Protactinium

properties
[ Rn ] 5 f 2 6 d 1 7 s 2 91 Pa Periodic table
General
Name , symbol , atomic number	Protactinium, Pa, 91
Element category	Actinoids
Group , period , block	Ac , 7 , f
Appearance	bright, silvery, shiny metallic
CAS number	7440-13-3
EC number	616-087-9
ECHA InfoCard	100.122.906
Mass fraction of the earth's envelope	9 · 10 −8  ppm
Atomic
Atomic mass	231.03588 (2) et al
Atomic radius	180 pm
Covalent radius	200 pm
Electron configuration	[ Rn ] 5 f 2 6 d 1 7 s 2
1. Ionization energy	5.89 (12) eV ≈ 568 kJ / mol
2. Ionization energy	11.9 (4) eV ≈ 1 150 kJ / mol
3. Ionization energy	18th.6 (4) eV ≈ 1 790 kJ / mol
4. Ionization energy	30th.9 (4) eV ≈ 2 980 kJ / mol
5. Ionization energy	44.3 (4) eV ≈ 4 270 kJ / mol
Physically
Physical state	firmly
Crystal structure	tetragonal
density	15.37 g / cm 3
Melting point	1841 K (1568 ° C)
Molar volume	15.18 10 −6 m 3 mol −1
Heat of evaporation	470 kJ / mol
Heat of fusion	15 kJ mol −1
Electric conductivity	5.56 · 10 6 A · V −1 · m −1
Thermal conductivity	47 W m −1 K −1
Chemically
Oxidation states	5
Electronegativity	1.5 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP 229 Pa {syn.} 1.50 d ε 0.316 229 Th α 5,841 225 Ac 230 Pa {syn.} 17.4 d ε 1,310 230 th β - 0.563 230 U α 5.439 226 Ac 231 Pa 100% 32,760 a α 5.149 227 Ac 232 Pa {syn.} 1.31 d β - 1.337 232 U ε 0.495 232 Th 233 Pa {syn.} 26,967 d β - 0.571 233 U 234 Pa in traces 6.70 h β - 2.197 234 U 234 m Pa in traces 1.17 min β - 2.271 234 U IT 0.074 234 Pa
For other isotopes see list of isotopes
Hazard and safety information
Radioactive
GHS hazard labeling no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Protactinium (originally shortened from Proto-actinium (Greek πρώτος (prõtos) = first and actinium); hyphenation Pro | tac | ti | ni | um or Pro | t | ac | ti | ni | um) is a chemical element with the element symbol Pa and the atomic number 91. In the periodic table it is in the group of actinides ( 7th period , f-block ). It is silvery metallic and becomes superconducting below 1.4 K. It is radioactive and occurs extremely rarely in nature. The greatest amount of protactinium is produced artificially.

history

In 1871, Dmitri Mendeleev postulated the existence of an element between thorium and uranium . The series of actinide elements was still unknown at the time. Therefore, uranium was placed below the tungsten , and thorium below the eka - zirconium (the also undiscovered element hafnium at that time ), whereby the space below the tantalum remained free. The periodic table was represented in this form until the 1950s. For a long time chemists looked for eka-tantalum with similar chemical properties to tantalum.

Mendeleev's periodic table from 1871 with a gap for protactinium at the bottom, between thorium ( Th = 231 ) and uranium ( U = 240 )

In 1900, William Crookes isolated a highly radioactive material from uranium; however, he could not characterize it as a new chemical element and named it Uranium-X (UX). Crookes dissolved uranyl nitrate in ether , the remaining aqueous phase mostly contained the nuclides ²³⁴ Th and ²³⁴ Pa.

^{234 m} Pa was discovered in 1913 by Kasimir Fajans and Oswald Helmuth Göhring , who gave it the name Brevium ( Latin brevis 'short') because of its short half-life (1.17 minutes ).

