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Uranium (U), element 92
Uranium (U) is the chemical element with atomic number 92: an actinide of period 7, in the row the table hangs outside the group grid. At 25 °C it is a solid, with an atomic mass of 238 u.
Physical and chemical data
| Atomic number | 92 |
|---|---|
| Symbol | U |
| Atomic mass | 238 u |
| Density | 18.95 g/cm³ |
| Melting point | 1,134.85 °C (1,408 K) |
| Boiling point | 4,130.85 °C (4,404 K) |
| Electronegativity (Pauling) | 1.38 |
| Electron configuration | [Rn]7s2 5f3 6d1 |
| Atomic radius (van der Waals) | 240 pm |
| Oxidation states | +6, +5, +4, +3 |
| Physical state at 25 °C | solid |
| Family | actinide |
| Group and period | f-block / 7 |
| Discoverer and year | Martin Heinrich Klaproth (1789) |
The discovery record belongs to Martin Heinrich Klaproth, in 1789.
Neighbours on the table
Horizontally, one proton less lands on Protactinium (Z=91); one more lands on Neptunium (Z=93). Within the actinide series, the closest relatives are Actinium, Thorium, Plutonium, Americium.
The story behind the name
Klaproth named it in 1789 after Uranus, the planet discovered eight years earlier, starting the planetary fashion that would later name neptunium and plutonium. For a century it was merely a yellow green tint for glass and ceramics, until Becquerel noticed in 1896 that uranium salts fogged photographic plates in the dark: radioactivity was discovered by accident in an element already sitting on the shelves. Half a century later the same atom split history into before and after 1945. Its isotope 238 has a half-life the age of the Earth, making it the standard geological clock.
Physical and chemical data: PubChem Periodic Table (NCBI, compiling NIST and IUPAC), public domain, snapshot of 2026-07-10. Temperatures converted from kelvin; historical notes cross checked against classic chemistry references.
Last updated: · Methodology and sources