Tennessine is a synthetic chemical element with the symbol Ts and atomic number 117. It is the second-heaviest known element and the penultimate element of the 7th period of the periodic table. In 2010 Russian and American scientists announced the production of six atoms of tennessine, which were formed when 22 milligrams of berkelium-249 were bombarded with atoms of calcium-48, at the cyclotron at the Joint Institute for Nuclear Research in Dubna, Russia. These atoms were of atomic weights 293 and 294.
It may be located in the “island of stability”, a concept that explains why some superheavy elements are more stable compared to an overall trend of decreasing stability for elements beyond bismuth on the periodic table. The synthesized tennessine atoms have lasted tens and hundreds of milliseconds.
In the periodic table, tennessine is expected to be a member of group 17, all other members of which are halogens. Some of its properties may significantly differ from those of the halogens due to relativistic effects. As a result, tennessine is expected to be a volatile metal that neither forms anions nor achieves high oxidation states. A few key properties, such as its melting and boiling points and its first ionization energy, are nevertheless expected to follow the periodic trends of the halogens.