Atomic heavyweight reacts with carbon

For the first time, chemical effects of the relativity theory can be investigated

Graphic representation of a seaborgium hexacarbonyl molecule. © Alexander Yakushev / Christoph E. Düllmann
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Milestone in superheavy chemistry: For the first time, chemists have allowed atoms of the super-heavy element seaborgium to react with carbon atoms. This breakthrough by an international research team now provides clues to the effect of the theory of relativity on chemistry, as the scientists in the journal "Science" report. Connections with even heavier elements should follow in the near future.

At the very end of the periodic table of chemical elements are the atomic heavyweights: the so-called superheavy elements with atomic numbers 104 or more. These elements are extremely difficult to research: they are not found in nature and only a few atoms a day can be produced in particle accelerators. On top of that, these atoms disintegrate again after just a few seconds.

Super difficult to explore

What drives researchers to not only study these super-heavy yet inaccessible elements, but also to carry out chemical reactions with them? The many protons in the atomic nucleus of the superheavy atoms accelerate the orbiting electrons to enormous speeds - up to 80 percent of the speed of light. According to Einstein's theory of relativity, the electrons thereby become heavier when compared to their mass when they are at rest. This mass increase, in turn, should affect their location in the atomic shell and, consequently, their chemical properties. In chemical reactions of these elements, the influence of the theory of relativity on chemistry could be directly investigated.

And that's exactly what scientists around Alexander Yakushev at the Helmholtz Center for Heavy Ion Research in Darmstadt have now achieved: The researchers observed the reaction of 18 atoms of the element seaborgium (elementary symbol Sg, atomic number 106) with carbon monoxide. The result is so-called hexacarbonyl complexes: a single seaborgium atom is surrounded by six molecules of carbon monoxide. It is the first observed reaction of a superheavy atom with a carbon compound.

Ten seconds to break up

However, only about ten seconds to the decay of the seaborgium were sufficient to observe some properties of the complexes generated: the researchers studied the behavior of the volatile complex in the gas phase and its adsorption on a surface of silicon dioxide. display

Scientists connect the chemical apparatus (bottom center) to the so-called separator (top right), where the generated seaborgium is collected. Matthias Sch del

These observations also compared them with the behavior of the lighter elements molybdenum and tungsten, which form similar complexes. Both elements, like seaborgium, belong to the sixth main group of the periodic table and are therefore so-called homologous elements that behave chemically similar. The properties measured on all these elements are consistent with theoretical calculations in which the effects of relativity are taken into account.

Light elements pave the way

The lighter homologous elements also paved the way for the current breakthrough: the scientists conducted their first preparatory experiments with molybdenum to characterize the reaction conditions. The heavy element group around Hiromitsu Haba at the RIKEN Nishina Center in Japan specializes in the production of seaborgium in the particle accelerator. Together with the chemical knowledge succeeded in the synthesis of seaborgium hexacarbonyl.

After this first successful step on the way to more detailed investigations of the super-heavy elements, the team is already plotting plans for further studies of other new compounds, even heavier elements than seaborgium.

(Science, 2014; doi: 10.1126 / science.1255720)

(Johannes Gutenberg University Mainz, 22.09.2014 - AKR)