Francium (eka-cesium) is an element of the main subgroup of the first group of the seventh period of the periodic system of chemical elements of D.I. Mendeleev, with atomic number 87. Denoted by the symbol Fr (lat. Francium). The simple substance francium (CAS number: 7440-73-5) is a radioactive alkali metal with high chemical activity.

Story

This element was predicted by D.I. Mendeleev (as Eka-cesium), and was discovered (by its radioactivity) in 1939 by Marguerite Pere, an employee of the Radium Institute in Paris. She gave it the name in 1964 in honor of her homeland - France.

Receipt

Microscopic amounts of francium-223 and francium-224 can be chemically isolated from uranium and thorium minerals. Other isotopes of francium are produced artificially using nuclear reactions.
The most common way to obtain francium by nuclear reaction: 197 Au + 18 O → 210 Fr + 5n
Interestingly, this reaction uses gold. Using this reaction, isotopes with mass numbers 209, 210 and 211 can be synthesized. However, all of these isotopes decay quickly (the half-life of 210 Fr and 211 Fr is three minutes, and 209 Fr is 50 seconds).

Physical and chemical properties

Francium is similar in properties to cesium. Always co-crystallizes with its compounds. Since researchers have at their disposal only the smallest samples containing no more than 10 -7 g of francium, information about its properties is known with a fairly large error, but it is constantly being refined. According to the latest data, 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 chemically active alkali metal.

Among the second is their neighbor in the periodic table, element No. 87 - francium.

Francium is interesting for two reasons: firstly, 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, francium, 223 Fr, has a half-life of only 22 minutes. Such a rare combination in one element of high chemical activity with low nuclear stability determined the difficulties in the discovery and study of this element.

How they searched for France

Women scientists do not often have the fortune of discovering new elements. Everyone knows the name of Marie Sklodowska-Curie, who discovered radium and polonium. Less well known is Ida Noddak (Tacke), who discovered rhenium. The discovery of element No. 87 is associated with the name of another woman - the Frenchwoman Marguerite Peret, by the way, a student of Marie Sklodowska-Curie. On January 9, 1939, she announced the discovery of element No. 87. Let us, however, go back almost 70 years and consider the history of the discovery of this element in more detail.

The possibility of existence and basic 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 Physical-Chemical Society, he wrote: “Then in the tenth row one can still wait for the 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 cesium 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 excesium should be found only in the form of salts, which in their solubility should exceed the salts of other alkali metals, since when moving from lithium to cesium, the solubility of the salts increases.

However, scientists of the 19th century failed to discover this interesting element. After the discovery of element 87's radioactive neighbors, it became obvious that it too must be radioactive. But this did not clear up the situation.

Scientists who searched for the 87th element can be 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 the ashes of hay and mushrooms, in molasses and cigar ashes. 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 excasium in the waters 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 significant quantities of 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 these parts in July 1925, was interested in something else. “Already several years ago,” he wrote, “it occurred to me that if ekacesium was capable of permanent existence, then it could be found in the Dead Sea.”

All elements except alkaline ones were removed from water samples. Alkali metal chlorides were separated by fractional precipitation. Ekacesium chloride should have been the most soluble. However, the X-ray spectral analysis carried out at the last stage did not allow the detection of excretion.

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 excasium in X-ray diffraction patterns of manganese sulfate, and proposed the name “alkalinium” for the newly discovered element. In 1929, the American physicist F. Allison, using a fundamentally erroneous method of magneto-optical analysis, discovered traces of element 87 in rare alkali metal minerals - pollucite and lepidolite. He named “his” element virginium. In 1931, American scientists J. Papish and E. Weiner even seemed to isolate excasium from the mineral samarskite, and in 1937, the Romanian chemist G. Hulubey discovered excesium in the mineral pollucite and named it moldavium. But all these discoveries could not be confirmed, because the discoverers of alkalinium, Virginia and Moldova, did not take into account the most important property of excasium - its radioactivity.

However, failures also plagued the second group of scientists 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 lines of radioactive transformations pass through the isotopes of the 87th element. This could be for two reasons: either element No. 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, already 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 branched decay, or radioactive fork. One could expect similar forks in the radium-polonium section.

The first report of the discovery of element 87 as a product of radioactive decay appeared back in 1913 and belonged to the English chemist J. Cranston. Working with the 228 Ac preparation, 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, 228Ac turns into the isotope of the 87th element - 22487. Unfortunately, Cranston's message fell on deaf ears.