The long-lived ²³¹ Pa (t _½ = 32,760 years) was found in 1917 by Otto Hahn and Lise Meitner (published in 1918), they called it Protoactinium (from Greek πρῶτος = protos : the first , the preceding , the chemical element that is in the decay series of uranium -235 before the actinium is). Independently, the long-lived isotope was discovered in England by Frederick Soddy and John Arnold Cranston , although the latter could not publish it because he was a soldier in the First World War in 1915.

In 1921 Otto Hahn made the further discovery that there is a second beta-emitting isotope with the same mass number 234 for the brevium 234 found by Fajans, which differs from the brevium only in its longer half-life of 6.7 hours; this is the rare case of nuclear isomerism .

Protactinium was first isolated in 1934 by Aristid von Grosse .

The official name for all three isotopes as well as all artificially produced isotopes with the atomic number 91 was determined by the IUPAC to Protactinium in 1949 , instead of the more difficult to pronounce Protoactinium by Hahn and Meitner.

Occurrence

Protactinium is a radioactive decay product of uranium and is found in nature in the form of the two isotopes ²³¹ Pa and ²³⁴ Pa, whereby the isotope ²³⁴ Pa can occur in two different energy states. Protactinium ²³¹ Pa, an alpha emitter, is created when ²³⁵ U decays (see uranium actinium series ), the beta-emitting protactinium ²³⁴ Pa when uranium ²³⁸ U decays (see uranium radium series ).

Extraction and presentation

In 1927, Aristid von Grosse isolated 2 milligrams of protactinium (V) oxide  (Pa ₂ O ₅ ) from waste from the production of radium . In 1934 he isolated elemental protactinium for the first time from 0.1 milligrams Pa ₂ O ₅ . To do this, he used two different methods: On the one hand, protactinium oxide was irradiated with 35 keV electrons in a vacuum. On the other hand, the oxide was converted to halides ( chloride , bromide or iodide ) and these were then reduced in a vacuum on an electrically heated wire.

Later he also made metallic protactinium from protactinium (V) iodide  (PaI ₅ ).

${\displaystyle {\ce {2 PaI5 -> 2 Pa + 5 I2}}}$

In 1959 and 1961, the United Kingdom Atomic Energy Authority (UKAEA) extracted 125 g of protactinium with a purity of 99.9% from 60 t of spent nuclear fuel in a 12-stage process; the cost was about US $ 500,000. For many years this was the only source of Protactinium available worldwide, from which various laboratories were supplied for scientific research.

properties

In the periodic table , protactinium with atomic number 91 is in the series of actinides , its predecessor is thorium , the next element is uranium . Its analogue in the lanthanide series is praseodymium .

Physical Properties

Protactinium is silvery metallic and becomes superconducting below 1.4 K.

Chemical properties

Protactinium occurs mainly in two oxidation states , +4 and +5, both in solids and in solution.

use

Because of its rarity, high level of radioactivity and toxicity, Protactinium has no practical application other than research.

In protactinium ²³¹ Pa, which is formed when uranium ²³⁵ U decays and is also formed in nuclear reactors through the reaction ²³² Th + n →  ²³¹ Th + 2n and subsequent beta decay , a nuclear chain reaction can possibly take place, which in principle also leads to the construction of nuclear weapons could be used. The critical mass is as specified by Walter Seifritz 750 ± 180 kg. Other authors come to the conclusion that a chain reaction is not possible even with any large mass in Protactinium ²³¹ Pa.

Protactinium ²³³ Pa is an intermediate product in the breeding process from thorium ²³² Th to uranium ²³³ U in thorium high-temperature reactors .

${\displaystyle \mathrm {^{232}_{\ 90}Th\ +\ _{0}^{1}n\ \longrightarrow \ _{\ 90}^{233}Th\ {\xrightarrow[{22,3\ min}]{\beta ^{-}}}\ _{\ 91}^{233}Pa\ {\xrightarrow[{26,967\ d}]{\beta ^{-}}}\ _{\ 92}^{233}U} }$

The times given are half-lives .

