|Name , symbol , atomic number||Protactinium, Pa, 91|
|Group , period , block||Ac , 7 , f|
|Appearance||bright, silvery, shiny metallic|
|Mass fraction of the earth's envelope||9 · 10 −8 ppm|
|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|
|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|
|Electronegativity||1.5 ( Pauling scale )|
|For other isotopes see list of isotopes|
|Hazard and safety information|
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.
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.
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.
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.
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 ).
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.
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 .
Protactinium is silvery metallic and becomes superconducting below 1.4 K.
Protactinium occurs mainly in two oxidation states , +4 and +5, both in solids and in solution.
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.
- The times given are half-lives .
→ Category: Protactinium compound
Protactinium (V) chloride (PaCl 5 ) forms yellow monoclinic crystals and has a chain structure consisting of 7-fold coordinated pentagonal bipyramids.
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.
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- Entry to Protactinium. In: Römpp Online . Georg Thieme Verlag, accessed on January 3, 2015.
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- Harry H. Binder: Lexicon of the chemical elements. S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 .
- The values for the properties (info box) are taken from www.webelements.com (Protactinium) , unless otherwise stated .
- CIAAW, Standard Atomic Weights Revised 2013 .
- 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.
- entry on protactinium at WebElements, https://www.webelements.com , accessed on June 13, 2020.
- 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.
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- Protactinium, Jefferson Lab
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