Francium is a
chemical element
A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...
with the
symbol
A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
Fr and
atomic number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
87. It is extremely
radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...
; its most stable isotope, francium-223 (originally called
actinium
Actinium is a chemical element with the symbol Ac and atomic number 89. It was first isolated by Friedrich Oskar Giesel in 1902, who gave it the name ''emanium''; the element got its name by being wrongly identified with a substance And ...
K after the natural
decay chain it appears in), has a half-life of only 22 minutes. It is the second-most
electropositive element, behind only
caesium
Caesium (IUPAC spelling) (or cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that a ...
, and is the
second rarest naturally occurring element (after
astatine
Astatine is a chemical element with the symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of astatine's isotopes are short-lived; ...
). The isotopes of francium decay quickly into astatine,
radium
Radium is a chemical element with the symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rather t ...
, and
radon
Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains through ...
. The
electronic structure of a francium atom is
n7s
1, and so the element is classed as an
alkali metal
The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...
.
Bulk francium has never been seen. Because of the general appearance of the other elements in its periodic table column, it is presumed that francium would appear as a highly reactive metal, if enough could be collected together to be viewed as a bulk solid or liquid. Obtaining such a sample is highly improbable, since the extreme heat of decay resulting from its short half-life would immediately vaporize any viewable quantity of the element.
Francium was discovered by
Marguerite Perey in France (from which the element takes its name) in 1939. Prior to its discovery, it was referred to as ''
eka-
caesium
Caesium (IUPAC spelling) (or cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that a ...
'' or ''ekacaesium'' because of its conjectured existence below caesium in the periodic table. It was the last element first discovered in nature, rather than by synthesis. Outside the laboratory, francium is extremely rare, with trace amounts found in
uranium
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
ores, where the
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
francium-223 (in the family of uranium-235) continually forms and decays. As little as 200–500 g exists at any given time throughout the
Earth's crust
Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...
; aside from francium-223 and francium-221, its other isotopes are entirely synthetic. The largest amount produced in the laboratory was a cluster of more than 300,000 atoms.
Characteristics
Francium is one of the most unstable of the naturally occurring elements: its longest-lived isotope, francium-223, has a
half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
of only 22 minutes. The only comparable element is
astatine
Astatine is a chemical element with the symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of astatine's isotopes are short-lived; ...
, whose most stable natural isotope, astatine-219 (the alpha daughter of francium-223), has a half-life of 56 seconds, although synthetic astatine-210 is much longer-lived with a half-life of 8.1 hours.
All isotopes of francium decay into astatine,
radium
Radium is a chemical element with the symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rather t ...
, or
radon
Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains through ...
.
Francium-223 also has a shorter half-life than the longest-lived isotope of each synthetic element up to and including element 105,
dubnium.
Francium is an alkali metal whose chemical properties mostly resemble those of caesium.
A heavy element with a single
valence electron, it has the highest
equivalent weight
In chemistry, equivalent weight (also known as gram equivalent) is the mass of one equivalent, that is the mass of a given substance which will combine with or displace a fixed quantity of another substance. The equivalent weight of an element is ...
of any element.
Liquid francium—if created—should have a
surface tension
Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to f ...
of 0.05092
N/m at its melting point.
Francium's melting point was estimated to be around ;
a value of is also often encountered.
The melting point is uncertain because of the element's extreme rarity and
radioactivity; a different extrapolation based on
Dmitri Mendeleev
Dmitri Ivanovich Mendeleev (sometimes transliterated as Mendeleyev or Mendeleef) ( ; russian: links=no, Дмитрий Иванович Менделеев, tr. , ; 8 February Old_Style_and_New_Style_dates">O.S._27_January.html" ;"title="O ...
's method gave . The estimated boiling point of is also uncertain; the estimates and , as well as the extrapolation from Mendeleev's method of , have also been suggested.
The density of francium is expected to be around 2.48 g/cm
3 (Mendeleev's method extrapolates 2.4 g/cm
3).