A year later, three Austrian radiochemists - Meyer, Hess and Paneth - observed the phenomenon of branched decay of the isotope 227Ac, ​​belonging to the uranium-235 series (4n+3). They discovered alpha particles with a path length in air of 3.5 cm. “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, many treated the conclusions of these scientists with distrust. It was caused mainly 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 similar alpha particles.

Along with these experimental works, the theoretical research 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 thoughts about the value of the atomic weight, the physical and chemical properties of the 87th element, and where and by what methods one should look for it. In particular, he emphasized that excasium “must certainly be a very radioactive element.” However, Dobroserdov made an unfortunate mistake in assuming that the known radioactivity of potassium and rubidium was explained by the presence of excesium in them.

In the event of the discovery of an element with such interesting properties by Russian scientists, Dobroserdov proposed calling it russium.

The following year, two works appeared at once: outstanding radiochemists O. Hahn (Germany) and D. Hevesy (Hungary) attempted to prove the presence of excasium in radioactive series. Hevesy 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 the 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 quantity should be less than 1/200,000 of the original number of 228 Ac cores.

12 years passed, and at the end of 1938, the French chemist Margarita Pere, an employee of the Paris Radium Institute, began searching for the 87th element. 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 were emitted by actinium and not protactinium, Pere very carefully purified the sea anemone from impurities and daughter products. By co-precipitation with tetravalent cerium hydroxide, she removed radioactinium, an isotope of thorium, from the solution; Isotopes of radium were derived with barium carbonate, and actinium 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, beta activity was clearly detected in the evaporation residue with a half-life of 22 minutes. It became clear that this activity was associated with some alkaline element. It could be assumed that it arises from the alpha decay of actinium and, according to the displacement rule, belongs to the nucleus of element No. 87. To prove this, Pere transferred the activity to a precipitate with cesium perchlorate. The activity of the resulting cesium perchlorate crystals 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, the emission of alpha particles produces a beta emitter with the properties of a heavy alkali metal and a half-life of 22 minutes:

The long and painstaking work was successful, and on September 9, 1939, Pere announced the discovery of element No. 87. In accordance with the nomenclature used for natural radioelements, she chose the name “actinium-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 studied

In addition to 283 Fr, several isotopes of element No. 87 are now known. But only 223 Fr exists in nature in any noticeable quantities. Using the law of radioactive decay, we can calculate that a gram of natural uranium contains 4*10 18 g of 223 Fr. This means that about 500 g of France-223 is in radioactive equilibrium with the entire mass of earthly uranium. There are two more isotopes of element No. 87 in vanishingly small quantities on Earth - 224 Fr (a member of the radioactive thorium family) and 221 Fr. Naturally, it is almost impossible to find an element on Earth whose global reserves do not reach a kilogram. Therefore, all studies of francium and its few compounds were performed 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. Peret and the now famous French radiochemist J. Adlov developed an express method for isolating this isotope using paper chromatography. In this method, a solution of 227 Ac containing 223 Fr is applied to the end of a paper tape, which is immersed in the elution solution. When the solution moves along the paper tape, radioelements are distributed along it. 223 Fr, being an alkali metal, moves with the solvent front and is deposited later than other elements. Later, Adlov proposed using the complex organic compound a-thenoyltrifluoroacetone (TTA) to isolate 223 Fr. Using the described method, it is possible to isolate pure France-223 in 10-40 minutes. Due to the short half-life, you can work with this drug for no more than two hours, after which a noticeable amount of daughter products is formed and you need to either purify francium from them or 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 them was francium-212 with a half-life of 19.3 minutes. In 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 France-212 are formed with an activity of 2.5-107 decays per minute.

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

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

Because the francium cannot be obtained in significant quantities, its physicochemical constants are most often calculated taking into account the properties of the remaining 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 to study the chemical properties of francium were carried out, naturally, with ultra-small quantities of this element. The solutions contained only 10 13 -10 9 g of francium. At such concentrations, processes that we usually forget about when dealing with macro quantities of a substance can become important. For example, under these conditions, a radioactive isotope can be “lost” from solution, adsorbed on the walls of vessels, on the surface of sediments, on possible impurities... Therefore, it would seem that 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 francium have been obtained. The coprecipitation of francium with various insoluble compounds has been most fully studied. It is carried away from the solution by cesium and rubidium chloroplatinates Cs 2 PtCl 6 and Pb 2 PtCl 6, chlorobismuthate Cs 2 BiCl 5, chlorostanate Cs 2 SnCl 6 and cesium chloroantimonate Cs2SbCl 5 * 2.5H 2 0, as well as free heteropolyacids - silicotungstic and phosphotungstic.

