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, of interest mainly for scientific research. Currently it has no practical applications, but some researchers have noted that it could be used in making nuclear weapons.

Contents

1 Occurrence
2 History
3 Notable Characteristics

3.1 Isotopes


4 Compounds
5 Applications
6 Precautions
7 See also
8 Notes
9 References
10 External links
11 Credits



Occurrence
The isotope protactinium-231 occurs in pitchblende to the extent of about one part per ten 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 three parts per million (ppm).

History
The existence of an element between thorium and uranium was predicted by Dmitri Mendeleev in 1871. In 1900, William Crookes isolated protactinium as a radioactive material from uranium, but he could not identify the material.[1]
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 two milligrams (mg) of the oxide Pa2O5 in 1927. About seven years later, he managed to isolate protactinium for the first time from 0.1 milligrams (mg) of Pa2O5, by 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 U.K. Atomic Energy Authority produced 125 grams (g) of 99.9 percent 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 of the actinide series, situated in period seven 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 (t½) 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 two meta states, 217m-Pa (t½ 1.15 milliseconds) and 234m-Pa (t½ 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 practical uses for protactinium, and it is mainly used for basic scientific research.
Some researchers have observed that 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 with protactinium-231.

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

See also
Chemical element
Inner transition metal
Metal
Periodic table
Radioactive decay
Notes

↑ John Emsley, Nature's Building Blocks (Oxford: Oxford Univ. Press, 2001), 347. ISBN 0198503407


ReferencesISBN links support NWE through referral fees
Emsley, John. 2001. Nature's Building Blocks: An A–Z Guide to the Elements. Oxford: Oxford Univ. Press. ISBN 0198503407
Greenwood, N.N., and A. Earnshaw. 1998. Chemistry of the Elements, 2nd ed. Oxford, UK; Burlington, MA: Butterworth-Heinemann. ISBN 0750633654
Hampel, Clifford A. 1968. The Encyclopedia of the Chemical Elements. New York: Reinhold Book Corp. ISBN 0442155980
Morss, Lester R., Norman M. Edelstein, and Jean Fuger, eds. 2006. The Chemistry of the Actinide and Transactinide Elements. 3rd ed. 5 vols. Joseph J. Katz, adapter. Dordrecht: Springer. ISBN 1402035551
Stwertka, Albert. 1998. Guide to the Elements. Rev. ed. Oxford: Oxford University Press. ISBN 0-19-508083-1
External links
All links retrieved December 2, 2022.

Protactinium The University of Sheffield and WebElements Ltd.
Thomas Jefferson National Accelerator Facility, Office of Science Education. It's Elemental: Protactinium Jefferson Lab.
Chemical & Engineering News. Protactinium American Chemical Society.

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