Linus Pauling
Linus Carl Pauling (; February 28, 1901August 19, 1994) was an American chemist, biochemist, chemical engineer, peace activist, author, and educator. He published more than 1,200 papers and books, of which about 850 dealt with scientific top ...
estimated the
electronegativity of francium at 0.7 on the
Pauling scale
Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the d ...
, the same as caesium; the value for caesium has since been refined to 0.79, but there are no experimental data to allow a refinement of the value for francium. Francium has a slightly higher
ionization energy
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...
than caesium, 392.811(4) kJ/mol as opposed to 375.7041(2) kJ/mol for caesium, as would be expected from
relativistic effects
Relativistic quantum chemistry combines relativistic mechanics with quantum chemistry to calculate elemental properties and structure, especially for the heavier elements of the periodic table. A prominent example is an explanation for the color of ...
, and this would imply that caesium is the less electronegative of the two. Francium should also have a higher
electron affinity
The electron affinity (''E''ea) of an atom or molecule is defined as the amount of energy released when an electron attaches to a neutral atom or molecule in the gaseous state to form an anion.
::X(g) + e− → X−(g) + energy
Note that this is ...
than caesium and the Fr
− ion should be more
polarizable than the Cs
− ion.
Compounds
Due to francium being very unstable, its salts are only known to a small extent. Francium
coprecipitates with several caesium
salts, such as
caesium perchlorate
Caesium perchlorate or cesium perchlorate (CsClO4), is a perchlorate of caesium. It forms white crystals, which are sparingly soluble in cold water and ethanol. It dissolves more easily in hot water.
CsClO4 is the second least soluble of the alk ...
, which results in small amounts of francium perchlorate. This coprecipitation can be used to isolate francium, by adapting the radiocaesium coprecipitation method of
Lawrence E. Glendenin
Lawrence Elgin Glendenin (November 8, 1918November 22, 2008) was an American chemist who co-discovered the element promethium.
Biography
Glendenin was born in Bay City, Michigan on November 8, 1918. He attended the University of Chicago, gradu ...
and C. M. Nelson. It will additionally coprecipitate with many other caesium salts, including the
iodate, the
picrate, the
tartrate (also
rubidium
Rubidium is the chemical element with the symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have a density higher ...
tartrate), the
chloroplatinate, and the
silicotungstate
Silicotungstic acid or tungstosilicic acid is a heteropoly acid with the chemical formula . It forms hydrates . In freshly prepared samples, ''n'' is approximately 29, but after prolonged desiccation, ''n'' = 6. It is a white solid although impu ...
. It also coprecipitates with
silicotungstic acid
Silicotungstic acid or tungstosilicic acid is a heteropoly acid with the chemical formula . It forms hydrates . In freshly prepared samples, ''n'' is approximately 29, but after prolonged desiccation, ''n'' = 6. It is a white solid although impur ...
, and with
perchloric acid
Perchloric acid is a mineral acid with the formula H Cl O4. Usually found as an aqueous solution, this colorless compound is a stronger acid than sulfuric acid, nitric acid and hydrochloric acid. It is a powerful oxidizer when hot, but aqueous sol ...
, without another alkali metal as a
carrier
Carrier may refer to:
Entertainment
* ''Carrier'' (album), a 2013 album by The Dodos
* ''Carrier'' (board game), a South Pacific World War II board game
* ''Carrier'' (TV series), a ten-part documentary miniseries that aired on PBS in April 20 ...
, which leads to other methods of separation.
[E. N K. Hyde ''Radiochemistry of Francium'', Subcommittee on Radiochemistry, National Academy of Sciences-National Research Council; available from the Office of Technical Services, Dept. of Commerce, 1960.]
Francium perchlorate
Francium perchlorate is produced by the reaction of
francium chloride
Francium chloride is a radioactive chemical compound with the formula FrCl. It is a salt predicted to be a white solid and is soluble in water. Its properties resemble caesium chloride.
