Atomic Mass- 238

Uranium is a highly radioactive actinide metal. It is the heaviest and last naturally occurring element in the periodic table. Uranium was at one point used in dyes and stains. The most common isotope of uranium is U-238. U-238 also has the longest half life of the Uranium isotopes, at about about 4,468,000,000 years. U-235 was the isotope used in atomic bombs.