Ununseptium is a placeholder assigned until the element has been given a final name. As of late 2006 it is the only element through 118 whose discovery has not yet been claimed.

the second-heaviest of all the elements that have been 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 directly, partially confirming the results of the discovery experiment, and the original experiment was repeated successfully in 2012. However, the IUPAC/IUPAP Joint Working Party (JWP), which is in charge of examining claims of discovery of superheavy elements, has made no comment yet on whether the element can be recognized as discovered. Once it is so recognized, it may receive a permanent name which will be suggested for the element by its discoverers; "ununseptium" is a temporary systematic element name that is intended to be used before a permanent one is established. It is commonly called "element 117" by researchers and in the literature instead of "ununseptium".