Uranium (U)
Element 92 · Actinide · atomic mass 238.03 u · f-block, period 7
Electron shells: 2, 8, 18, 32, 21, 9, 2
Uranium is the heaviest element found in significant quantity in nature and the fuel of both nuclear power and weapons. Its slow decay is a major source of the Earth's internal heat.
Uranium was used to colour glass a fluorescent yellow-green a century before anyone knew about fission.
- Atomic number
- 92
- Atomic mass
- 238.03 u
- Electron configuration
- [Rn] 7s² 5f³ 6d¹
- Group · period · block
- f-block · 7 · f
- Oxidation states
- +3, +4, +5, +6
- Electronegativity
- 1.38 (Pauling)
- Melting point
- 1,135 °C
- Boiling point
- 4,131 °C
- Density
- 18.95 g/cm³
- State at 20 °C
- Solid
- Appearance
- Silvery-grey metal
- Discovered
- Martin Heinrich Klaproth, 1789
92 protons, and 92 electrons when neutral
IUPAC standard atomic weight
Shown in the strip below the table
What Uranium is used for
- Nuclear reactor fuel
- Radiometric dating of rocks
- Depleted uranium ballast and armour
- Historically, yellow-green glass and glazes
Atomic structure of Uranium
A neutral uranium atom has 92 protons and 92 electrons. Its most common isotope carries about 146 neutrons, which is where the mass number 238 comes from. Change the neutron count and you have a different isotope of uranium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 32, 21, 9, 2. In orbital notation that is [Rn] 7s² 5f³ 6d¹. As a f-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Uranium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Uranium sits in the periodic table
The second f-block row, elements 89-103. All are radioactive, and everything past uranium is essentially man-made.
- One proton lighter: Protactinium.
- One proton heavier: Neptunium.
Discovery and naming
Uranium was discovered by Martin Heinrich Klaproth in 1789. Its name comes from The planet Uranus.
Every isotope of uranium is radioactive, so it has no standard atomic weight. Periodic tables show the mass number of its longest-lived isotope in square brackets instead.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Uranium?
The standard atomic weight of Uranium is 238.03 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Uranium have?
Uranium has 92 protons, because the atomic number is the proton count and that is what makes an atom Uranium at all. A neutral Uranium atom has the same number of electrons, 92. The neutron count varies by isotope; the most common one has about 146, since 238 − 92 = 146.
What is the electron configuration of Uranium?
The electron configuration of Uranium is [Rn] 7s² 5f³ 6d¹. Its electrons are arranged 2, 8, 18, 32, 21, 9, 2 across 7 shells.
Is Uranium a metal?
Yes. Uranium is classified as a actinide, on the metallic side of the table.
What group and period is Uranium in?
Uranium sits in the f-block strip below the main table, in period 7, among the actinides. Elements in that strip are not given a group number in the standard 18-column layout.
What is the charge of Uranium?
Uranium most commonly forms a 6+ or 4+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound. Across all its compounds it shows oxidation states of +3, +4, +5, +6.
What is the melting point of Uranium?
Uranium melts at 1,135 °C and boils at 4,131 °C. That puts it in the solids at everyday temperatures.
What is Uranium used for?
Nuclear reactor fuel, Radiometric dating of rocks, Depleted uranium ballast and armour, Historically, yellow-green glass and glazes. Uranium is the heaviest element found in significant quantity in nature and the fuel of both nuclear power and weapons.
Who discovered Uranium, and where does its name come from?
Uranium (U) was discovered by Martin Heinrich Klaproth in 1789. The name comes from The planet Uranus.
Is Uranium radioactive?
Yes. Every isotope of Uranium is radioactive — it has no stable form at all, which is why the periodic table shows its mass in square brackets rather than as a standard atomic weight.