Protactinium

91 thorium ← protactinium → uranium Pr ↑ Pa ↓ (Uqu) periodic table
General
Name, Symbol, Number	protactinium, Pa, 91
Chemical series	actinides
Group, Period, Block	n/a, 7, f
Appearance	bright, silvery metallic luster
Atomic mass	231.03588(2) g/mol
Electron configuration	[Rn] 5f2 6d1 7s2
Electrons per shell	2, 8, 18, 32, 20, 9, 2
Physical properties
Phase	solid
Density (near r.t.)	15.37 g/cm³
Melting point	1841 K (1568 °C, 2854 °F)
Boiling point	? 4300 K (? 4027 °C, ? °F)
Heat of fusion	12.34 kJ/mol
Heat of vaporization	481 kJ/mol
Atomic properties
Crystal structure	orthorhombic
Oxidation states	2, 3, 4, 5 (weakly basic oxide)
Electronegativity	1.5 (Pauling scale)
Ionization energies	1st: 568 kJ/mol
Atomic radius	180 pm
Miscellaneous
Magnetic ordering	no data
Electrical resistivity	(0 °C) 177 nΩ·m
Thermal conductivity	(300 K) 47 W/(m·K)
CAS registry number	7440-13-3
Notable isotopes
Main article: Isotopes of protactinium iso NA half-life DM DE (MeV) DP 230Pa syn 17.4 d ε 1.310 230Th β- 0.563 230U 231Pa syn 32760 y α 5.149 227Ac 233Pa syn 26.967 d β- 0.571 233U

Protactinium (chemical symbol Pa, atomic number 91) is a member of the actinide series of chemical elements. It is a toxic, highly radioactive material, which is of interest mainly for scientific research. Currently it has no practical applications, although some have suggested its use in making nuclear weapons.

Occurrence

The isotope protactinium-231 occurs in pitchblende to the extent of about 1 part per 10 million parts of ore. Some ores from the Democratic Republic of the Congo have been found to contain the element at a concentration of about 3 parts per million (ppm).

History

The existence of an element between thorium and uranium was predicted to exist by Dmitri Mendeleev in 1871. In 1900, William Crookes isolated protactinium as a radioactive material from uranium, but he could not identify the material.

Protactinium was first identified in 1913, when Kasimir Fajans and O. H. Göhring encountered short-lived isotope protactinium-234m, with a half-life of about 1.17 minutes, during their studies of the decay chain of uranium-238. They gave the new element the name brevium (Latin brevis, meaning brief or 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 the UK) independently discovered Pa-231. The name was shortened to protactinium in 1949.

Aristid V. Grosse prepared 2 milligrams (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 an iodide and then cracking it in a high vacuum by an electrically heated filament by the reaction 2PaI₅ → 2Pa + 5I₂.

In 1961, the United Kingdom Atomic Energy Authority was able to produce 125 g of 99.9% pure protactinium, after 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 has been reported that the metal was sold to laboratories at a price of 2,800 USD per gram.

Notable Characteristics

Protactinium is an inner transition metal (or actinide) that lies in period 7 of the periodic table, between thorium and uranium. It retains a bright silvery luster for some time in the air. It is superconductive at temperatures below 1.4 K.

Isotopes

Many radioisotopes of protactinium have been characterized. The most stable of these are 231-Pa, with a half-life of 32,760 years; 233-Pa, with a half-life of 26.967 days; and 230-Pa, with a half-life of 17.4 days. All the remaining radioactive isotopes have half-lives that are less than 1.6 days, and the majority of these have half-lives that are less than 1.8 seconds. This element also has 2 meta states, 217m-Pa (t_½ 1.15 milliseconds) and 234m-Pa (t_½ 1.17 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 actinium isotopes, and the primary products after are uranium isotopes.

Compounds

Known compounds of protactinium include the following:

• Fluorides:
  • protactinium(IV) fluoride (PaF₄)
  • protactinium(V) fluoride (PaF₅)
• Chlorides:
  • protactinium(IV) chloride (PaCl₄)
  • protactinium(V) chloride (PaCl₅)
• Bromides:
  • protactinium(IV) bromide (PaBr₄)
  • protactinium(V) bromide (PaBr₅)
• Iodides:
  • protactinium(III) iodide (PaI₃)
  • protactinium(IV) iodide (PaI₄)
  • protactinium(V) iodide (PaI₅)
• Oxides:
  • protactinium(II) oxide (PaO)
  • protactinium(IV) oxide (PaO₂)
  • protactinium(V) oxide (Pa₂O₅)

Applications

Given its scarcity, high radioactivity, and toxicity, there are currently no uses for protactinium outside of basic scientific research.

Protactinium-231, which is formed by the alpha decay of uranium-235, could possibly sustain a nuclear chain reaction and might, in principle, be used to build a nuclear weapon. The critical mass, according to Walter Seifritz, is 750±180 kilograms (kg). Other authors conclude that no chain reactions are possible in protactinium-231.

Precautions

Protactinium is both toxic and highly radioactive. It requires precautions similar to those used when handling plutonium.

References

ISBN links support NWE through referral fees

• "Protactinium" Los Alamos National Laboratory, Chemistry Division. Retrieved March 10, 2007.

• Chang, Raymond. 2006. Chemistry. 9th ed. New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031.

• Greenwood, N.N., and A. Earnshaw. 1998. Chemistry of the Elements 2nd ed. Oxford, UK; Burlington, MA: Butterworth-Heinemann. ISBN 0750633654. Online version.

• Cotton, F. Albert, and Geoffrey Wilkinson. 1980. Advanced Inorganic Chemistry. 4th ed. New York: Wiley. ISBN 0-471-02775-8.

• "Protactinium" WebElements.com. Retrieved March 10, 2007.

External links

• Protactinium WebElements.com.
• Protactinium It's Elemental.
• [1] InfoHaunter

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