Since the availability of modern, very sensitive mass spectrometers , it has become possible to use the ²³¹ Pa as a tracer in paleoceanography, for example .

links

→ Category: Protactinium compound

Protactinium (IV) oxide (PaO ₂ ) is a black, crystalline powder. Protactinium (V) oxide (Pa ₂ O ₅ ) is a white, crystalline powder. Both have a cubic crystal system.

Protactinium (V) chloride (PaCl ₅ ) forms yellow monoclinic crystals and has a chain structure consisting of 7-fold coordinated pentagonal bipyramids.

safety instructions

Classifications according to the GHS regulation are not available because they only include chemical hazards which play a completely subordinate role compared to the hazards based on radioactivity . The latter also only applies if the amount of substance involved is relevant.

literature

• Harold W. Kirby: The Radiochemistry of Protactinium. National Academies, 1959 (PDF)
• Boris F. Myasoedov, Harold W. Kirby, Ivan G. Tananaev: Protactinium. In: Lester R. Morss, Norman M. Edelstein, Jean Fuger (Eds.): The Chemistry of the Actinide and Transactinide Elements. Springer, Dordrecht 2006, ISBN 1-4020-3555-1 , pp. 161-252 ( doi: 10.1007 / 1-4020-3598-5_4 ).
• Eric Scerri : A tale of seven elements , Oxford University Press, Oxford, 2013

Web links

Wiktionary: Protactinium  - explanations of meanings, word origins, synonyms, translations

Commons : Protactinium  - collection of images, videos and audio files

• Entry to Protactinium. In: Römpp Online . Georg Thieme Verlag, accessed on January 3, 2015.
• Linda Raber: Protactinium , Chemical & Engineering News, 2003