Production
It is produced by the reaction of hydrochloric ac ...
and
sodium perchlorate
Sodium perchlorate is the inorganic compound with the chemical formula Na ClO4. It is a white crystalline, hygroscopic solid that is highly soluble in water and in alcohol. It is usually encountered as the monohydrate. The compound is noteworthy ...
. The francium perchlorate
coprecipitates with
caesium perchlorate
Caesium perchlorate or cesium perchlorate (CsClO4), is a perchlorate of caesium. It forms white crystals, which are sparingly soluble in cold water and ethanol. It dissolves more easily in hot water.
CsClO4 is the second least soluble of the alk ...
.
This coprecipitation can be used to isolate francium, by adapting the radiocaesium coprecipitation method of
Lawrence E. Glendenin
Lawrence Elgin Glendenin (November 8, 1918November 22, 2008) was an American chemist who co-discovered the element promethium.
Biography
Glendenin was born in Bay City, Michigan on November 8, 1918. He attended the University of Chicago, gradu ...
and C. M. Nelson. However, this method is unreliable in separating
thallium
Thallium is a chemical element with the Symbol (chemistry), symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists W ...
, which also coprecipitates with caesium.
Francium perchlorate's
entropy
Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynam ...
is expected to be 42.7
e.u (178.7 J mol
−1 K
−1).
Francium halides
Francium halides are all soluble in water and are expected to be white solids. They are expected to be produced by the reaction of the corresponding
halogen
The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group is ...
s. For example, francium chloride would be produced by the reaction of francium and
chlorine
Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...
. Francium chloride has been studied as a pathway to separate francium from other elements, by using the high
vapour pressure of the compound, although francium fluoride would have a higher vapour pressure.
Other compounds
Francium nitrate, sulfate, hydroxide, carbonate, acetate, and oxalate, are all soluble in water, while the
iodate,
picrate,
tartrate,
chloroplatinate, and
silicotungstate
Silicotungstic acid or tungstosilicic acid is a heteropoly acid with the chemical formula . It forms hydrates . In freshly prepared samples, ''n'' is approximately 29, but after prolonged desiccation, ''n'' = 6. It is a white solid although impu ...
are insoluble. The insolubility of these compounds are used to extract francium from other radioactive products, such as
zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'', ...
,
niobium
Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has sim ...
,
molybdenum
Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...
,
tin
Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal.
Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...
,
antimony
Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient time ...
, the method mentioned in the section above.
The CsFr molecule is predicted to have francium at the negative end of the dipole, unlike all known heterodiatomic alkali metal molecules. Francium
superoxide (FrO
2) is expected to have a more
covalent
A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...
character than its lighter
congeners; this is attributed to the 6p electrons in francium being more involved in the francium–oxygen bonding.
The relativistic destabilisation of the 6p
3/2 spinor may make francium compounds in oxidation states higher than +1 possible, such as
VF6">rVF6sup>−; but this has not been experimentally confirmed.
The only double salt known of francium has the formula Fr
9Bi
2I
9.
Isotopes
There are 34 known isotopes of francium ranging in
atomic mass
The atomic mass (''m''a or ''m'') is the mass of an atom. Although the SI unit of mass is the kilogram (symbol: kg), atomic mass is often expressed in the non-SI unit dalton (symbol: Da) – equivalently, unified atomic mass unit (u). 1&nbs ...
from 199 to 232.
Francium has seven
metastable nuclear isomers.
Francium-223 and francium-221 are the only isotopes that occur in nature, with the former being 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 with a longer half-life will ever be discovered or synthesized.
Francium-223 is a fifth product of the
uranium-235
Uranium-235 (235U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exis ...
decay series as a daughter isotope of
actinium-227;
thorium-227 is the more common daughter.
Francium-223 then decays into radium-223 by
beta decay
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
(1.149 MeV
decay energy), with a minor (0.006%)
alpha decay
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atom ...
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).
