Protactinium
actinideProperties
| Property | Value |
|---|---|
| Atomic Mass | 231.04 amu |
| Category | actinide |
| Period | 7 |
| Electron Configuration | [Rn] 5f2 6d1 7s2 |
| Electronegativity | 1.5 (Pauling) |
| Oxidation States | 5, 4 |
| Melting Point | 1841 K (1567.8 °C) |
| Boiling Point | 4300 K (4026.8 °C) |
| Density | 15.37 g/cm³ |
| Discovered By | Kasimir Fajans, Oswald Helmuth Gohring (1913) |
About Protactinium
Protactinium gets its name from being the 'parent of actinium' — ²³¹Pa alpha-decays to ²²⁷Ac with a 32,760-year half-life. Fajans and Göhring spotted the short-lived ²³⁴ᵐPa in 1913 in a uranium decay chain, but the long-lived parent had to wait until 1917, when Hahn and Meitner in Berlin and Soddy and Cranston in Glasgow independently isolated milligram quantities. The chemistry is genuinely awful to do: Pa(V) hydrolyzes at almost any pH and adsorbs onto glass walls, silica, even Teflon, so working solutions need fluoride or oxalate complexants just to keep the metal in solution. The 1961 Atomic Energy Authority isolation of 125 grams from 60 tonnes of uranium-ore residue is still the largest stockpile ever produced and cost about $500,000 in 1961 dollars. The Pa(IV) state appears under reducing conditions and is one of the few places where the 5f² configuration matters for actinide spectroscopy.
Fun Fact
Pa(V) hydrolyzes and adsorbs onto almost any surface — glass, silica, even Teflon — at trace concentrations, so working solutions need fluoride or oxalate complexants just to stay in solution long enough to pipette.
Common Uses
- ²³¹Pa/²³⁰Th sediment dating for ocean circulation reconstruction over 100,000 year scales
- Reference material for actinide solution chemistry studies
- Probe for 5f-orbital bonding in early actinides
- Tracer in uranium-series geochronology of corals and speleothems
- Target material for synthesizing heavier transuranics by neutron capture
- Calibration standard for alpha spectrometry detectors