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.