Francium

FRANCE-I am; Wed[lat. Francium] Chemical element (Fr), radioactive alkali metal.

◁ French, th, th.

(lat. Francium), a chemical element of group I of the periodic system, belongs to alkali metals. Radioactive, the most stable isotope 223 Fr (half-life 22 min). The name is from France - the homeland of M. Perey, who discovered the element. One of the rarest and least stable of all naturally occurring radioactive elements. The properties of francium have not been studied enough due to the impossibility of isolating significant amounts; by estimate: density 2.3-2.5 g / cm 3, t pl 18-21 ° C. Chemically the most reactive of all alkali metals.

FRANCIUM (lat. Francium), Fr (read "francium"), a radioactive chemical element with atomic number 87. Heaviest alkali metal. Located in group IA, in the 7th period of the periodic table of elements.
All radioisotopes of France decay rapidly, the longest-lived naturally occurring a-radioactive 223 Fr (T1 / 2 = 21.8 min) is included in the 235 U radioactive series. Isotopes with mass numbers 202-229 have been obtained. 7s outer layer electronic configuration 1. Oxidation state +1 (valence I). The radius of the atom is 0.29 nm, the radius of the Fr + ion is 0.178 nm. Pauling electronegativity (cm. POLING Linus) 0,7.
Being in nature
The content in the earth's crust is several hundred grams. 223 Fr is constantly produced by radioactive decay.
Discovery history
The first conclusion about the existence of Fr was made by D.I.Mendeleev (cm. MENDELEEV Dmitry Ivanovich)... In 1938-1939, Frenchwoman M. Perey discovered francium while studying the radioactive decay of 227 Ac. In 1945 the element was named in honor of M. Perey's homeland - France.
Physical and chemical properties
Since the researchers have at their disposal samples containing no more than 10 -13 -10 -14 g Fr, information on its properties is known only tentatively. Fr is similar in properties to cesium (cm. CESIUM)... Always co-crystallizes with its compounds. Density Fr can be 2.5 kg / dm 3, melting point 18-21 ° C, boiling point 640-660 ° C.

encyclopedic Dictionary. 2009 .

See what "francium" is in other dictionaries:

- (Francium), Fr, radioactive chemical element of group I of the periodic table, atomic number 87; alkali metal. France was discovered by the French radiochemist M. Pere in 1939 ... Modern encyclopedia

- (lat. Francium) Fr, chemical element of group I of the periodic table of Mendeleev, atomic number 87, atomic mass 223.0197, refers to alkali metals. Radioactive, the most stable isotope 223Fr (half-life 21.8 min). Named ... Big Encyclopedic Dictionary

- (symbol Fr), a radioactive, metallic element of the first group of the periodic table, discovered in 1939. The heaviest element in the series of ALKALINE METALS. It is naturally present in uranium ore, a decomposition product of ACTINIUM. The element is rare, ... ... Scientific and technical encyclopedic dictionary

Fr (named after France, the homeland of M. Pepe, who discovered the element; Latin Francium * a. Francium; N. Franzium; F. francium; and. Francio, francium), radioactive chemical. element of the I group of the Mendeleev system; at. n. 87. Has no stable isotopes. ... ... Geological encyclopedia

- (lat.Francium), Fr, radioactive. chem. element of the 1st group periodic. systems of elements, at. number 87 refers to alkali metals. Naim. stable from all radioactive substances. elements found in nature. Natural phosphorus consists of b radioactive 223Fr ... ... Physical encyclopedia

Noun., Number of synonyms: 2 metal (86) element (159) ASIS synonym dictionary. V.N. Trishin. 2013 ... Synonym dictionary

87 Radon ← Francium → Radium ... Wikipedia

- (lat. Francium), chem. element I gr. periodic system refers to alkali metals. Radioactive, naib. nuclide 223Fr is stable (half-life 22 min). Name from France, the homeland of M. Perey, who discovered the element. One of the rarest and least ... ... Natural science. encyclopedic Dictionary

Francium- Look Francie (Fr) ... Encyclopedic Dictionary of Metallurgy

francium- francis statusas T sritis chemija apibrėžtis Cheminis elementas. simbolis (iai) Fr atitikmenys: lot. francium angl. francium rus. francium ... Chemijos terminų aiškinamasis žodynas

Books

• Radioactive metals francium and dubnium. Methods for predicting physical parameters, Nikolaev OS .. The book contains methods for predicting the physical parameters of France and Dubnium. These are radioactive metals of the seventh period of DI Mendeleev's table. The short half-lives of these metals ...

