Meitnerium (Mt)

• Element Symbol: Mt
• Atomic Number: 109
• Atomic Mass: 268
• Group # in Periodic Table: 9
• Group Name: Transition metals
• Period in Periodic Table: 7
• Block of Periodic Table: d-block
• Discovered by: Peter Armbruster, Gottfried Münzenberg (1982)

Meitnerium is a synthetic and highly radioactive element that is not found in nature. Its chemical symbol is Mt, and its atomic number is 109. The electronic configuration is [Rn] 5f¹⁴6d⁷7s². Meitnerium is also known as unnilennium (Une). In the periodic table, it is located in the d-block of period 7 and Group 9, and it falls between hassium and darmstadtium. Meitnerium is a member of the transuranium group. A transuranium element is any element that comes after uranium in the periodic table. Most transuranic elements are radioactive and unstable, with half-lives of only fractions of seconds. The two transuranium elements found in nature include neptunium and plutonium, while the rest—such as meitnerium and many others—are synthetically made.

German scientists Peter Armbruster, Gottfried Münzenber, and their team discovered meitnerium in 1982 at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany. However, the element’s name was recognized only after 1992. Meitnerium was produced by bombarding atoms of bismuth-209 with the ions of iron-58 using a device known as a linear accelerator. This procedure created meitnerium-266 atoms and a free neutron. This isotope has a half-life of 3.8 milliseconds.

Meitnerium was named after the Austrian/Swedish mathematician and physicist Lise Meitner to honor her work in the field of nuclear fission. Meitner is known as the most significant woman scientist of the twentieth century. On November 7, 1878, she was born into a Jewish family in Austria. After receiving her doctorate degree in 1906, she went to Berlin, where she worked with Max Planck and chemist Otto Hahn. The three of them worked together for about thirty years in the field of nuclear fission. In 1923, she discovered the radiationless transition called the Auger effect, and she mentioned this phenomenon in passing when publishing her observations about beta radiation. The physics community thus overlooked her discovery. As a result, the effect was named after a French scientist, Pierre Victor Auger, who independently discovered the effect two years later and wrote a paper that described his observations. In 1938, because she was Jewish, she had to flee to Sweden when Germany captured Austria. In Sweden, she encountered Hahn one more time when they started a new series of investigations. In 1944, Hahn was awarded the Nobel Prize for Chemistry for the research that he had conducted with Meitner, but she was overlooked by the Nobel committee partly because Hahn had downplayed her role ever since she had left Germany. Finally, in 1992, the element 109, which is considered the heaviest element known to the universe, was named meitnerium in Lise Meitner’s honor.

Physical Properties

Meitnerium is classified as a transition metal. Very few atoms of this metal have ever been produced, and its physical properties have never been observed. It is predicted that its properties would be similar to that of iridium, which is immediately above meitnerium in the periodic table, and also rhodium, which is two places above meitnerium in the periodic table. Meitnerium has an atomic weight of 278, and its atomic number is 109. As late as 2016, only one atom could be produced at a time. Meitnerium is presumed to be solid at room temperature, and its boiling and melting points are unknown. Likewise, the element’s standard state—that is, its state at 298 kelvin (K)—as well as its density are unknown. The covalent radius of the atom is about 6–10 picometers, making its radius wider than that of iridium.

Chemical Properties

Meitnerium does not occur naturally; it can be created only in laboratories. Its properties resemble those of the element iridium.

Moreover, it does not have any naturally occurring or stable isotopes. The most stable isotope is meitnerium-278, with a half-life of about 8 seconds. This isotope undergoes decay to form bohrium-274. Eight different isotopes have been found, with atomic masses of 266, 268, 270, and 274 to 278. Heavier isotopes are more stable than their lighter counterparts. Most of these isotopes undergo alpha decay, but some undergo spontaneous fission.

Many unstable atoms experience the radioactive decay known as alpha decay to become more stable. During this process, the nucleus of the atom loses two protons and two neutrons that together are termed the alpha particle. This process causes the element to change, and the larger unstable nucleus turns into a smaller, more stable nucleus. For example, the atom of uranium-92 undergoes alpha decay and turns into thorium-90. In a similar way, meitnerium-278 undergoes alpha decay to form bohrium-274.

Spontaneous fission is another way for an unstable atom to become more stable. In this type of radioactive decay, the unstable nucleus of the element separates into two approximately equal nuclei of lighter elements. Spontaneous fission usually takes place in elements with mass number 230 or more.

Applications

Only very small amounts of meitnerium have ever been produced in laboratories. The element has no uses outside of research. Because it was discovered so late in the twentieth century and because of its very short half-life, meitnerium has proven to be a challenging element to research. However, an experiment has been performed by Paul Dirac, D.R. Hartree, and V.A. Fock. In their experiments, they were attempting to detect the effects of X-ray transitions in meitnerium. The researchers studied the ionization potentials of the K- and L-shells of meitnerium-268, taking into account the quantum electrodynamics and finite nuclear-size effects. They found that a signal was transmitted from the possible K-inversion, and this signal was observed to arise from a nuclear gamma transition.

Bibliography

"Alpha Decay." Glossary. Jefferson Lab, n.d. Web. 26 Jan. 2016.

Duparc, Olivier Hardouin. "Pierre Auger–Lise Meitner: Comparative Contributions to the Auger Effect." Hanser eLibrary.com. Carl Hanser Verlag GmbH & Co. KG, n.d. Web, 26 Jan. 2016.

"The Element Meitnerium." Its Elemental. Jefferson Lab, n.d. Web. 26 Jan. 2016.

Greenwood, Norman N, and Alan Earnshaw. Chemistry of the Elements. 2nd ed. Portsmouth: Butterworth-Heinemann, 1997. Print.

"Lise Meitner (1878-1968)." atomicarchive.com. AJ Software & Multimedia, n.d. Web. 26 Jan. 2016.

"Meitnerium." Columbia Electronic Encyclopedia. 6th ed. Questia, 2015. Web. 26 Jan. 2016.

"Meitnerium." Periodic Table. Royal Society of Chemistry, n.d. Web. 26 Jan. 2016.

"Meitnerium (Mt)." Encyclopaedia Britannica. Encyclopaedia Britannica, Inc., n.d. Web. 26 Jan. 2016.

Seaborg, Glenn T. "Transuranium element." Encyclopedia Britannica. Encyclopaedia Britannica, Inc., n.d. Web. 27 Jan. 2016. <http://www.britannica.com/science/transuranium-element>.

"Spontaneous fission." Encylopaedia Britannica. Encyclopaedia Britannica, Inc., n.d. Web. 26 Jan. 2016. <http://www.britannica.com/science/spontaneous-fission>.

Thierfelder C., P. Schwerdtfeger, F. Heßberger, and S. Hofmann. "Dirac-Hartree-Fock Studies of X-ray Transitions in Meitnerium." The European Physical Journal A 36.2 (May 2008): 227-31. SocietàItaliana di Fisica. Web. 26 Jan. 2016.

<https://www.researchgate.net/publication/225455631‗Dirac-Hartree-Fock‗studies‗of‗X-ray‗transitions‗in‗meitnerium>.