![Uranium element card: symbol U, atomic number 92, atomic mass 238.03, electron configuration [Rn] 5f³ 6d¹ 7s², oxidation states +6, Actinide, f-block, period 7, solid at room temperature.](https://stage.chemistry-dictionary.com/wp-content/uploads/2026/09/uranium-chemical-element.webp)
Uranium is a dense, reactive metal prominently located in the actinide series. It slowly reacts with ambient air to accumulate a dark, protective layer of uranium oxide. Uranium is fairly abundant throughout the Earth’s rocky crust.
Miners routinely discover it in widespread mineral deposits like uraninite and pitchblende. Massive total quantities of uranium are also dissolved within the global oceans. Uranium is most famous for its unique and powerful nuclear properties.
The rare uranium-235 isotope can independently sustain a continuous nuclear fission chain reaction. Fission occurs when a heavy nucleus violently splits into lighter elemental fragments. If slow neutrons bombard a uranium-235 nucleus, it splits into lighter elements.
This violent split releases huge amounts of thermal energy alongside additional neutrons. These newly released neutrons can then strike and split other nearby uranium atoms. Chemically, uranium exhibits multiple complex oxidation states ranging from +3 to +6.
The hexavalent uranyl ion UO22+ is highly stable and prevalent in natural water systems. Scientists enrich uranium to significantly increase its percentage of the uranium-235 isotope. The leftover depleted byproduct of this enrichment process is extremely dense. Manufacturers utilize depleted uranium for specialized non-nuclear applications like aircraft counterweights and radiation shielding.