Chemical element · reference page

92U

Uranium

Uranium is element 92 (U), located in period 7, group — and the f block. At room temperature its reference phase is solid. Its electron configuration is [Rn] 5f3 6d1 7s2.

Atomic number92

Standard atomic weight238.02891(3)

Group—

Period7

Blockf

Electron configuration[Rn] 5f3 6d1 7s2

Electronic structure

What controls its chemistry

Actinide chemistry involves the 5f, 6d and 7s orbitals. The early actinides can access several oxidation states; for the heavier members, +3 becomes increasingly important.

Every actinide is radioactive. Nuclear stability and isotope half-life are therefore inseparable from the chemistry, especially for elements that exist only in trace quantities or must be produced artificially.

Chemical forms

Compounds, ions and materials

Actinides form oxides, halides and coordination compounds, with several oxidation states accessible for the early members. The chemistry cannot be separated from radiochemistry because every isotope is radioactive and sample composition can change through decay.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 19.1 g/cm³. The melting point is 1 407 K (1 134 °C). The boiling point is 4 404 K (4 131 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where uranium is found and used

In practice, uranium is encountered in nuclear energy, glass color and scientific research.

In practice

Examples of real uses

Nuclear energy

Uranium is important in nuclear fuel cycles or in research on nuclear energy systems.

Glass color

Uranium compounds can colour glass by absorbing selected wavelengths of visible light.

Scientific research

Uranium is produced, isolated or measured mainly to test atomic, nuclear and periodic trends rather than for bulk commercial use.

Periodic position

What its neighbours tell us

Uranium is in period 7. In the f-block sequence shown here, it appears between protactinium and neptunium. This sequence allows a direct comparison with the neighbouring f-block elements.

Reference data

Physical and atomic properties

Classificationactinide

Phase at room temperatureSolid

Electron shells2 · 8 · 18 · 32 · 21 · 9 · 2

Density19.1 g/cm³

Melting point1 407 K (1 134 °C)

Boiling point4 404 K (4 131 °C)

Pauling electronegativity1.38

First ionisation energy597.6 kJ/mol

Electron affinity50.94 kJ/mol

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The discovery of uranium is associated with Martin Heinrich Klaproth. Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is 238.02891(3). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Uranium has no stable isotope. Its isotopes are radioactive, and their half-lives and decay modes become important whenever the element is measured, handled or used.

Safety

Handling and exposure

Uranium is radioactive. Work with it requires radiological controls appropriate to the isotope, activity, radiation type and chemical form.