4046 Uranium Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with symbol U and atomic number 92. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weakly radioactive because all its isotopes are unstable (with half-lives of the 6 naturally known isotopes, U-233 - U-238, varying between 69 years and 4л_ billion years). The most common isotopes of uranium are uranium-238 (which has 146 neutrons and accounts for almost 99.3% of the uranium found in nature) and uranium-235 (which has 143 neutrons, accounting for 0.7% of the element found naturally). Uranium has the second highest atomic weight of the primordially occurring elements, lighter only than plutonium. Its density is about 70% higher than that of lead, but not as dense as gold or tungsten. It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite. 60101674 U White powder. 1, carcinogenic to humans. (L135) 2014-08-29T04:48:45Z 2026-04-06T04:25:12Z true [U] U InChI=1S/U JFALSRSLKYAFGM-UHFFFAOYSA-N 238.0289 238.050782583 Exogenous Solid CHEM002952 DTXSID1042522 NS00099729 0.0 0.0 1.7784 0 0 0 0 0