Francium is easily adsorbed on ion exchange resins (sulfonic cation exchangers) from neutral and slightly acidic solutions. With the help of these resins it is easy to separate francium from most chemical elements. That, perhaps, is all the success.

Application France

Of course, one cannot expect widespread use of element No. 87 in practice. And yet there are benefits from France. Firstly, with its help (by its radiation) you can quickly determine the presence of actinium in natural objects; secondly, they hope to use francium for the early diagnosis of sarcomas. Preliminary experiments were carried out to study the behavior of francium in the body of rats. It was found that francium selectively accumulates in tumors, including in the early stages of the disease. These results are very interesting, but only the future will tell whether they will be able to be used in oncological practice.

Mendeleev's elements. By 1925 it was one of four elements not found. It is the heaviest and most active existing in nature, and it is also the fastest to half-life of existing chemical elements. This, and the low nuclear stability, made it impossible for a long time to discover francium, the existence of which was predicted by Mendeleev almost a century before its discovery.

History of the discovery of the chemical element France

It is distinctive in that it fell to the fate of a woman whose name is Margarita Pere. The search for this substance was based on Based on the substances adjacent to No. 87, various hypotheses were put forward about the properties of this metal:

• due to the fact that neighboring cesium melts at room temperature, it was assumed that element 87 would also melt at low temperatures;
• it was believed that it would refer to such liquid metals as cesium or mercury;
• hypotheses were put forward about its radioactivity.

By the end of 1938, Margarita Pere joined the search for this substance. She focused her attention on the alpha particles emitted by actinium. She thoroughly purified this substance from various impurities, leaving only a pure element. After lengthy chemical treatments, the scientist’s hands remained containing alkaline salts. She assumed that it was not radioactive, but after evaporation, beta activity became clearly visible with a half-life of 22 minutes. It immediately became clear to the woman that such a speed depends directly on the action of the alkaline element.

Margarita's long work was crowned with success only in the fall of 1939. Based on the existing nomenclature, the woman gave the 87th element the name “Actinium-K,” which she later renamed francium in memory of the place in which she was born. The International Union of Pure and Applied Chemistry adopted the name coined by Margarita Pere. This is how France was discovered.

Chemical element Fr: characteristics

It is the heaviest and most reactive alkali metal existing in nature, and it is also one of the fastest half-lives of any existing chemical element. The longest-lived of its isotopes can be found in uranium minerals. Therefore, the chemical element francium is very poorly studied, as it decays quickly. Moreover, it has very high radioactivity. But still, small quantities of this element were studied, and the following properties were discovered:

It is the last chemical element discovered in nature. It is one of the rarest, as it is very unstable and quickly disintegrates. According to scientists, the chemical element francium is present on Earth in only 30 grams. It can be classified as a liquid metal, but it is not liquid for long. After a few seconds, francium breaks down into more stable elements, in particular radium.

Application France

But, despite its high instability, this chemical element also brings benefits. It is used, although not widely. First of all, the chemical element francium is useful for detecting actinium in natural objects. In addition, thanks to experiments with laboratory rats, scientists have found that it accumulates in malignant tumors that are in the first stage of development. Therefore, it can be used for early diagnosis of sarcoma. But research into this element continues. Francius reveals more and more of his secrets to scientists.

Among the elements at the end of D.I. Mendeleev’s periodic table, there are those that non-specialists have heard and know a lot about, but there are also those that even a chemist can tell little about. The former include, for example, radon (No. 86) and radium (No. 88). The second is their neighbor in the periodic table, element No. 87 - France.

France is interesting for two reasons: firstly, it is the heaviest and most active alkali metal;

secondly, France can be considered the most unstable of the first hundred elements of the periodic table. France's longest-lived isotope, 223 Fr, has a half-life of only 22 minutes. Such a rare combination in one element of high chemical activity with low nuclear stability determined the difficulties in the discovery and study of this element.

How France was looking

Women scientists do not often have the joy of discovering new elements. Everyone knows the name of Marie Sklodowska-Curie, who discovered radium and polonium. Less well known is Ida Noddak (Tacke), who discovered rhenium. The discovery of element No. 87 is associated with the name of another woman - the Frenchwoman Marguerite Peret, by the way, a student of Marie Sklodowska-Curie. On January 9, 1939 she;

announced the discovery of element No. 87. Let us, however, go back almost 70 years and consider the history of the discovery of this element in more detail.

