   #copyright

Francium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements

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               87                 radon ← francium → radium
               Cs
               ↑
               Fr
               ↓
               Uue

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                     Name, Symbol, Number francium, Fr, 87
                                             Chemical series alkali metals
                                              Group, Period, Block 1, 7, s
                                                       Appearance metallic
                                 Standard atomic weight (223)  g·mol^−1
                                          Electron configuration [Rn] 7s^1
                                Electrons per shell 2, 8, 18, 32, 18, 8, 1
                                                       Physical properties
                                                               Phase solid
                                   Density (near r.t.)  ? 1.87  g·cm^−3
                                                   Melting point  ? 300  K
                                                        (27 ° C, 80 ° F)
                                                   Boiling point  ? 950  K
                                                 (? 677 ° C, ? 1250 ° F)
                                       Heat of fusion ca. 2   kJ·mol^−1
                                Heat of vaporization ca. 65   kJ·mol^−1

   CAPTION: Vapor pressure (extrapolated)

                                         P(Pa)   1  10  100 1 k 10 k 100 k
                                        at T(K) 404 454 519 608 738   946

                                                         Atomic properties
                                     Crystal structure cubic body centered
                                                        Oxidation states 1
                                                    (strongly basic oxide)
                                     Electronegativity 0.7 (Pauling scale)
                                       Ionization energies 1st: 380 kJ/mol
                                                             Miscellaneous
                                                      Magnetic ordering  ?
                                       Electrical resistivity  ? 3 µΩ·m
                     Thermal conductivity (300 K)  ? 15  W·m^−1·K^−1
                                             CAS registry number 7440-73-5
                                                         Selected isotopes

                 CAPTION: Main article: Isotopes of francium

                                iso    NA   half-life DM  DE ( MeV)   DP
                               ^221Fr trace 4.8  min  α   6.457     ^217At
                               ^222Fr syn   14.2 min  β^- 2.033     ^222Ra
                               ^223Fr 100%  22.00 min β^- 1.149     ^223Ra
                                                      α   5.430     ^219At

                                                                References

   Francium ( IPA: /ˈfrænsiəm/), also referred to as eka-caesium and
   actinium K, is a chemical element in the periodic table that has the
   symbol Fr and atomic number 87. It has the lowest known
   electronegativity and is the second rarest naturally occurring element.
   Francium is a highly radioactive alkali metal that decays into
   astatine, radium, and radon; as an alkali metal, it has one valence
   electron.

   Marguerite Perey discovered francium in 1939. Of the elements added to
   the periodic table, francium was the last to have been discovered in
   nature before being synthesized. Outside the laboratory, francium is
   extremely rare, with trace amounts found in uranium and thorium ores.
   It exists naturally only as the isotopes francium-223 and francium-221.
   Francium can be synthesized by several methods, but none has yielded a
   weighable quantity of the element.

Characteristics

   Francium has the highest equivalent weight of any element. It is also
   the least stable of the first 101 elements: its most stable isotope,
   francium-223, has a half-life of less than 22 minutes. By contrast,
   astatine, the second-least stable element, has a maximum half-life of
   8.5 hours. All isotopes of francium decay into either astatine, radium,
   or radon. Francium has the lowest electronegativity of all the known
   elements at 0.7 on the Pauling scale. Caesium has the second-lowest at
   0.79. Liquid francium, if such a substance were created, would have a
   surface tension of 0.05092  J/ m^2 at its melting point.

   Francium is an alkali metal whose chemical properties most resemble
   those of caesium. As an alkali metal, francium has one valence
   electron. Francium coprecipitates with several caesium salts, such as
   caesium perchlorate, caesium picrate, and caesium chloroplatinate. This
   coprecipitation results in small amounts of francium perchlorate,
   francium picrate, and francium chloroplatinate. Nearly all francium
   salts are water-soluble.

Applications

   There are no commercial applications for francium due to its
   instability and rarity; it has only been used for research purposes,
   both in the fields of biology and atomic structure. Francium was once
   thought to be an aid in the diagnosis of cancerous diseases; but, this
   application has since been deemed impracticable.

   Francium's ability to be synthesized, trapped, and cooled, along with
   its relatively simple atomic structure have made it the subject of
   specialized spectroscopy experiments. These experiments have led to
   more specific information regarding energy levels and the coupling
   constants between subatomic particles. Studies on the light emitted by
   laser-trapped francium-210 ions have provided accurate data on
   transitions between atomic energy levels. These experimental results
   have been fairly similar to those predicted by quantum theory.

History

   As early as 1870, it was thought by chemists that there should be an
   alkali metal beyond caesium, with an atomic number of 87. It was then
   referred to by the provisional name eka-caesium. Research teams
   attempted to locate and isolate this missing element, and at least four
   false claims were made that the element had been found before an
   authentic discovery was made.

Erroneous discoveries

   Russian chemist D. K. Dobroserdov was the first scientist to claim to
   have found "eka-caesium". In 1925, he observed weak radioactivity in a
   sample of potassium, another alkali metal, and concluded that
   eka-caesium was contaminating the sample. He then published a thesis of
   his predictions of the properties of eka-caesium, in which he named the
   element russium after his home country. Shortly thereafter, Dobroserdov
   began to focus on his teaching career at the Polytechnic Institute of
   Odessa, and he did not pursue the element further.