Individual evidence

1. ^ Harry H. Binder: Lexicon of the chemical elements. S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 .
2. ↑ The values ​​for the properties (info box) are taken from www.webelements.com (Protactinium) , unless otherwise stated .
3. ↑ CIAAW, Standard Atomic Weights Revised 2013 .
4. ↑ ^{a b c d e} Entry on protactinium in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( https://physics.nist.gov/asd ). Retrieved June 13, 2020.
5. ↑ ^{a b c d e} entry on protactinium at WebElements, https://www.webelements.com , accessed on June 13, 2020.
6. ↑ The hazards emanating from radioactivity do not belong to the properties to be classified according to the GHS labeling. With regard to other hazards, this element has either not yet been classified or a reliable and citable source has not yet been found.
7. ^ Siegfried Niese : The discovery of the element 91 by Kasimir Fajans and Oswald Göhring in 1913 and the naming by Otto Hahn and Lise Meitner in 1918 (digitized version) .
8. ^ ^{A b} John Emsley: Nature's Building Blocks: An AZ Guide to the Elements. Oxford University Press, Oxford, England, UK 2001, ISBN 0-19-850340-7 , pp. 347-349, chapter: Protactinium ( limited preview in Google book search).
9. ↑ Michael Laing: A Revised Periodic Table: With the Lanthanides Repositioned. In: Foundations of Chemistry . 2005, 7 (3), p. 203 ( doi: 10.1007 / s10698-004-5959-9 ).
10. ^ William Crookes: Radio-Activity of Uranium. In: Proceedings of the Royal Society of London . 1899, 66, pp. 409-423 ( doi: 10.1098 / rspl.1899.0120 ).
11. ^ A Glossary of Terms in Nuclear Science and Technology. P. 180 ( limited preview in Google Book search).
12. ^ Sven Johansson: Decay of UX ₁ , UX ₂ , and UZ. In: Physical Review . 1954, 96 (4), p. 1075 ( doi: 10.1103 / PhysRev.96.1075 ; bibcode : 1954PhRv ... 96.1075J ).
13. ↑ K. Fajans: The position of the radio elements in the periodic system. In: Physikalische Zeitschrift . 1913, 14 (4), pp. 136-142.
14. ^ Kasimir Fajans: Radioactive Transformations and the Periodic System of The Elements. In: Reports of the German Chemical Society . 1913, 46, pp. 422-439.
15. ↑ K. Fajans, O. Göhring: About the complex nature of the UrX. In: The natural sciences . 1913, 1 (14), p. 339. (digi-journals) ; doi: 10.1007 / BF01495360 ; bibcode : 1913NW ...... 1..339F .
16. ↑ K. Fajans, O. Göhring: About the uranium X ₂ - the new element of the uranium series. In: Physikalische Zeitschrift . 1913, 14, pp. 877-884.
17. ↑ Otto Hahn, Lise Meitner: The mother substance of actinium, a new radioactive element of long life. In: Physikalische Zeitschrift . 1918, 19, pp. 208-218 ( doi : 10.1002 / bbpc.19180241107 (currently unavailable) ).
18. ↑ Lise Meitner, Otto Hahn: About the Protactinium and the question of the possibility of its production as a chemical element. In: The natural sciences . 1919, 7 (33), pp. 611-612 ( doi: 10.1007 / BF01498184 ).
19. ^ Protactinium, Jefferson Lab
20. ^ John Albert Cranston, University of Glasgow
21. ↑ Cranston, Soddy, The parent of Actinium, Nature, Volume 100, 1918, pp. 498-499
22. ↑ Otto Hahn: About a new radioactive substance in uranium. In: Reports of the German Chemical Society . 1921, 54 (6), pp. 1131-1142 ( doi: 10.1002 / cber.19210540602 ).
23. ↑ Aristid von Grosse: Das Element 91; its properties and its extraction. In: Reports of the German Chemical Society . 1928, 61 (1), pp. 233-245 ( doi: 10.1002 / cber.19280610137 ).
24. ↑ AV Grosse, MS Agruss: The Isolation of 0.1 gram of the Oxide of Element 91 (Protactinium). In: Journal of the American Chemical Society . 1934, 56 (10), p. 2200 ( doi: 10.1021 / ja01325a507 ).
25. ↑ G. Graue, H. Käding: The technical extraction of Protactinium. In: Angewandte Chemie . 1934, 47 (37), pp. 650-653 ( doi: 10.1002 / anie.19340473706 ).
26. ^ AV Grosse: Metallic Element 91. In: Journal of the American Chemical Society . 1934, 56 (10), pp. 2200-2201 ( doi: 10.1021 / ja01325a508 ).
27. ^ Aristid von Grosse: Element 91. In: Science . 1934, 80 (2084), pp. 512-516 ( doi: 10.1126 / science.80.2084.512 , PMID 17734249 ).
28. ↑ Aristid V. Grosse: For the production of Protactinium. In: Reports of the German Chemical Society . 1935, 68 (2), pp. 307-309 ( doi: 10.1002 / cber.19350680218 ).
29. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, The Elements "Protactinium", pp. 4-28-4-29.
30. ^ RD Fowler, BT Matthias, LB Asprey, HH Hill, JDG Lindsay, CE Olsen, RW White: Superconductivity of Protactinium. In: Phys. Rev. Lett. 1965, 15 (22), pp. 860-862 ( doi: 10.1103 / PhysRevLett.15.860 ; bibcode : 1965PhRvL..15..860F ).
31. ↑ Walter Seifritz: Nuclear explosive devices - threat or energy supply for mankind. Thiemig-Verlag, 1984, ISBN 3-521-06143-4 .
32. ↑ S. Ganesan, Umasankari Kannan, PD Krishnani, V. Jagannathan, RP Jain, R. Karthikeyan: A Re-calculation of Criticality Property of ²³¹ Pa Using New Nuclear Data. In: Current Science . 1999, 77 (5), pp. 667-671. (PDF) .
33. ↑ JF McManus, R. Francois, J.-M. Gherardi, LD Keigwin, S. Brown-Leger: Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate changes. In: Nature . 2004, 428, pp. 834-837 ( doi: 10.1038 / nature02494 ; PDF ).
34. ^ RP Dodge, GS Smith, Q. Johnson, RE Elson: The Crystal Structure of Protactinium Pentachloride. In: Acta Cryst. 1967, 22, pp. 85-89 ( doi: 10.1107 / S0365110X67000155 ).