performed the: .
4.1 Erroneous and incomplete discoveries
4.2 Perey's analysis
(pronounced /ˈfrænsiəm/, FRAN-see-əm), formerly known as
eka-caesium and actinium K, is a chemical element that has the symbol Fr and
atomic number 87. It has one of the lowest electronegativity of all known
elements, and is the second rarest naturally occurring element (after astatine).
Francium is a highly radioactive metal that decays into astatine, radium, and
radon. As an alkali metal, it has one valence electron. Francium was discovered by Marguerite
Perey in France (from which the element takes its name) in 1939. It was the
last element discovered in nature, rather than synthesized. Outside the
laboratory, francium is extremely rare, with trace amounts found in uranium and
thorium ores, where the isotope francium-223 continually forms and decays. As
little as 20-30 g (one ounce) exists at any given time throughout the Earth's
crust; the other isotopes are entirely synthetic. The largest amount ever
collected of any isotope was a cluster of about 10,000 atoms (of francium-210)
created as an ultracold gas at Stony Brook in 1997. General properties
number francium, Fr, 87
category alkali metal
block 1, 7, s
atomic weight (223) g·mol−1
configuration [Rn] 7s1
shell 2, 8, 18, 32, 18, 8, 1 (Image)
r.t.) 1.87 g·cm−3
? 300 K, ? 27 °C, ? 80 °F
? 950 K, ? 677 °C, ? 1250 °F
Heat of fusion
ca. 2 kJ·mol−1
vaporization ca. 65 kJ·mol−1
the least stable of the naturally occurring elements: its most stable isotope,
francium-223, has a maximum half-life of only 22 minutes. In contrast,
astatine, the second-least stable naturally occurring element, has a maximum
half-life of 8.5 hours. All isotopes of francium decay into either astatine,
radium, or radon. Francium is also less stable than all synthetic elements
up to element 105.
Francium is an
alkali metal whose chemical properties most resemble those of caesium. A very
heavy element with a single valence electron, it has the highest equivalent
weight of any element. Liquid francium — if such a substance were to be
created — should have a surface tension of 0.05092 N/m at its melting point.
Francium’s melting point was claimed to have been calculated to be around 27 °C (80 °F, 300 K). However, the melting point is uncertain because of the element’s extreme
rarity and radioactivity. This melting point may have been in limited
precision, or so much heat produced from radioactivity that its calculated
melting point may have been overestimated. However, the melting point of
francium is estimated to be about 22 °C (71 °F, 295 K), based from the periodic trends in melting points with other alkali
metals. Also the boiling point may have been overestimated at
around 677 °C (1250 °F, 950 K). Based from the periodic trends with other
alkali metals, the boiling point of francium is estimated to be between 660 to 665 °C (1220 to 1230 °F, 935 to 940 K). Because radioactive elements give
off heat Francium would almost certainly be a liquid if enough visible Francium
were to be produced.
estimated the electronegativity of francium at 0.7 on the Pauling scale, the
same as caesium; the value for caesium has since been refined to 0.79,
although there are no experimental data to allow a refinement of the value for
francium. Francium has a slightly higher ionization energy than caesium,
392.811(4) kJ/mol as opposed to 375.7041(2) kJ/mol for caesium, as would be
expected from relativistic effects, and this would imply that caesium is the
less electronegative of the two.
coprecipitates with several caesium salts, such as caesium perchlorate, which
results in small amounts of francium perchlorate. This coprecipitation can be
used to isolate francium, by adapting the radiocaesium coprecipitation method
of Glendenin and Nelson. It will additionally coprecipitate with many other
caesium salts, including the iodate, the picrate, the tartrate (also rubidium
tartrate), the chloroplatinate, and the silicotungstate. It also coprecipitates
with silicotungstic acid, and with perchloric acid, without another alkali
metal as a carrier, which provides other methods of separation. Nearly
all francium salts are water-soluble.