   The following year, English chemists Gerald J. F. Druce and Frederick
   H. Loring analyzed X-ray photographs of manganese(II) sulfate. They
   observed spectral lines which they presumed to be of eka-caesium. They
   announced their discovery of element 87 and proposed the name
   alkalinium, as it would be the heaviest alkali metal.

   In 1930, Professor Fred Allison of the Alabama Polytechnic Institute
   claimed to have discovered element 87 when analyzing pollucite and
   lepidolite using his magneto-optical machine. Allison requested that it
   be named virginium after his home state of Virginia, along with the
   symbols Vi and Vm. In 1934, however, Professor MacPherson of UC
   Berkeley disproved the effectiveness of Allison's device and the
   validity of this false discovery.

   In 1936, Romanian chemist Horia Hulubei and his French colleague Yvette
   Cauchois also analyzed pollucite, this time using their high-resolution
   X-ray apparatus. They observed several weak emission lines which they
   presumed to be of element 87. Hulubei and Cauchois reported their
   discovery and proposed the name moldavium, along with the symbol Ml,
   after Moldavia, the Romanian province where they conducted their work.
   In 1937, Hulubei's work was criticized by American physicist F. H.
   Hirsh Jr., who rejected Hulubei's research methods. Hirsh was certain
   that eka-caesium would not be found in nature, and that Hulubei had
   instead observed mercury or bismuth X-ray lines. Hulubei, however,
   insisted that his X-ray apparatus and methods were too accurate to make
   such a mistake. Because of this, Jean Baptiste Perrin, Nobel Prize
   winner and Hulubei's mentor, endorsed moldavium as the true eka-caesium
   over Marguerite Perey's recently-discovered francium. Perey, however,
   continuously criticized Hulubei's work until she was credited as the
   sole discoverer of element 87.

Perey's analysis

   Eka-caesium was truly discovered in 1939 by Marguerite Perey of the
   Curie Institute in Paris, France, when she purified a sample of
   actinium-227 which had been reported to have a decay energy of 220 keV.
   However, Perey noticed decay particles with an energy level below
   80 keV. Perey thought this decay activity might have been caused by a
   previously unidentified decay product, one which was separated during
   purification, but emerged again out of the pure actinium-227. Various
   tests eliminated the possibility of thorium, radium, lead, bismuth, or
   thallium being the unknown element. The new product exhibited chemical
   properties of an alkali metal (such as co-precipitating with caesium
   salts), which led Perey to believe that it was element 87, caused by
   the alpha decay of actinium-227. Perey then attempted to determine the
   proportion of beta decay to alpha decay in actinium-227. Her first test
   put the alpha branching at .6%, which she later revised to 1%.

   Perey named the new isotope actinium-K, which we now refer to as
   francium-223, and in 1946, she proposed the name catium for her
   newly-discovered element, as she believed it to be the most
   electropositive cation of the elements. Irène Joliot-Curie, one of
   Perey's supervisors, opposed the name due to its connotation of cat
   rather than cation. Perey then suggested francium as an homage to the
   country in which she discovered it. This name was officially adopted by
   the International Union of Chemists in 1949. and assigned the symbol
   Fa; but, this abbreviation was revised to the current Fr shortly
   thereafter. Francium was the last naturally occurring element to be
   discovered, following rhenium in 1925. Further research into francium's
   structure was carried out by Sylvain Lieberman and his team at CERN in
   the 1970s and 1980s, among others.

Occurrence

Natural

   Francium-223 is the result of the alpha decay of actinium-227 and can
   be found in trace amounts in uranium and thorium minerals. In a given
   sample of uranium, there is estimated to be only one francium atom for
   every 1×10^18 uranium atoms. It is also calculated that there is at
   most 30  g of francium in the earth's crust at any time. This makes it
   the second rarest element in the crust after astatine.

Synthesized

   Francium can be synthesized in the nuclear reaction ^197Au + ^18O →
   ^210Fr + 5n. This process, developed by Stony Brook Physics, yields
   francium isotopes with masses of 209, 210, and 211, which are then
   isolated by the Magneto Optic Trap (MOT). Other synthesis methods
   include bombarding radium with neutrons, and bombarding thorium with
   protons, deuterons, or helium ions. No weighable amount of francium has
   been synthesized.

Isotopes

   There are 34 known isotopes of francium ranging in atomic mass from 199
   to 232. Francium has seven metastable nuclear isomers. Francium-223 and
   francium-221 are the only isotopes that occur in nature, though the
   former is far more common.

   Francium-223 is the most stable isotope with a half-life of
   21.8 minutes, and it is highly unlikely that an isotope of francium
   will ever be discovered or synthesized with one longer. Francium-223 is
   the fifth product of the actinium decay series as the daughter isotope
   of actinium-227. Francium-223 then decays into radium-223 by beta decay
   (1149 keV decay energy), with a minor (0.006%) alpha decay path to
   astatine-219 (5.4 MeV decay energy).

   Francium-221 has a half-life of 4.8 minutes. It is the ninth product of
   the neptunium decay series as a daughter isotope of actinium-225.
   Francium-221 then decays into astatine-217 by alpha decay (6.457 MeV
   decay energy).

   The least stable ground state isotope is francium-215, with a half-life
   of 0.12 μs. (9.54 MeV alpha decay to astatine-211): Its metastable
   isomer, francium-215m, is less stable still, with a half-life of only
   3.5 ns.
   Retrieved from " http://en.wikipedia.org/wiki/Francium"
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   with only minor checks and changes (see www.wikipedia.org for details
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