|Name, Symbol, Number||Protactinium, Pa, 91|
|Chemical series||Transition metals|
|Group, Period, Block||_ [?], 7, f|
|Density, Hardness||15370 kg/m3, no data|
|Appearance||bright, silvery metallic luster|
|Atomic weight||231.03588(2) amu|
|Atomic radius (calc.)||180 (no data) pm|
|Covalent radius||no data|
|van der Waals radius||no data|
|e- 's per energy level||2, 8, 18, 32, 20, 9, 2|
|Oxidation states (Oxide)||5 (weak base)|
|State of matter||solid|
|Melting point||2113 K (2912 °F)|
|Boiling point||4300 K (7281 °F)|
|Molar volume||15.18 ×10-3 m3/mol|
|Heat of vaporization||470 kJ/mol|
|Heat of fusion||15 kJ/mol|
|Vapor pressure||5.1E-5 Pa at 2200 K|
|Velocity of sound||no data|
|Electronegativity||1.5 (Pauling scale)|
|Specific heat capacity||120 J/(kg*K)|
|Electrical conductivity||5.29 106/m ohm|
|Thermal conductivity||47 W/(m*K)|
|1st ionization potential||568 kJ/mol|
|2nd ionization potential||no data|
|3rd ionization potential||no data|
|4th ionization potential||no data|
|Most Stable Isotopes|
|SI units & STP are used except where noted.|
Protactinium is a silver metallic element that belongs to the actinide group, with a bright metallic luster that it retains for some time in the air. It is superconductive at temperatures below 1.4 K.
Due to its scarcity, high radioactivity and toxicity, there are currently no uses for protactinium outside of basic scientific research.
Protactinium was first identified in 1913, when Kasimir Fajans[?] and O. H. Göhring[?] encountered short-lived isotope 234m-Pa, with a half-life of about 1.17 minutes, during their studies of the decay chain of 238-U. They gave the new element the name Brevium (lat. brevis, brief, short); the name was changed to Protoactinium in 1918 when two groups of scientists (Otto Hahn and Lise Meitner of Germany and Frederick Soddy and John Cranston[?] of Great Britain) independently discovered 231-Pa, and shortened to Protactinium in 1949.
Aristid V. Grosse[?] prepared 2 mg of Pa2O5 in 1927, and later on managed to isolate Protactinium for the first time in 1934 from 0.1 mg of Pa2O5, first converting the oxide to a iodide and then cracking it in a high vacuum by an electrically heated filament by the reaction 2PaI5 → 2Pa + 5I2.
In 1961, the Great Britain Atomic Energy Authority was able to produce 125 g of 99.9% pure Protactinium, processing 60 tons of waste material in a 12-stage process and spending 500,000 USD; this was the world's only supply of the element for many years to come, and it is reported that the metal was sold to laboratories for a cost of 2,800 USD / g in the following years.
Protactinium does not play any biological role.
Known Protactinium compounds include:
29 radioisotopes of Protactinium have been characterized, with the most stable being 231-Pa with a half life of 32760 years, 233-Pa with a half-life of 26.967 days, and 230-Pa with a half-life of 17.4 days. All of the remaining radioactive isotopes have half-lifes that are less than 1.6 days, and the majority of these have half lifes that are less than 1.8 seconds. This element also has 2 meta states, 217m-Pa (t½ 1.15 milliseconds) and 234m-Pa (t½ 1.7 minutes).
The primary decay mode before the most stable isotope, 231-Pa, is Alpha decay and the primary mode after is Beta minus decay. The primary decay products before 231-Pa are element Ac (Actinium) isotopes and the primary products after are element U (Uranium) isotopes.
Protactinium is both toxical and highly radioactive; it requires precautions similar to those used when handling plutonium.