Although all primordial
237Np is
extinct
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
, the neptunium decay series continues to exist naturally in tiny traces due to (n,2n) knockout reactions in natural
238U.
The least stable
ground state
The ground state of a quantum-mechanical system is its stationary state of lowest energy; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state. ...
isotope is francium-215, with a half-life of 0.12 μs: it undergoes a 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.
Applications
Due to its instability and rarity, there are no commercial applications for francium.
It has been used for research purposes in the fields of
chemistry
Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...
and of
atomic structure
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons.
Every solid, liquid, gas, an ...
. Its use as a potential diagnostic aid for various
cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
s has also been explored,
but this application has been deemed impractical.
Francium's ability to be synthesized, trapped, and cooled, along with its relatively simple
atomic structure
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons.
Every solid, liquid, gas, an ...
, has made it the subject of specialized
spectroscopy
Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
experiments. These experiments have led to more specific information regarding
energy levels and the
coupling constant
In physics, a coupling constant or gauge coupling parameter (or, more simply, a coupling), is a number that determines the strength of the force exerted in an interaction. Originally, the coupling constant related the force acting between two ...
s between
subatomic particle
In physical sciences, a subatomic particle is a particle that composes an atom. According to the Standard Model of particle physics, a subatomic particle can be either a composite particle, which is composed of other particles (for example, a pr ...
s. 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
Quantum theory may refer to:
Science
*Quantum mechanics, a major field of physics
*Old quantum theory, predating modern quantum mechanics
* Quantum field theory, an area of quantum mechanics that includes:
** Quantum electrodynamics
** Quantum ch ...
.
History
As early as 1870, chemists thought that there should be an alkali metal beyond
caesium
Caesium (IUPAC spelling) (or cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that a ...
, with an atomic number of 87.
It was then referred to by the provisional name ''
eka-caesium''.
[Adloff, Jean-Pierre; Kaufman, George B. (September 25, 2005)]
Francium (Atomic Number 87), the Last Discovered Natural Element
. ''The Chemical Educator'' 10 (5). Retrieved on March 26, 2007. 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
Soviet chemist
Dmitry 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
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
, another alkali metal, and incorrectly concluded that eka-caesium was contaminating the sample (the radioactivity from the sample was from the naturally occurring potassium radioisotope,
potassium-40).
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
Odesa (also spelled Odessa) is the third most populous city and municipality in Ukraine and a major seaport and transport hub located in the south-west of the country, on the northwestern shore of the Black Sea. The city is also the administrativ ...
, and he did not pursue the element further.
The following year, English chemists
Gerald J. F. Druce and
Frederick H. Loring Frederick may refer to:
People
* Frederick (given name), the name
Nobility
Anhalt-Harzgerode
*Frederick, Prince of Anhalt-Harzgerode (1613–1670)
Austria
* Frederick I, Duke of Austria (Babenberg), Duke of Austria from 1195 to 1198
* Frederic ...
analyzed
X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
photographs of
manganese(II) sulfate
Manganese(II) sulfate usually refers to the inorganic compound with the formula MnSO4·H2O. This pale pink deliquescent solid is a commercially significant manganese(II) salt. Approximately 260,000 tonnes of manganese(II) sulfate were produced w ...
.
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,
Fred Allison
Fred C. Allison (July 4, 1882 – August 2, 1974) was an American physicist.
He developed a magneto-optic spectroscopy method that became known as the Allison magneto-optic method. He claimed to have discovered two new elements (later discredite ...
of the
Alabama Polytechnic Institute
Auburn University (AU or Auburn) is a public land-grant research university in Auburn, Alabama. With more than 24,600 undergraduate students and a total enrollment of more than 30,000 with 1,330 faculty members, Auburn is the second largest uni ...
claimed to have discovered element 87 (in addition to 85) when analyzing
pollucite and
lepidolite
Lepidolite is a lilac-gray or rose-colored member of the mica group of minerals with chemical formula . It is the most abundant lithium-bearing mineral and is a secondary source of this metal. It is the major source of the alkali metal rubidium.