Among the second - their neighbor in the periodic table, element number 87 - francium.

Francium is interesting for two reasons: first, it is the heaviest and most active alkali metal; Secondly, francium can be considered the most unstable of the first hundred elements of the periodic table The longest-lived isotope of france, 223 Fr, has a half-life of only 22 minutes. Such a rare combination in one element of high chemical activity with low nuclear resistance determined the difficulties in the discovery and study of this element.

How they looked for francium

It is not often that women scientists have the happiness of discovering new elements. Everyone knows the name of Maria Sklodowska-Curie, who discovered radium and polonium. Less well known is Ida Noddak (Takke), who discovered rhenium. The discovery of element number 87 is associated with the name of another woman - Frenchwoman Margarita Pere, by the way, a student of Maria Sklodowska-Curie. On January 9, 1939, she announced the discovery of element number 87. Let's go back, however, almost 70 years and consider the history of the discovery of this element in more detail.

The possibility of existence and the main properties of element no. 87 were predicted by D.I. Mendeleev. In 1871, in the article "The natural system of elements and its application to indicating the properties of undiscovered elements", published in the journal of the Russian Physicochemical Society, he wrote: "Then, in the tenth row, one can expect more basic elements belonging to I, II and III groups. The first of them should form the oxide R 2 O, the second - RO, and the third - R 2 O 3; the first will be similar to cesium, the second - to barium, and all their oxides must, of course, have the character of the most energetic bases. "

Based on the location of ecacesium in the periodic table, one would expect the metal itself to be liquid at room temperature, since cesium melts at 28 ° C. Due to the high reactivity, all terrestrial ecacesium should be found only in the form of salts, which in their solubility should exceed the salts of the remaining alkali metals, since when passing from lithium to cesium, the solubility of salts increases.

However, scientists of the 19th century failed to discover this interesting element. After the discovery of the radioactive neighbors of element 87, it became obvious that it must also be radioactive. But this did not clarify the situation either.

Scientists searching for the 87th element can be conditionally divided into two large groups. The first assumed the existence in nature of stable or long-lived isotopes of this element and therefore searched for it in minerals and concentrates of alkali metals, in the water of seas and oceans, in hay and mushroom ash, in molasses and cigar ash. The second group of scientists, focusing on the radioactivity of element No. 87, looked for it among the decay products of its neighboring elements.

When searching for ecacesium in the water of the seas and oceans, the water of the Dead Sea, which washes the lands of Palestine, was of particular interest. As a result of the expeditions, it was found that the water of this sea contains in significant quantities ions of alkali metals, halogens and other elements. "It is impossible to drown in the water of the Dead Sea," popular magazines reported. The English scientist I. Friend, who went to this region in July 1925, was interested in something else. “Already several years ago,” he wrote, “it occurred to me that if ecacesium was capable of permanent existence, then it could be found in the Dead Sea.”

All elements except alkaline were removed from water samples. Chlorides of alkali metals were separated by fractional precipitation. The ecacesium chloride was supposed to be the most soluble. However, the X-ray spectral analysis carried out at the last stage did not allow detecting ecacesium.

Nevertheless, several reports soon appeared in the literature about the discovery of the 87th element, but all of them were subsequently not confirmed. In 1926, English chemists J. Drews and F. Loring reported that they had observed lines of ecacesium on X-ray diffraction patterns of manganese sulfate, and suggested the name "alkalinium" for the newly discovered element. In 1929, the American physicist F. Allison, with the help of a basically erroneous method of magneto-optical analysis, discovered traces of the 87th element in rare minerals of alkali metals - pollucite and lepidolite. He called "his" element virginium. In 1931, the American scientists J. Papish and E. Weiner seem to have even isolated ecacesium from the samarskite mineral, and in 1937 the Romanian chemist G. Hulubei discovered ecacesium in the pollucite mineral and named it moldavium. But all these discoveries could not be confirmed, because the discoverers of alkalinium, Virginia and Moldavia, did not in the least take into account the most important property of ecacesium - its radioactivity.

