Nihonium

Nihonium, element 113, is a post-transition metal predicted to sit below thallium in Group 13, with an electron configuration of [Rn] 5f14 6d10 7s2 7p1. Relativistic effects are expected to make the outermost 7p electron unusually tightly bound, potentially giving nihonium a lower chemical reactivity than thallium and different oxidation state preferences. Its most studied isotope, Nh-286, decays by alpha emission with a half-life measured in seconds. Like all superheavy elements beyond oganesson, nihonium is known only from a small number of observed decay chains recorded at particle accelerators.

Nihonium serves the scientific community as a test case for relativistic quantum chemistry in Group 13, where the transition from lighter homologs such as indium and thallium to seventh-period chemistry is expected to be dramatic. Researchers at RIKEN continue to study its nuclear decay properties to refine models of superheavy nuclear structure. No practical application has been identified, and the element's short lifetime and vanishingly small production rate make any application impossible with current technology.

The synthesis of nihonium was accomplished at the RIKEN Nishina Center for Accelerator-Based Science in Wako, Japan, where Kosuke Morita led a team bombarding bismuth-209 targets with zinc-70 beams. The first confirmed decay chain attributed to element 113 was observed on July 23, 2004, but international recognition required additional confirming events over the following decade. RIKEN reported a third decay chain in 2012 that was deemed unambiguous. IUPAC and IUPAP formally recognized the RIKEN team's priority in December 2015, making this the first element whose discovery was credited to an Asian institution. The team proposed the name nihonium, derived from Nihon, the Japanese word for Japan, and IUPAC approved the name and symbol Nh in November 2016.

Nihonium is purely synthetic and does not occur in nature. Every atom of element 113 that has ever existed was created by a nuclear fusion reaction inside a particle accelerator. The synthesis cross-section for the bismuth-209 plus zinc-70 reaction is extraordinarily small — on the order of tens of femtobarns — meaning the team had to process roughly 100 billion billion beam particles over nine years to accumulate the handful of events needed to confirm discovery.

No compounds of nihonium have been isolated or characterized. Theoretical chemistry predicts that Nh+ would be the most stable ionic form, with the 7p1 valence electron relatively easy to remove, and that nihonium hydride (NhH) and nihonium fluoride (NhF) might be stable gas-phase species. Gas-phase chemical studies have been proposed as a follow-up to the nuclear discovery, aiming to measure adsorption enthalpies and compare them with predictions from relativistic density functional theory.

• The RIKEN team required approximately nine years of continuous accelerator experiments, running the beam for more than 553 days total, before accumulating the three confirmed decay chains needed to claim discovery.
• Nihonium is the first element whose discovery is credited to a research group outside Europe, Russia, or the United States, marking a landmark shift in the geography of superheavy element science.
• The name nihonium comes from Nihon, one of the Japanese words for Japan, meaning the element's very name encodes the national pride and institutional persistence behind its discovery.
• Each synthesis attempt produces element 113 by fusing zinc-70 into bismuth-209, but the reaction succeeds only about once in every 100 quintillion collisions, requiring the world's most intense heavy-ion beams to work.
• Nihonium's predicted electron configuration places one electron in the 7p shell, which relativistic calculations suggest is contracted and stabilized so strongly that nihonium's chemistry may differ more from thallium than thallium differs from indium.