The possibility of existence and the basic properties of element No. 87 existed. 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 Physical-Chemical Society, he wrote: “Then in the tenth row one can expect more basic elements belonging to groups I, II and III . The first of them should form the oxide R2O, the second - RO, and the third - R2O3; 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, it would be expected that the metal itself would be liquid at room temperature, since cesium melts at 28 ° C. Due to its high reactivity, all terrestrial ecacesium should be found only in the form of salts, which, by their solubility, should be superior to the salts of other alkali metals, since when moving from lithium to cesium, the solubility of the salts increases. However, scientists of the 19th century failed to discover this interesting element.

After the discovery of element 87's radioactive neighbors, it became obvious that it too must be radioactive. But this did not clear up the situation.

Scientists who searched for the 87th element can be 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 the ashes of hay and mushrooms, in molasses and cigar ashes. 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 excasium in the waters 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 significant quantities of 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 these parts in July 1925, was interested in something else. “Already several years ago,” he wrote, “it occurred to me that if ekacesium was capable of permanent existence, then it could be found in the Dead Sea.”

All elements except alkaline ones were removed from water samples. Alkali metal chlorides were separated by fractional precipitation. Ekacesium chloride should have been the most soluble. However, the X-ray spectral analysis carried out at the last stage does not. made it possible to detect excasia.

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 excasium in X-ray diffraction patterns of manganese sulfate, and proposed the name “alkalinium” for the newly discovered element. In 1929, the American physicist F. Allison, using a fundamentally erroneous method of magneto-optical analysis, discovered traces of element 87 in rare alkali metal minerals - samarskite, pollucite and lepidolite. He named “his” element virginium. In 1931, American scientists J. Papish and E. Weiner even seemed to isolate excasium from the mineral samarskite, and in 1937, Romanian chemist G. Hulubey discovered excesium in the mineral pollucite and named it moldavium. But all these discoveries could not be confirmed, because the discoverers of alkalinium, Virginia and Moldova, did not in the least take into account the important property of excasium - its radioactivity.

However, failures also plagued the second group of scientists searching for the 87th element among the decay products of radioactive families. None of the radioactive families known at that time - uranium-238 (4 n+ 2), uranium-235 (4 n+ 3) and thorium-232 (4 n) - the lines of radioactive transformations did not pass through the isotopes of the 87th element. This could be for two reasons: either element No. 87 is a member of the missing row (4 n + 1),

or the process of radioactive decay of uranium-238 or uranium-235 in the radium-polonium section has not been thoroughly studied. Indeed, already 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 210 Tl, or beta decay, turning into the 214 Po isotope. This phenomenon is called branched decay or radioactive fork. One could expect the existence of similar forks in the radium-polonium area.

The first report of the discovery of element 87 as a product of radioactive decay appeared back in 1913 and belonged to the English chemist J. Cranston. Working with the 227 Ac preparation, he discovered the presence of weak alpha radiation in this isotope (in addition to the previously known beta radiation). As a result of the alpha decay of 227 Ac, it turns into the isotope of the 87th element - 224 87. Unfortunately, Cranston's message went unnoticed.

A year later, three Austrian radiochemists - Meyer, Hess and Paneth - observed the phenomenon of branched decay of the isotope 227 Ac, belonging to the uranium-235 series (4 n+ 3). They discovered alpha particles with a path length in air of 3.5 cm. “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, many treated the conclusions of these scientists with distrust. It was caused mainly 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 similar alpha particles.

Along with these experimental works, the theoretical research of the Odessa chemist D. Dobroserdov is of interest. In 1925, he published a message in the Ukrainian Chemical Journal in which he expressed interesting thoughts about the atomic weight, the physical and chemical properties of the 87th element, and where and by what methods one should look for it. In particular, he emphasized that excasium “must certainly be a very radioactive element.” However, Dobroserdov made an unfortunate mistake in assuming that the known radioactivity of potassium and rubidium was explained by the presence of excesium in them.

In the event of the discovery of an element with such interesting properties by Russian scientists, Dobroserdov intended to call it russium.

The following year, two works appeared at once: outstanding radiochemists O. Hahn (Germany) and D. Hevesy (Hungary) attempted to prove the presence of excasium in radioactive series. Hevesy 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 the beta decay of emanations, isotopes of the 87th element are not formed, and during the decay of actinium-228, if the isotope 224 is formed 87, then its quantity should be less than 1/200000 of the original number of 228 Ac cores.

