Protactinium
Element 91 · Actinide
Protactinium is one of the rarest and most expensive naturally occurring elements. It is a dense, silvery metal that is highly radioactive and toxic. In its most stable oxidation state, +5, it resembles niobium and tantalum chemically. Because it is so scarce and hazardous, protactinium has been studied mainly to understand actinide chemistry; it has no significant commercial applications.
Key facts
| Atomic number | 91 |
|---|---|
| Atomic weight | 231.04 |
| Category | Actinide |
| Group / Period | — / 7 |
| Block | f |
| Electron configuration | [Rn] 5f2 6d1 7s2 |
| Common oxidation states | +5, +4 |
| State at STP | Solid |
| Electronegativity | 1.5 |
| Density | 15.37 g/cm3 |
| Melting point | 1562 °C |
| Boiling point | 4027 °C (estimated) |
Occurrence
Protactinium-231 occurs in uranium ores at roughly one part per ten million parts of uranium, formed by decay of uranium-235. Only tiny amounts have ever been isolated.
Applications
Research into actinide chemistry and separation science
Tracer studies of uranium-series decay chains
No commercial applications
Common compounds
- Protactinium(V) oxide (Pa2O5)
- Protactinium(V) fluoride (PaF5)
- Protactinium(IV) oxide (PaO2)
Protactinium was identified in 1913 and isolated in 1918 by Otto Hahn and Lise Meitner; its name means 'parent of actinium' because it decays into actinium.
Data source: IUPAC standard atomic weights 2021