...
using his
magneto-optical machine. Allison requested that it be named ''virginium'' after his home state of
Virginia
Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...
, along with the symbols Vi and Vm.
In 1934, H.G. MacPherson of
UC Berkeley
The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public university, public land-grant university, land-grant research university in Berkeley, California. Established in 1868 as the University of Californi ...
disproved the effectiveness of Allison's device and the validity of his discovery.
In 1936, Romanian physicist
Horia Hulubei
Horia Hulubei (; 15 November 1896 – 22 November 1972) was a Romanian nuclear physicist, known for his contributions to the development of X-ray spectroscopy.
Education and military service
Born in Iași, he graduated in 1915 first in his clas ...
and his French colleague
Yvette Cauchois
Yvette Cauchois (; 19 December 1908 – 19 November 1999) was a French physicist known for her contributions to x-ray spectroscopy and x-ray optics, and for pioneering European synchrotron research.
Education
Cauchois attended school in ...
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
Moldavia ( ro, Moldova, or , literally "The Country of Moldavia"; in Romanian Cyrillic: or ; chu, Землѧ Молдавскаѧ; el, Ἡγεμονία τῆς Μολδαβίας) is a historical region and former principality in Centr ...
, the Romanian province where Hulubei was born.
In 1937, Hulubei's work was criticized by American physicist
F. H. Hirsh Jr.
F is the sixth letter of the Latin alphabet.
F may also refer to:
Science and technology Mathematics
* F or f, the number 15 in hexadecimal and higher positional systems
* ''p'F'q'', the hypergeometric function
* F-distribution, a cont ...
, 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
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
or
bismuth X-ray lines. Hulubei insisted that his X-ray apparatus and methods were too accurate to make such a mistake. Because of this,
Jean Baptiste Perrin,
Nobel Prize
The Nobel Prizes ( ; sv, Nobelpriset ; no, Nobelprisen ) are five separate prizes that, according to Alfred Nobel's will of 1895, are awarded to "those who, during the preceding year, have conferred the greatest benefit to humankind." Alfr ...
winner and Hulubei's mentor, endorsed moldavium as the true eka-caesium over
Marguerite Perey's recently discovered francium. Perey took pains to be accurate and detailed in her criticism of Hulubei's work, and finally she was credited as the sole discoverer of element 87.
All other previous purported discoveries of element 87 were ruled out due to francium's very limited half-life.
Perey's analysis
Eka-caesium was discovered on January 7, 1939, by
Marguerite Perey of the
Curie Institute in Paris, when she purified a sample of
actinium
Actinium is a chemical element with the symbol Ac and atomic number 89. It was first isolated by Friedrich Oskar Giesel in 1902, who gave it the name ''emanium''; the element got its name by being wrongly identified with a substance And ...
-227 which had been reported to have a decay energy of 220 keV. 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
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high me ...
, radium,
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
, bismuth, or
thallium
Thallium is a chemical element with the Symbol (chemistry), symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists W ...
. 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, produced by the
alpha decay
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atom ...
of actinium-227.
Perey then attempted to determine the proportion of
beta decay
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
to alpha decay in actinium-227. Her first test put the alpha branching at 0.6%, a figure which she later revised to 1%.
Perey named the new isotope ''actinium-K'' (it is now referred to as francium-223)
and in 1946, she proposed the name ''catium'' (Cm) for her newly discovered element, as she believed it to be the most
electropositive cation
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
of the elements.
Irène Joliot-Curie, one of Perey's supervisors, opposed the name due to its connotation of ''cat'' rather than ''cation''; furthermore, the symbol coincided with that which had since been assigned to
curium
Curium is a transuranic, radioactive chemical element with the symbol Cm and atomic number 96. This actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first inte ...
.
