- Uranium (U) is a dense, silvery-gray, weakly radioactive metal with atomic number 92, belonging to the actinide series of the periodic table.
- Its electron configuration is [Rn] 5f³ 6d¹ 7s², and it typically forms U⁶⁺ and U⁴⁺ ions in compounds, though U³⁺ and U⁵⁺ oxidation states are also known. The atomic structure contains ninety-two protons, most commonly one hundred and forty-six neutrons in its most abundant isotope, and ninety-two electrons distributed in seven shells.
- Naturally occurring uranium consists primarily of uranium-238 (²³⁸U, 99.2745%), uranium-235 (²³⁵U, 0.7200%), and a trace amount of uranium-234 (²³⁴U, 0.0055%).
- Uranium is relatively common in the Earth’s crust, with an abundance of about 2–4 parts per million—more abundant than silver, tin, or mercury. Major uranium minerals include uraninite (UO₂), pitchblende, carnotite (K₂(UO₂)₂(VO₄)₂·3H₂O), and autunite (Ca(UO₂)₂(PO₄)₂·10-12H₂O). Significant deposits are found in Kazakhstan, Canada, Australia, Namibia, and Russia.
- The element was discovered in 1789 by German chemist Martin Heinrich Klaproth, who isolated it from pitchblende and named it after the newly discovered planet Uranus. Metallic uranium was first prepared in 1841 by French chemist Eugène-Melchior Péligot by reducing uranium tetrachloride with potassium. Uranium’s radioactive properties were revealed in 1896 by French physicist Henri Becquerel, a discovery that paved the way for nuclear physics.
- Uranium is most famous for its role as a nuclear fuel and as the primary material for nuclear weapons. The isotope ²³⁵U is fissile, capable of sustaining a chain reaction when struck by thermal neutrons, making it essential for both nuclear reactors and atomic bombs. The more abundant ²³⁸U is not fissile but is fertile, meaning it can be converted into fissile plutonium-239 (²³⁹Pu) through neutron capture. Uranium-233 (²³³U) can also be bred from thorium-232. In addition to energy production, depleted uranium (mostly ²³⁸U) is used for armor-piercing projectiles, counterweights in aircraft, and radiation shielding.
- Chemically, uranium is reactive, forming a range of oxides (UO₂, U₃O₈, UO₃), halides, and complex uranyl compounds (UO₂²⁺). It oxidizes readily in air to form a thin layer of uranium oxide and reacts slowly with water. The uranyl ion is soluble and mobile in the environment, influencing uranium’s geochemical behavior.
- Biologically, uranium has no known essential function and is both chemically toxic (as a heavy metal) and radiologically hazardous. Ingestion or inhalation can damage the kidneys, lungs, and bones, and long-term exposure increases cancer risk.
- From an environmental standpoint, uranium occurs naturally in soil, water, and rocks, but mining and processing can lead to contamination. Tailings from uranium mines contain radioactive decay products such as radium and radon gas, requiring careful containment. Nuclear waste management for spent uranium fuel remains a major challenge due to the long-lived isotopes involved.
