Difference between revisions of "Protactinium"

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'''Protactinium''' (symbol: '''Pa''') is a [[chemical element]], a member of the [[actinoid]] series. Although all [[isotope]]s of protactinium are unstable, [[protactinium-231]] (''t''<sub>½</sub>&nbsp;= {{nowrap|3.276(11){{e|4}} a}})<ref name="NUBASE">{{NUBASE2003}}.</ref> is formed as a decay product of [[uranium-235]] (''t''<sub>½</sub>&nbsp;= {{nowrap|704(1){{e|6}} a}}) and so small amounts of protactinium are present in all samples of natural [[uranium]].
 
'''Protactinium''' (symbol: '''Pa''') is a [[chemical element]], a member of the [[actinoid]] series. Although all [[isotope]]s of protactinium are unstable, [[protactinium-231]] (''t''<sub>½</sub>&nbsp;= {{nowrap|3.276(11){{e|4}} a}})<ref name="NUBASE">{{NUBASE2003}}.</ref> is formed as a decay product of [[uranium-235]] (''t''<sub>½</sub>&nbsp;= {{nowrap|704(1){{e|6}} a}}) and so small amounts of protactinium are present in all samples of natural [[uranium]].
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 +
The existence of an element between [[thorium]] and uranium was predicted in 1871 by [[Dmitri Mendeleev|Mendeleev]], who named the putative element eka-tantalum. The chemistry of protactinium resembles that of [[niobium]] and [[tantalum]], with a preponderence of the +5 [[oxidation state]], and [[periodic table]]s from before the Second World War often placed protactinium as a [[transition metal]].
  
 
==Notes and references==
 
==Notes and references==

Revision as of 15:58, 14 April 2011

thorium ← protactinium → uranium
Pr
↑
Pa
↓
—
Atomic properties
Atomic number 91
Standard atomic weight 231.035 88(2)
Electron configuration [Rn] 5f2 6d1 7s2 [note 1]
Physical properties[1][2]
Melting point 1565(19) °C (1838 K)
Boiling point ca. 4227 °C (4500 K)
Density 15.37(8) g cm−3
Electric resistivity 19.1 × 10−6 Ω cm
Chemical properties[3]
Electronegativity 1.5 (Pauling)
Ionization energy[4]
5.89(12) eV
568(12) kJ mol−1
Atomic radii[1][5][6]
Covalent radius 200 pm
Metallic radius 163 pm
Ionic radius 92 pm (Pa5+, Oh)
Thermodynamic properties[2]
Enthalpy change of fusion 16.7 kJ mol−1
Enthalpy change of vaporization 481 kJ mol−1
Miscellaneous
CAS number 7440-13-3
Where appropriate, and unless otherwise stated, data are given for 100 kPa (1 bar) and 298.15 K (25 °C).
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Protactinium (symbol: Pa) is a chemical element, a member of the actinoid series. Although all isotopes of protactinium are unstable, protactinium-231 (t½ = 3.276(11) × 104 a)[7] is formed as a decay product of uranium-235 (t½ = 704(1) × 106 a) and so small amounts of protactinium are present in all samples of natural uranium.

The existence of an element between thorium and uranium was predicted in 1871 by Mendeleev, who named the putative element eka-tantalum. The chemistry of protactinium resembles that of niobium and tantalum, with a preponderence of the +5 oxidation state, and periodic tables from before the Second World War often placed protactinium as a transition metal.

Notes and references

Notes

  1. ↑ The configuration [Rn] 5f1 6d2 7s2 is given as a possible alternative in some textbooks.

References

  1. ↑ 1.0 1.1 Myasoedov, Boris F.; Kirby, H. W.; Tananaev, Ivan G. Protactinium. In The Chemistry of the Actinide and Transactinide Elements, 3rd ed.; Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean, Eds.; Springer: Dordrecht, the Netherlands, 2006; Vol. 1, Chapter 4, pp 161–252. doi:10.1007/1-4020-3598-5_4, <http://radchem.nevada.edu/classes/rdch710/files/protactinium.pdf>.
  2. ↑ 2.0 2.1 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; pp 1450–86. ISBN 0-08-022057-6.
  3. ↑ Pauling, Linus The Nature of the Chemical Bond, 3rd ed.; Ithaca, NY, 1960; pp 88–95. ISBN 0-8014-0333-2.
  4. ↑ Sugar, Jack Ionization energies of the neutral actinides. J. Chem. Phys. 1973, 59, 788–91. DOI: 10.1063/1.1680091. Sugar, Jack Revised ionization energies of the neutral actinides. J. Chem. Phys. 1974, 60, 4103. DOI: 10.1063/1.1680874.
  5. ↑ Cordero, Beatriz; Gómez, Verónica; Platero-Prats, Ana E.; Revés, Marc; Echeverría, Jorge; Cremades, Eduard; Barragán, Flavia; Alvarez, Santiago Covalent radii revisited. Dalton Trans. 2008 (5), 2832–38. DOI: 10.1039/b801115j.
  6. ↑ Shannon, R. D. Revised effective ionic radii and systematic studies of interatomic distances in halids and chalcogenides. Acta Crystallogr. A 1976, 32 (5), 751–67. DOI: 10.1107/S0567739476001551.
  7. ↑ Audi, G.; Bersillon, O.; Blachot, J.; Wapstra, A. H. The NUBASE evaluation of nuclear and decay properties. Nucl. Phys. A 2003, 729, 3–128. doi:10.1016/j.nuclphysa.2003.11.001, <http://amdc.in2p3.fr/nubase/Nubase2003.pdf>.

External links

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