However, failures also pursued the second group of scientists who were searching for the 87th element among the decay products of radioactive families. In none of the radioactive families known at that time - uranium 238 (4n + 2), uranium-235 (4n + 3) and thorium-232 (4n) - did the radioactive transformation lines pass through the isotopes of element 87. This could be for two reasons: either element 87 is a member of the missing series (4n + 1), or the process of radioactive decay of uranium-238 or uranium-235 in the radium-polonium section has not been thoroughly studied. Indeed, at the very beginning of a more thorough study of the uranium-238 series, it was discovered that the 214 Bi isotope can decay in two ways: undergo alpha decay, turning into 210T1, or beta decay, turning into the 214 Po isotope. This phenomenon is called forked decay, or radioactive fork. One could expect similar forks on the radium-polonium section.

The first message about the discovery of 87th element as a product of radioactive decay appeared in 1913 and belonged to the English chemist J. Cranston. Working with the preparation 228 Ac, he discovered the presence of weak alpha radiation in this isotope (in addition to the previously known beta radiation). As a result of alpha decay, 228 Ac is converted into an isotope of the 87th element - 224 87. Unfortunately, Cranston's message went unnoticed.

A year later, three Austrian radiochemists at once - Meyer, Hess and Paneth - observed the phenomenon of branched decay of the isotope 227 Ac, which belongs to the series of uranium-235 (4n + 3). They found alpha particles with a path length of 3.5 cm in air. "These particles are formed during the alpha decay of the usually beta-active 227 Ac," they reasoned, "... the decay product must be an isotope of element 87."

However, the conclusions of these scientists were reacted with suspicion. It was mainly caused by the fact that the observed alpha activity was very weak, and this was fraught with the possibility of error, especially since the actinium-227 preparation could contain an admixture of protactinium, and protactinium is capable of emitting such alpha particles.

Along with these experimental works, the theoretical study of the Odessa chemist D. Dobroserdov is of interest. In 1925, in the Ukrainian Chemical Journal, he published a message in which he expressed interesting considerations about the atomic weight, physical and chemical properties of the 87th element, and about where and by what methods to look for it. In particular, he stressed that ecacesium "must certainly be a very radioactive element." However, Dobroserdov made an unfortunate mistake, suggesting that the known radioactivity of potassium and rubidium is explained by the presence of ecacesium in them.

In the case of the discovery of an element with such interesting properties by Russian scientists, Dobroserdov proposed to call it Russium.

The following year, two works appeared at once: the outstanding radiochemists O. Gahn (Germany) and D. Hevesy (Hungary) attempted to prove the presence of ecatsium in the radioactive series. Hevesi studied the alpha decay of 228 Ac and 227 Ac, as well as the beta decay of emanations - isotopes of radon and showed that during beta decay of emanations, isotopes of the 87th element are not formed, and during the decay of actinium-228, if the isotope 224 87 is formed, then its number should be less than 1 / 200,000 of the original number of 228 Ac nuclei.

12 years passed, and at the end of 1938 the French chemist Margarita Pere, an employee of the Paris Institute of Radium, began to search for the 87th element. After repeating the experiments of Meyer, Hess and Paneth, she naturally also discovered alpha particles with a range of 3.5 cm. To prove that these mysterious particles are emitted by anemones and not protactinium, Pere very carefully purified the anemones from impurities and daughter products. By coprecipitation with tetravalent cerium hydroxide, she removed radioactinium, an isotope of thorium, from the solution; isotopes of radium were removed with barium carbonate, and anemones with lanthanum hydroxide.

The mother liquor remaining after such treatment could contain only alkaline and ammonium salts and, as it seemed, should not have been radioactive. However, the evaporation residue showed clear beta activity with a half-life of 22 minutes. It became clear that this activity is associated with some kind of alkaline element. It could be assumed that it arises as a result of the alpha decay of actinium and, according to the displacement rule, belongs to the nucleus of element no. 87. To prove this, Pere converted the activity into a precipitate together with cesium perchlorate. The activity of the obtained crystals of cesium perchlorate also decreased with a half-life of 22 minutes.

