Tennessine

Tennessine occupies the second-to-last slot on the periodic table, sitting below astatine in Group 17. As a halogen it should be reactive and volatile, but relativistic effects bend the rules — theoretical models suggest tennessine may instead be a solid with metallic character. First made in 2010 through an international collaboration, it briefly existed in a detector before decaying away, leaving only its fingerprint in alpha-particle data.

Tennessine serves no practical purpose outside of fundamental research. Each atom decays within milliseconds, making any application impossible. Scientists study it to probe the boundaries of the nuclear shell model, to test relativistic quantum chemistry predictions, and to map the island of stability — a theoretical region where superheavy nuclei might survive longer than current elements allow.

Tennessine was first synthesized in 2010 at the Joint Institute for Nuclear Research in Dubna, Russia, through a collaboration involving JINR, Oak Ridge National Laboratory, and Vanderbilt University. Researchers bombarded californium-249 targets with calcium-48 ions, producing a handful of atoms of element 117. The discovery required years of preparing the rare californium target material at Oak Ridge before experiments could begin. IUPAC verified the discovery in 2016 and approved the name tennessine — symbol Ts — that same year, recognizing Tennessee's contributions to nuclear science through Oak Ridge and Vanderbilt.

Tennessine does not occur in nature and has no known natural sources. Its most stable confirmed isotope, Ts-294, has a half-life of roughly 51 milliseconds, far too short for any primordial atoms to persist. All tennessine atoms must be manufactured in a particle accelerator by nuclear fusion, and only a few dozen have ever been detected.

No tennessine compounds have been created or observed. The element's near-instantaneous decay makes experimental chemistry completely out of reach with today's technology. Computational chemists predict that relativistic effects will suppress tennessine's reactivity compared to lighter halogens, possibly allowing it to form stable compounds with certain noble gases — a behavior that would be extraordinary for any halogen.

• Tennessine is named after the state of Tennessee, recognizing the contributions of Oak Ridge National Laboratory and Vanderbilt University — making it one of the few elements named after a U.S. state.
• Producing tennessine required californium-249, an extremely rare isotope that took years to accumulate at Oak Ridge National Laboratory before the synthesis experiments could even begin.
• Despite being a halogen like fluorine and chlorine, tennessine is predicted to be a solid at room temperature rather than a gas, and may behave more like a post-transition metal than a classic reactive nonmetal.
• Tennessine was the second-to-last element added to the periodic table, with only oganesson (Z=118) discovered at roughly the same time before the table was considered complete through element 118.
• The half-life of Ts-294 is about 51 milliseconds, meaning that if you could somehow hold an atom of tennessine, it would almost certainly be gone before a single heartbeat passed.