Protactinium

Atomic properties
Atomic number	91
Standard atomic weight	231.035 88(2)
Electron configuration	[Rn] 5f2 6d1 7s2
Physical properties
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
Electronegativity	1.5 (Pauling)
Ionization energy
	5.89(12) eV; 568(12) kJ mol−1
Atomic radii
Covalent radius	200 pm
Metallic radius	163 pm
Ionic radius	92 pm (Pa5+, Oh)
Thermodynamic properties
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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thorium ← protactinium → uranium

Pr
↑
Pa
↓
—

Protactinium (symbol: Pa) is a member of the actinoid series of chemical elements.

Notes and references

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

↑ ^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>.
↑ ^2.0 ^2.1 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; pp 1450–86. ISBN 0-08-022057-6.
↑ Pauling, Linus The Nature of the Chemical Bond, 3rd ed.; Ithaca, NY, 1960; pp 88–95. ISBN 0-8014-0333-2.
↑ 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.
↑ 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.
↑ 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.

See also the corresponding article on Wikipedia.

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