Thus, Pere discovered that there is a radioactive fork in 227 Ac: in 1.2% of decay cases, when alpha particles escape, a beta emitter is formed with the properties of a heavy alkali metal and a half-life of 22 minutes:

Long and painstaking work ended in success, and on September 9, 1939, Pere announced the discovery of element 87. In accordance with the nomenclature used for natural radioelements, she chose the name "anemones-K" for it. Later, in 1946, Pere named the element she discovered francium in honor of her homeland, and in 1949 the International Union of Pure and Applied Chemistry (IUPAC) approved this name and the symbol Fr.

How francium was explored

In addition to 283 Fr, several isotopes of element No. 87 are now known. But only 223 Fr is found in nature in any noticeable quantities. Using the law of radioactive decay, one can calculate that a gram of natural uranium contains 4 * 10 18 g of 223 Fr. And this means that in radioactive equilibrium with the entire mass of terrestrial uranium there is about 500 g of France-223. In vanishingly small quantities on Earth there are two more isotopes of element 87 - 224 Fr (a member of the radioactive family of thorium) and 221 Fr. Naturally, it is almost impossible to find an element on Earth whose world reserves do not reach a kilogram. Therefore, all studies of France and its few compounds were carried out on artificial products.

For a long time, Francium-223 was the only isotope that was used in experiments to study the chemical properties of element No. 87. Therefore, naturally, chemists were looking for methods for its accelerated isolation from 227 Ac. In 1953 M. Pere and the now famous French radiochemist J. Adlov developed an express method for the isolation of this isotope using paper chromatography. In this method, a 227 Ac solution containing 223 Fr is applied to the end of a paper strip, which is dipped into the elution solution. When the solution moves along the paper tape, radioelements are distributed over it. 223 Fr, being an alkali metal, moves with the solvent front and is deposited later than other elements. Later, Adlov suggested using a complex organic compound a-tenoyltrifluoroacetone (TTA) to isolate 223 Fr. Using the described method, in 10-40 minutes, it is possible to isolate a pure preparation of france-223. Due to the short half-life, it is possible to work with this drug for no more than two hours, after which a noticeable amount of daughter products is formed and it is necessary either to purify francium from them, or to isolate it again.

With the development of ion acceleration technology, new methods for producing francium were developed. When end-face or uranium targets are irradiated with high-energy protons, francium isotopes are also formed. The longest-lived of these was francium-212, with a half-life of 19.3 minutes. For 15 minutes of irradiation of a gram of uranium with a proton beam with an energy of 660 MeV at the synchrocyclotron of the Laboratory of Nuclear Problems of the Joint Institute for Nuclear Research in Dubna, 5 * 10 13 g of French-212 with an activity of 2.5-107 decays per minute are formed.

Isolation of france from irradiated targets is a very complicated process. In a very short time, it must be removed from a mixture containing almost all the elements of the periodic table. Several techniques for separating francium from irradiated uranium were developed by Soviet radiochemists A.K. Lavrukhina, A.A. Pozdnyakov I S.S. Rodin, and from irradiated thorium - by the American radiochemist E. Hyde. The selection of france is based on its coprecipitation with insoluble salts (perchlorate or cesium silicotungstate) or with free silicotungstic acid. The time of france extraction by these methods is 25-30 minutes.

Using all these methods, 27 isotopes of francium were obtained with mass numbers from 203 to 229.

Insofar as francium cannot be obtained in significant quantities, its physicochemical constants are most often calculated taking into account the properties of the other members of the alkali metal group. It was calculated that the melting point of francium is about 8 ° C, and the boiling point is about 620 ° C.

All experiments on the study of the chemical properties of france were carried out, naturally, with ultra-small amounts of this element. The solutions contained only 10 13 -10 9 g of France. At such concentrations, processes can become important that we usually forget about when dealing with macro quantities of a substance. For example, under these conditions, a radioactive isotope can be “lost” from the solution, being adsorbed on the walls of vessels, on the surface of sediments, on possible impurities ... Therefore, it would seem, when studying the properties of francium, one should operate with more concentrated solutions. But in this case, new difficulties arise due to the processes of radiolysis and ionization.