Due to its
instability and rarity, there are no commercial applications for francium.
It has been used for research purposes in the fields of biology  and of
atomic structure. Its use as a potential diagnostic aid for various cancers has
also been explored, but this application has been deemed impractical.
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 which are fairly
similar to those predicted by quantum theory.
As early as
1870, chemists thought 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 and incomplete discoveries
D.K. Dobroserdov was the
first scientist to claim to have found eka-caesium, or francium. 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 on 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.
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
In 1930, 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, H.G. 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 those 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.
was 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 the unknown element being thorium, radium, lead,
bismuth, or thallium. The new product exhibited chemical properties of an
alkali metal (such as coprecipitating 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 0.6%, a figure which
she later revised to 1%.
the new isotope actinium-K (now referred 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, after
France. This name was officially adopted by the International Union of Pure
and Applied Chemistry in 1949, becoming the second element after gallium to
be named after France. It was assigned the symbol Fa, but this abbreviation was
revised to the current Fr shortly thereafter. Francium was the last element
discovered in nature, rather than synthesized, following rhenium in 1925.
Further research into francium's structure was carried out by, among others,
Sylvain Lieberman and his team at CERN in the 1970s and 1980s.
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 1×1018 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.
This sample of uraninite contains about 100,000 atoms (3.3 ? 10?20 g) of 223Fr at any given time.
be synthesized in the nuclear reaction 197Au + 18O → 210Fr + 5n
developed by Stony Brook Physics, yields francium isotopes with masses of 209,
210, and 211, which are then isolated by the magneto-optical trap
(MOT). The production rate of a particular isotope depends on the energy of
the oxygen beam. An 18O beam from the Stony Brook LINAC creates 210Fr in the
gold target with the nuclear reaction 197Au + 18O = 210Fr + 5n. The production
required some time to develop and understand. It was critical to operate the
gold target very close to its melting point and to make sure that its surface
was very clean. The nuclear reaction imbeds the francium atoms deep in the gold
target, and they must be removed efficiently. The atoms diffuse fast to the
surface of the gold target and are released as ions. The francium ions are
guided by electrostatic lenses until they land into a surface of hot yttrium
and become neutral again. The francium is then injected into a glass bulb. A
magnetic field and laser beams cool and confine the atoms. Although the atoms
remain in the trap for only about 20 seconds before escaping (or decaying), a
steady stream of fresh atoms replaces those lost, keeping the number of trapped
atoms roughly constant for minutes or longer. Initially, about 1000 francium
atoms were trapped in the experiment. This was gradually improved and is
capable of trapping over 300,000 neutral atoms of francium a time. Although
these are neutral "metallic" atoms ("francium metal"), they
in a gaseous unconsolidated state. Enough francium is trapped that a video
camera can capture the light given off by the atoms as they fluoresce. The atoms
appear as a glowing sphere about 1 millimeter in diameter. This was the very first time that anyone had ever seen francium. The
researchers can now make extremely sensitive measurements of the light emitted and
absorbed by the trapped atoms, providing the first experimental results on
various transitions between atomic energy levels in francium. Initial
measurements show very good agreement between experimental values and
calculations based on quantum theory. Other synthesis methods include
bombarding radium with neutrons, and bombarding thorium with protons,
deuterons, or helium ions. Francium has not yet, as of 2009[update], been
synthesized in amounts large enough to weigh.
Neutral francium atoms can be trapped in the MOT using a magnetic field and
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.
is the most stable isotope with a half-life of 21.8 minutes, and it is
highly unlikely that an isotope of francium with a longer half-life will ever
be discovered or synthesized. 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).
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).
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.
individual representative of the periodic table of chemical elements Dmitry
Ivanovich Mendeleyev, the element has unique chemical and physical properties
Element is of
great economic importance and plays a major role in world culture
the least unstable isotope, Fr-223
synthetic elements, like technetium, have later been found in nature.
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