   #copyright

Protactinium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


              91              thorium ← protactinium → uranium
              Pr
             ↑
             Pa
             ↓
             (Uqu)

                                  Periodic Table - Extended 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] 5f^2 6d^1 7s^2
                                Electrons per shell 2, 8, 18, 32, 20, 9, 2
                                                       Physical properties
                                                               Phase solid
                                      Density (near r.t.) 15.37 g·cm^−3
                                                     Melting point 1841  K
                                                    (1568 ° C, 2854 ° F)
                                                   Boiling point  ? 4300 K
                                                     (? 4027 ° C, ? ° F)
                                         Heat of fusion 12.34 kJ·mol^−1
                                     Heat of vaporization 481 kJ·mol^−1
                                                         Atomic properties
                                            Crystal structure orthorhombic
                                                        Oxidation states 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^−1·K^−1
                                             CAS registry number 7440-13-3
                                                         Selected isotopes

   CAPTION: 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

                                                                References

   Protactinium ( IPA: /ˌprəʊˌtakˈtɪniəm/) is a chemical element in the
   periodic table that has the symbol Pa and atomic number 91.

Notable Characteristics

   Protactinium is a silver metallic element that belongs to the actinide
   group, with a bright metallic luster that it retains for some time in
   the air. It is superconductive at temperatures below 1.4 K.

Applications

   Due to its scarcity, high radioactivity and toxicity, there are
   currently no uses for protactinium outside of basic scientific
   research.

   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 kg. Other authors conclude
   that no chain reactions are possible in Protactinium-231.

History

   Protactinium was first identified in 1913, when Kasimir Fajans and O.
   H. Göhring encountered short-lived isotope 234m-Pa, with a half-life of
   about 1.17 minutes, during their studies of the decay chain of 238-U.
   They gave the new element the name Brevium (Latin brevis, brief,
   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 231-Pa, and
   shortened to Protactinium in 1949.

   Aristid V. Grosse prepared 2 mg of Pa[2]O[5] in 1927, and later on
   managed to isolate Protactinium for the first time in 1934 from 0.1 mg
   of Pa[2]O[5], first converting the oxide to an iodide and then cracking
   it in a high vacuum by an electrically heated filament by the reaction
   2PaI[5] → 2Pa + 5I[2].

   In 1961, the United Kingdom Atomic Energy Authority was able to produce
   125 g of 99.9% pure protactinium, 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 is reported
   that the metal was sold to laboratories for a cost of 2,800 USD / g in
   the following years.

Biological Role

   Protactinium does not play any biological role.

Occurrence

   Protactinium occurs in pitchblende to the extent of about 1 part ^231Pa
   to 10 million of ore. Some ores from the Democratic Republic of the
   Congo have about 3 ppm.

Compounds

   Known protactinium compounds include:
     * Fluorides
          + PaF[4]
          + PaF[5]
     * Chlorides
          + PaCl[4]
          + PaCl[5]
     * Bromides
          + PaBr[4]
          + PaBr[5]
     * Iodides
          + PaI[3]
          + PaI[4]
          + PaI[5]
     * Oxides
          + PaO
          + PaO[2]
          + Pa[2]O[5]

Isotopes

   29 radioisotopes of protactinium have been characterized, with the most
   stable being 231-Pa with a half life of 32760 years, 233-Pa with a
   half-life of 26.967 days, and 230-Pa with a half-life of 17.4 days. All
   of the remaining radioactive isotopes have half-lifes that are less
   than 1.6 days, and the majority of these have half lifes that are less
   than 1.8 seconds. This element also has 2 meta states, 217m-Pa (t[½]
   1.15 milliseconds) and 234m-Pa (t[½] 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 element Ac (actinium) isotopes and the
   primary products after are element U (uranium) isotopes.

Precautions

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

   Retrieved from " http://en.wikipedia.org/wiki/Protactinium"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