And yet, despite all the difficulties, some reliable data on the chemical properties of france have been obtained. The coprecipitation of francium with various insoluble compounds has been studied most fully. It is carried away from the solution by the chloroplatinates of cesium and rubidium Cs 2 PtCl 6 and Pb 2 PtCl 6, chloro-bismuthate Cs 2 BiCl 5, chlorostannate Cs 2 SnCl 6 and cesium chloroantimonate Cs2SbCl 5 * 2.5H 2 0, as well as free heteropolytoformic tungsten and phosphorus silicic acid - silica.

Francium is easily adsorbed on ion-exchange resins (sulfonic cation exchangers) from neutral and weakly acidic solutions. With these resins, it is easy to separate francium from most chemical elements. Here, perhaps, all the successes.

Application of France

Of course, one should not expect widespread use of element No. 87 in practice. And yet there is some benefit from France. First, with its help (by its radiation), it is possible to quickly determine the presence of anemones in natural objects; secondly, they hope to use francium for the early diagnosis of sarcomas. Preliminary experiments have been carried out to study the behavior of france in the organism of rats. It was found that francium selectively accumulates in tumors, and in the early stages of the disease. These results are very interesting, but only the future will show whether it will be possible to use them in oncological practice.

0.7 (Pauling scale)

Fr ← Fr + −2.92 V

~ 2 kJ / mol

~ 65 kJ / mol

31.6 J / (K mol)

cubic
body-centered

Being in nature

Francium is one of the rarest elements. Among the elements that constantly exist in the earth's crust, only astatine has a lower content. All natural francium is radiogenic, its radioactive decay is compensated by the simultaneous appearance of new francium atoms as intermediate decay products of uranium-235 and thorium-232. The total content of france in the earth's crust is estimated at 340 grams.

Isotopes

For 2012, 34 isotopes of france are known with mass numbers 199-232 and 7 metastable nuclear isomers. Nature (as products of radioactive decay of uranium and thorium) contains two isotopes: 223 Fr and 224 Fr. Francium-223 (the longest-lived of the isotopes of france, with a half-life of 22.3 minutes) is included in one of the side branches of the natural radioactive series of uranium-235 and is contained in extremely small quantities in uranium minerals. Studies of the properties of francium are carried out with indicator amounts of the nuclide 223 Fr (less than 10-15 g), since due to the absence of long-lived isotopes of francium, it is impossible to obtain in weight quantities. Formed by alpha decay of actinium-227:

227 Ac → 223 Fr (accompanied by α-radiation, decay probability approximately 1.4%),

The most common way to get france is by nuclear reaction:

$()\; ^\; (197)\; \_\; (79)\; \backslash \; textrm\; (Au)\; +\; ()\; ^\; (18)\; \_\; (8)\; \backslash \; textrm\; (O)\; \backslash \; rightarrow\; ()\; ^\; (210)\; \_\; (87)\; \backslash \; textrm\; (Fr)\; +\; (\; 5)\; ^\; (1)\; \_\; (0)\; \backslash \; textrm\; (n)$

Interestingly, this reaction uses gold. By this reaction, isotopes with mass numbers 209, 210 and 211 can be synthesized. However, all of these isotopes decay rapidly (the half-lives of 210 Fr and 211 Fr are three minutes, and 209 Fr are 50 seconds).

Physical and chemical properties

Francium is similar in properties to cesium. Always co-crystallizes with its compounds. Almost all French compounds are water-soluble. Relativistic effects 6p-shells make the bond of francium with oxygen in superoxides, for example, of the composition FrO 2, more covalent in comparison with superoxides of other alkali metals.

Since researchers have at their disposal only the smallest samples containing no more than 10 −7 g of francium, information on its physical properties can be determined only by calculation, based on data for stable alkali metals. According to these calculations, the density of francium at room temperature is 1.87 g / cm³, the melting point is 27 ° C, the boiling point is 677 ° C, and the specific heat of fusion is 9.385 kJ / kg.

