Ununseptium

Ununseptium is the temporary name of a superheavy artificial chemical element with temporary symbol Uus and atomic number 117. The element, also known as eka-astatine or simply element 117, is the second-heaviest of all the elements that have been reportedly created so far and is the second-to-last element of the 7th period of the periodic table. Its discovery was first announced in 2010—synthesis was claimed in Dubna, Russia, by a joint Russian–American collaboration, thus making it the most recently discovered element. Another experiment in 2011 created one of its daughter isotopes using a different method, partially confirming the results of the discovery experiment, and the original experiment was repeated successfully in 2012. The IUPAC/IUPAP Joint Working Party (JWP), however, has made no comment yet on whether or not the element can be recognized as discovered.

In the periodic table, ununseptium is located in group 17, all previous members of which are halogens. However, the element is likely to have significantly different properties from the halogens, which form the rest of the group, although a few key properties such as melting and boiling points and first ionization energy are expected to follow the periodic trends. While lighter ununseptium isotopes are agreed in the literature to be very unstable, there are signs that some of the heavier ununseptium isotopes may be much more stable.