Perey then suggested ''francium'', after France. This name was officially adopted by the
International Union of Pure and Applied Chemistry
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
(IUPAC) in 1949,
becoming the second element after
gallium
Gallium is a chemical element with the symbol Ga and atomic number 31. Discovered by French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in group 13 of the periodic table and is similar to the other metals of the group (aluminiu ...
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
hafnium
Hafnium is a chemical element with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri M ...
and
rhenium.
Further research into francium's structure was carried out by, among others,
Sylvain Lieberman Sylvain is the French form of Silvanus. It may refer to:
People
*Sylvain Archambault, Canadian director
*Sylvain Bied (1965–2011), French footballer and manager
*Sylvain Cappell (born 1946), American mathematician
*Sylvain Chavanel (born 1979), ...
and his team at
CERN
The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in a northwestern suburb of Gene ...
in the 1970s and 1980s.
Occurrence
223Fr is the result of the alpha decay of
227Ac and can be found in trace amounts in
uranium
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...
s.
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 a total mass of at most 30 g or, as other sources suggest, 340 to 550 g of francium in the
Earth's crust
Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...
at any given time.
Production
Francium can be synthesized by a
fusion reaction when a gold-197 target is bombarded with a beam of oxygen-18 atoms from a
linear accelerator in a process originally developed at the physics department of the
State University of New York at Stony Brook
Stony Brook University (SBU), officially the State University of New York at Stony Brook, is a public research university in Stony Brook, New York. Along with the University at Buffalo, it is one of the State University of New York system's ...
in 1995.
Depending on the energy of the oxygen beam, the reaction can yield francium isotopes with masses of 209, 210, and 211.
:
197Au +
18O →
209Fr + 6 n
:
197Au +
18O →
210Fr + 5 n
:
197Au +
18O →
211Fr + 4 n
The francium atoms leave the gold target as ions, which are neutralized by collision with
yttrium and then isolated in a
magneto-optical trap
A magneto-optical trap (MOT) is an apparatus which uses laser cooling and a spatially-varying magnetic field to create a trap which can produce samples of cold, trapped, neutral atoms. Temperatures achieved in a MOT can be as low as several microk ...
(MOT) in a gaseous unconsolidated state.
Although the atoms only remain in the trap for about 30 seconds before escaping or undergoing nuclear decay, the process supplies a continual stream of fresh atoms. The result is a
steady state containing a fairly constant number of atoms for a much longer time.
The original apparatus could trap up to a few thousand atoms, while a later improved design could trap over 300,000 at a time.
Sensitive measurements of the light emitted and absorbed by the trapped atoms provided 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. The research project using this production method relocated to
TRIUMF
TRIUMF is Canada's national particle accelerator centre. It is considered Canada's premier physics laboratory, and consistently regarded as one of the world's leading subatomic physics research centers. Owned and operated by a consortium of uni ...
in 2012, where over 10
6 francium atoms have been held at a time, including large amounts of
209Fr in addition to
207Fr and
221Fr.
Other synthesis methods include bombarding radium with neutrons, and bombarding thorium with protons,
deuterons
Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of a deuterium atom, called a deuteron, contains one proton and one n ...
, or
helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
s.
223Fr can also be isolated from samples of its parent
227Ac, the francium being milked via elution with NH
4Cl–CrO
3 from an actinium-containing cation exchanger and purified by passing the solution through a
silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
compound loaded with
barium sulfate
Barium sulfate (or sulphate) is the inorganic compound with the chemical formula Ba SO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium an ...
.
In 1996, the Stony Brook group trapped 3000 atoms in their MOT, which was enough for a video camera to capture the light given off by the atoms as they fluoresce.
Francium has not been synthesized in amounts large enough to weigh.
Notes
References
External links
Franciumat ''
The Periodic Table of Videos'' (University of Nottingham)
WebElements.com – Francium*
Scerri, Eric (2013). ''A Tale of Seven Elements'', Oxford University Press, Oxford,
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Chemical elements
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Eponyms
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Chemical elements with body-centered cubic structure
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