Francium has the lowest electronegativity of any element currently known. Accordingly, francium is also the most reactive alkali metal.

Application

At present, francium and its salts have no practical application due to their short half-life and high radioactivity.

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- (Francium), Fr, radioactive chemical element of group I of the periodic table, atomic number 87; alkali metal. France was discovered by the French radiochemist M. Pere in 1939 ... Modern encyclopedia

- (lat. Francium) Fr, chemical element of group I of the periodic table of Mendeleev, atomic number 87, atomic mass 223.0197, refers to alkali metals. Radioactive, the most stable isotope 223Fr (half-life 21.8 min). Named ... Big Encyclopedic Dictionary

- (symbol Fr), a radioactive, metallic element of the first group of the periodic table, discovered in 1939. The heaviest element in the series of ALKALINE METALS. It is naturally present in uranium ore, a decomposition product of ACTINIUM. The element is rare, ... ... Scientific and technical encyclopedic dictionary

Fr (named after France, the homeland of M. Pepe, who discovered the element; Latin Francium * a. Francium; N. Franzium; F. francium; and. Francio, francium), radioactive chemical. element of the I group of the Mendeleev system; at. n. 87. Has no stable isotopes. ... ... Geological encyclopedia

- (lat.Francium), Fr, radioactive. chem. element of the 1st group periodic. systems of elements, at. number 87 refers to alkali metals. Naim. stable from all radioactive substances. elements found in nature. Natural phosphorus consists of b radioactive 223Fr ... ... Physical encyclopedia

Noun., Number of synonyms: 2 metal (86) element (159) ASIS synonym dictionary. V.N. Trishin. 2013 ... Synonym dictionary

I AM; Wed [lat. Francium] Chemical element (Fr), radioactive alkali metal. ◁ Francis, oh, oh. * * * Francium (lat. Francium), a chemical element of group I of the periodic table, belongs to alkali metals. Radioactive, most stable ... ... encyclopedic Dictionary

- (lat. Francium), chem. element I gr. periodic system refers to alkali metals. Radioactive, naib. nuclide 223Fr is stable (half-life 22 min). Name from France, the homeland of M. Perey, who discovered the element. One of the rarest and least ... ... Natural science. encyclopedic Dictionary

Francium- Look Francie (Fr) ... Encyclopedic Dictionary of Metallurgy

francium- francis statusas T sritis chemija apibrėžtis Cheminis elementas. simbolis (iai) Fr atitikmenys: lot. francium angl. francium rus. francium ... Chemijos terminų aiškinamasis žodynas

Books

• Radioactive metals francium and dubnium. Methods for predicting physical parameters, Nikolaev OS .. The book contains methods for predicting the physical parameters of France and Dubnium. These are radioactive metals of the seventh period of DI Mendeleev's table. The short half-lives of these metals ...
• De Gaulle and Gaullists. "The Constable" and his associates, Vladlen Maksimov. The book tells about the most famous French of the XX century, the founder and first president of the Fifth Republic from a critical side unusual and unexpected for the Russian reader. Author in detail ...

DEFINITION

Francium located in the seventh period I group of the main (A) subgroup of the Periodic table.

Refers to elements s-families. Metal. Designation - Fr. Serial number - 87. Relative atomic mass - 223.02 amu.

Electronic structure of the atom france

The francium atom consists of a positively charged nucleus (+87), inside which there are 87 protons and 136 neutrons, and around, in seven orbits, 87 electrons move.

Fig. 1. Schematic structure of the atom of France.

The orbital distribution of electrons is as follows:

87Fr) 2) 8) 18) 32) 32) 8) 1;

1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4f 14 5s 2 5p 6 5d 10 6s 2 6p 6 7s 1 .

At the outer electronic level of the francium atom, there is 1 electron, which is valence (located at the 7s-sublevel). The energy diagram of the ground state takes the following form:

The presence of one unpaired electron in a francium atom indicates its ability to exhibit an oxidation state of +1.

The valence electron of the francium atom can be characterized by a set of four quantum numbers: n(main quantum), l(orbital), m l(magnetic) and s(spin):

Examples of problem solving

EXAMPLE 1