High Quality Content by WIKIPEDIA articles! Ununoctium is the temporary IUPAC name for the transactinide element having the atomic number 118 and temporary element symbol Uuo. It is also known as eka-radon or element 118, and on the periodic table of the elements it is a p-block element and the last one of the 7th period. Ununoctium is currently the only synthetic member of Group 18. It has the highest atomic number and highest atomic mass of all the elements discovered so far.