Protactinium (91)

Protactinium has a bright metallic luster which it retains for some time in air. The element is superconductive below 1.4 K. The element is a dangerous toxic material and requires precautions similar to those used when handling plutonium. Protactinium is one of the rarest and most expensive naturally occurring elements. The element is an α-emitter and is a radiological hazard similar to polonium. Protactinium is a highly toxic and radioactive rare earth metal that requires special handling. It is found in pitchblende and ores form Zaire and is one of the rarest and most expensive naturally occurring elements.

•Name: Protactinium
•Symbol: Pa
•Atomic number: 91
•Atomic weight: 231.03588 (2)
•Standard state: solid at 298 K
•CAS Registry ID: 7440-13-3
•Group in periodic table:
•Group name: Actinoid
•Period in periodic table: 7 (actinoid)
•Block in periodic table: f-block
•Color: silvery metallic
•Classification: Metallic

Historical information
Protactinium was discovered by Otto Hahn, Lise Meitner, Frederick Soddy, John Cranston at 1913 in Germany, England. Name originates from the Greek word "protos" meaning "first". Protactinium is found in pitchblende and ores form Zaire and is one of the rarest and most expensive naturally occurring elements. Protactinium was identified by Fajans and Gaehring in 1913 who named the new element brevium ("brief"). The metal itself was not isolated until 1934 when Aristid Grosse developed two methods. One involved reduction of the pentoxide Pa2O5 with a stream of electrons in a vacuum and the second involved heating the iodide PaI5 under vacuum.

Physical properties
•Melting point: 1841 [or 1568 °C (2854 °F)] K
•Boiling point: 4300 [or ca. 4000 °C (7232 °F)] K
•Density of solid: 15370 kg m-3

Orbital properties
•Ground state electron configuration: [Rn].5f2.6d1.7s2
•Shell structure: 2.8.18.32.20.9.2
•Term symbol: 4K11/2