Ununseptium (Uus) is the latest element to have been synthesized; much of the data are theoretical. It has no stable isotopes. A standard atomic mass cannot be given.
* Values marked # are not purely derived from experimental data, but at least partly from systematic trends.
1. ^ a b Yu. Ts. Oganessian et al., Synthesis of a New Element with Atomic Number Z=117, Phys. Rev. Lett. 104, 142502 (2010). DOI: 10.1103/PhysRevLett.104.142502.
* Isotope masses from Ame2003 Atomic Mass Evaluation: G. Audi, O. Bersillon, J. Blachot, A.H. Wapstra, The Nubase evaluation of nuclear and decay properties, Nucl. Phys. A729 (2003) 3-128.