Uranium

Uranium is the heaviest naturally occurring element and the fuel of the nuclear age. Discovered in 1789, it was just a chemical curiosity for 150 years until the discovery of nuclear fission in 1938 transformed it into the most politically significant element in history: the foundation of nuclear power and nuclear weapons.

• Atomic Number9292 protons, 92 electrons
• Atomic Mass238.0289 u92× heavier than hydrogen
• State at Room TempSolidSolid
• Density18.95 g/cm³
• Melting / Boiling1134.8°C / 4130.9°C
• Discovered1789

What is Uranium?

Uranium is an actinide with 92 protons. Uranium-238 (half-life 4.5 billion years) and uranium-235 (half-life 700 million years) both occur naturally. Uranium-235 is fissile, it can sustain a nuclear chain reaction when bombarded with neutrons. Enriching natural uranium to increase U-235 content from 0.7% to 3-5% produces reactor fuel; enriching to 90%+ produces weapons-grade material. Discovered by Martin Klaproth in 1789, named after the planet Uranus.

Fact Uranium is element 92, symbol U. As an actinide, it is part of the f-block of the periodic table: one of 15 radioactive elements from actinium (89) to lawrencium (103). All actinides are radioactive; none has a stable isotope. They are produced in nuclear reactors and by decay of heavier elements, and their chemistry has been studied using only microgram or nanogram quantities.

Where you find Uranium

On Earth

Uranium does not occur in significant natural abundance. It is found in trace quantities in uranium ores as a product of neutron capture and radioactive decay. World production is measured in micrograms or milligrams per year.

How we use Uranium

Uranium is an actinide with 92 protons

How it was discovered

Uranium is an actinide with 92 protons. Uranium-238 (half-life 4.5 billion years) and uranium-235 (half-life 700 million years) both occur naturally. Uranium-235 is fissile, it can sustain a nuclear chain reaction when bombarded with neutrons. Enriching natural uranium to increase U-235 content from 0.7% to 3-5% produces reactor fuel; enriching to 90%+ produces weapons-grade material. Discovered by Martin Klaproth in 1789, named after the planet Uranus.

Deeper dive: uranium and the actinide series

The actinides (elements 89-103) form the lower of the two rows below the main body of the periodic table. They represent the filling of the 5f electron subshell. Unlike the lanthanides (the upper row), the actinides show greater variety in their chemistry because the 5f, 6d and 7s orbitals are close in energy. The early actinides, thorium through neptunium, can show many different oxidation states (e.g. uranium from +3 to +6). The heavier actinides increasingly resemble the lanthanides in preferring the +3 state.

All actinides beyond bismuth (83) are radioactive. The lightest, thorium, protactinium and uranium, have long enough half-lives to survive from the formation of the solar system. Neptunium and beyond are almost entirely synthetic, produced in nuclear reactors or accelerators. The transuranic elements were created at remarkable facilities including Oak Ridge National Laboratory, the Berkeley Cyclotron, the GSI in Darmstadt and JINR in Dubna.

Moving to 93 protons brings us to the next element on the periodic table.