Nihonium

For more than two hundred years, all periodic table elements were discovered exclusively in Europe, the United States or Russia. In 2015, IUPAC officially credited the Japanese RIKEN institute team with the discovery of element 113. Named 'nihonium' (symbol Nh, from Nihon, 'the land of the rising sun'), it was a historic milestone of global scientific prestige for Japanese science and for the entire Asian continent.

In lighter group 13 elements such as aluminum, the +3 state is universal. However, in period 7, relativistic effects cause the 7s² subshell contraction and inert closure and divide the 7p subshell. Removing the two 7s electrons would require exorbitant energy; therefore nihonium loses exclusively its lone 7p₁/₂ electron, showing a very stable monovalent (+1) chemistry similar to thallium or silver.

The acid test in superheavy physics consists of the newborn atom emitting successive alpha particles until reaching a previously known nuclide. The third nihonium atom obtained at RIKEN in 2012 decayed alpha six times in a row, transmuting into roentgenium, meitnerium, bohrium, dubnium and finally mendelevium-254. This perfect and uninterrupted chain connected element 113 with well-cataloged nuclides, clearing any doubt about its authenticity.

The zinc-70 on bismuth reaction cross section was barely thirty femtobarns, an almost null probability. Keeping a giant linear accelerator running 24 hours a day for months required millimetric thermal control of the bismuth target (which melts at only 271 °C) and extreme vacuum stability. The semiconductor detector had to register millions of parasitic collisions per second without saturating until capturing the atom on August 12, 2012.

Nihonium creation is extremely improbable: very few atoms are produced even after long accelerator experiments. To confirm a discovery, scientists must register enough decay signals and demonstrate that they correspond to the new element, ruling out other explanations. That combination of scarce production, short lives and need for solid evidence made confirmation require years of work.

In experiments at Dubna and RIKEN, nihonium-284 atoms were dragged by helium gas over a matrix of gold-coated silicon detectors. Unlike volatile copernicium, the nihonium atom deposited at temperatures close to room temperature, demonstrating that it forms a stronger metallic adsorption bond on gold. This confirmed that by incorporating an electron into the 7p orbital, typical metallic reactivity is partially recovered.

Nihonium is in group 13, below thallium and aluminum. Due to its position in the periodic table, metallic character is expected, but its electrons may behave differently due to its large atomic mass. Models predict that it will not exactly resemble aluminum and that some of its properties will be closer to those of heavy metals. Experimental information remains limited.