Uranium Hexafluoride (UF₆) — Properties, Uses & Safety

Overview

Uranium hexafluoride (UF6) is a chemical compound with a molar mass of 352.02 g/mol, consisting of one uranium atom bonded to six fluorine atoms in an octahedral molecular geometry. At standard conditions, UF6 is a white to pale yellow crystalline solid, but it has the unusual property of subliming (transitioning directly from solid to gas) at just 56.5 degrees C, making it one of the few uranium compounds that can exist as a gas at relatively low temperatures. This volatility is precisely why UF6 is the compound of choice for uranium enrichment — the process of increasing the concentration of the fissile isotope uranium-235 (U-235) relative to the more abundant uranium-238 (U-238). In gas centrifuge enrichment, gaseous UF6 is spun at extremely high speeds, and the slight mass difference between U-235-F6 and U-238-F6 molecules allows separation. UF6 carries numerous GHS hazard codes: H280 (gas under pressure), H290 (corrosive to metals), H300 (fatal if swallowed), H310 (fatal in contact with skin), H314 (causes severe skin burns), H330 (fatal if inhaled), and H373 (may cause organ damage). It is both chemically toxic (due to uranium's heavy metal toxicity) and radioactive, and it reacts violently with water to produce corrosive hydrofluoric acid (HF) and uranyl fluoride (UO2F2). For chemistry students, uranium hexafluoride connects to several advanced topics: octahedral molecular geometry and VSEPR theory, isotope separation based on mass differences (connecting to Graham's law of effusion), nuclear chemistry and fission, and the intersection of chemistry with geopolitics and energy policy. The Manhattan Project's use of gaseous diffusion to enrich uranium for the first atomic weapons demonstrates how fundamental chemistry principles can have world-changing consequences. UF6 also illustrates sublimation, phase diagrams, and the unique chemistry of actinide elements.

IUPAC Name

uranium(VI) hexafluoride

CAS Number

7783-81-5

PubChem CID

61339

Molecular Formula

UF₆

Molar Mass

352.019 g/mol

State at STP

solid

Appearance

White to pale yellow crystalline solid; sublimes at 56.5 degrees C