What is "ununseptium"

n. The systematic element name for the chemical element with atomic number 117 (''symbol'' Uus)

Ununseptium is a superheavy artificial chemical element with an atomic number of 117 and a temporary symbol of Uus. Also known as eka- astatine or element 117, it is the second-heaviest known element and penultimate element of the 7th period of the periodic table. , fifteen ununseptium atoms have been observed: six when it was first synthesized in 2010, seven in 2012, and two in 2014.

The discovery of ununseptium was announced in Dubna, Russia, by a Russian–American collaboration in 2010, which makes it the most recently discovered element . One of its daughter isotopes was created directly in 2011, partially confirming the results of the experiment. The experiment itself was repeated successfully by the same collaboration in 2012 and by a joint German–American team in 2014. In 2015, the Joint Working Party of the International Union of Pure and Applied Chemistry and the International Union of Pure and Applied Physics, which evaluates claims of discovery of new elements, has recognized the element and assigned the priority to the Russian–American team. In June 2016, the IUPAC published a declaration stating that the discoverers suggested a name of tennessine ( or ), symbol Ts, named after Tennessee, United States . The name is set to be formally accepted in or after November 2016. "Ununseptium" is a temporary systematic element name formed from Latin roots "one", "one", and "seven"; it is intended to be used until a permanent one is assigned. The working name "element 117" is commonly used by researchers and in the literature.

Ununseptium 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 lead on the periodic table. The synthesized ununseptium atoms have lasted tens and hundreds of milliseconds. In the periodic table, ununseptium is expected to be a member of group 17, all other members of which are halogens. Some of its properties are likely to be significantly different from those of the halogens due to relativistic effects. Unlike the halogens, ununseptium is likely to neither commonly form anions nor achieve 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.