physicist Lise Meitner." in Meitnerium in Royal Society of Chemistry – Visual Element Periodic Table . Retrieved August 14, 2015.
The isotope 277Mt, created as the final decay product of 293Ts for the first time in 2012, was observed to undergo spontaneous fission with a half-life of 5 milliseconds. Preliminary data analysis considered the possibility of this fission event instead originating from 277Hs, for it also has a half-life of a few milliseconds, and could be populated following undetected electron capture somewhere along the decay chain. This possibility was later deemed very unlikely based on observed decay energy of 281Ds and 281Rg and the short half-life of 277Mt, although there is still some uncertainty of the assignment. Regardless, the rapid fission of 277Mt and 277Hs is strongly suggestive of a region of instability for superheavy nuclei with neutron number = 168–170. The existence of this region, characterized by a decrease in fission barrier height between the deformed shell closure at N = 162 and spherical shell closure at N = 184, is consistent with theoretical models.
Prediction of the probable chemical properties of meitnerium has not received much attention recently. Meitnerium is expected to be a noble metal. The standard electrode potential for the Mt3+/Mt couple is expected to be 0.8 V. 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 . 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. The oxidation state +9, represented only by iridium in IrO4+, might be possible for its congener meitnerium in the nonafluoride (MtF9) and the MtO4+ cation, although IrO4+ is expected to be more stable than these meitnerium compounds. 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.
Theoreticians have predicted the covalent radius of meitnerium to be 6 to 10 pm larger than that of iridium. The atomic radius of meitnerium is expected to be around 128 pm.
The Lawrence Berkeley National Laboratory attempted to synthesize the isotope 271Mt in 2002–2003 for a possible chemical investigation of meitnerium, because it was expected that it might be more stable than nearby isotopes due to having 162 , a magic number for deformed nuclei; its half-life was predicted to be a few seconds, long enough for a chemical investigation. However, no atoms of 271Mt were detected;Zielinski P. M. et al. (2003). "The search for 271Mt via the reaction 238U + 37Cl" , GSI Annual report. Retrieved on 2008-03-01 this isotope of meitnerium is currently unknown.
An experiment determining the chemical properties of a transactinide would need to compare a compound of that transactinide with analogous compounds of some of its lighter homologues: for example, in the chemical characterization of hassium, hassium tetroxide (HsO4) was compared with the analogous osmium compound, osmium tetroxide (OsO4). In a preliminary step towards determining the chemical properties of meitnerium, the GSI attempted sublimation of the rhodium compounds rhodium(III) oxide (Rh2O3) and rhodium(III) chloride (RhCl3). However, macroscopic amounts of the oxide would not sublimate until 1000 °C and the chloride would not until 780 °C, and then only in the presence of carbon aerosol particles: these temperatures are far too high for such procedures to be used on meitnerium, as most of the current methods used for the investigation of the chemistry of superheavy elements do not work above 500 °C.
Following the 2014 successful synthesis of seaborgium hexacarbonyl, Sg(CO)6, studies were conducted with the stable transition metals of groups 7 through 9, suggesting that carbonyl formation could be extended to further probe the chemistries of the early 6d transition metals from rutherfordium to meitnerium inclusive. Nevertheless, the challenges of low half-lives and difficult production reactions make meitnerium difficult to access for radiochemists, though the isotopes 278Mt and 276Mt are long-lived enough for chemical research and may be produced in the decay chains of 294tennessine and 288moscovium respectively. 276Mt is likely more suitable, since producing tennessine requires a rare and rather short-lived berkelium target. (2013). 9783642374661, Springer Science & Business Media. ISBN 9783642374661 The isotope 270Mt, observed in the decay chain of 278Nh with a half-life of 0.69 seconds, may also be sufficiently long-lived for chemical investigations, though a direct synthesis route leading to this isotope and more precise measurements of its decay properties would be required.
|
|