12 years passed, and at the end of 1938, the French chemist Margarita Pere, an employee of the Paris Radium Institute, began searching for the 87th element. 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 were emitted by actinium and not protactinium, Pere very carefully purified the sea anemone from impurities and daughter products. By co-precipitation with tetravalent cerium hydroxide, she removed radioactinium, an isotope of thorium, from the solution; Isotopes of radium were derived with barium carbonate, and actinium 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, beta activity was clearly detected in the evaporation residue with a half-life of 22 minutes. It became clear that this activity was associated with some 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. The activity transferred to the precipitate along with cesium perchlorate. The activity of the resulting cesium perchlorate crystals 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, the emission of alpha particles produces a beta emitter with the properties of a heavy alkali metal and a half-life of 22 minutes:

The long and painstaking work was successful, and on September 9, 1939, Pere announced the discovery of element No. 87. In accordance with the nomenclature used for natural radioelements, she chose the name “actinium-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 it was studied

In addition to 223 Fr, several isotopes of element No. 87 are now known. But only 223 Fr exists in nature in any noticeable quantities. Using the law of radioactive decay, we can calculate that a gram of natural uranium contains 4-10 -18 grams of 223 Fr. This means that about 500 grams of France-223 are in radioactive equilibrium with the entire mass of earth’s uranium. There are two more isotopes of element No. 87 in vanishingly small quantities on Earth - 224 Fr (a member of the radioactive thorium family) and 221 Fr. Naturally, it is almost impossible to find an element on Earth whose global reserves do not reach a kilogram. Therefore, all studies on France and its few compounds have been performed 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 isolating this isotope using paper chromatography,

In this method, a solution of 227 Ac containing 223 Fr is applied to the end of a paper tape, which is immersed in the elution solution. When the solution moves along the paper tape, radioelements are distributed along it. 223 Fr, being an alkali metal, moves with the solvent front and is deposited later than other elements. Later, Adlov proposed using the complex organic compound a-thenoyltrifluoroacetone (TTA) to isolate 223 Fr. Using the described method, it is possible to isolate pure France-223 in 10-40 minutes. Due to its short half-life, you can work with this drug for no more than two hours, after which a noticeable amount of daughter products is formed and you need to either clear France of them or isolate it again.

With the development of ion acceleration technology and the creation of cyclotrons, new methods for producing France were developed. When thorium or uranium targets are irradiated with high-energy protons, France isotopes are formed. The longest-lived of them was francium-212 with a half-life of 19.3 minutes. In 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 grams of France-212 are formed with an activity of 2.5 10 7 decays per minute.

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

Another method of obtaining France is based on reactions that occur when targets made of lead, thallium or gold are irradiated with multiply charged ions of boron, carbon or neon, accelerated in cyclotrons or linear accelerators. The following target-projectile pairs are suitable: Pb + B; Tl+C; Au + Ne. For example, francium-212. is formed by irradiating gold foil with neon-22 ions with an energy of 140 MeV:

79 197 Au + 10 22 Ne = 89 219 Ac = 87 212 Fr + 2 4 He + 3 0 1 n

The most convenient and fastest method for isotope isolation from irradiated gold was developed by Soviet radiochemists N. Maltseva and M. Shalaevsky. France is extracted with nitrobenzene in the presence of tetraphenyl borate from a column filled with silica gel.

Using all these methods, 18 isotopes of France were obtained with mass numbers from 203 to 213 and from 218 to 224.

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

All experiments to study the chemical properties of francium were carried out, naturally, with ultra-small quantities of this element. The solutions contained only 10 -13 – 10 -9 grams of France. At such concentrations, processes that we usually forget about when dealing with macro quantities of a substance can become important. For example, under these conditions, a radioactive isotope can be “lost” from solution, adsorbed on the walls of vessels, on the surface of sediments, on possible impurities... Therefore, it would seem that 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 France with various insoluble compounds has been most fully studied. It is carried away from solution by cesium and rubidium chloroplatinates Cs2PtCl6 and Rb2PtCl6, chlorobismuthate Cs2BiCl6, chlorostannate Cs2SnCl6 and cesium chloroantimonate Cs2SbCl6 2.5H2O, as well as free heteropolyacids - silicon-tungstic and phosphotungstic.

France is easily adsorbed on ion exchange resins (sulfonic cation exchangers) from neutral and slightly acidic solutions. With the help of these resins it is easy to separate France from most chemical elements. That, perhaps, is all the success.

Of course, one cannot expect widespread use of element No. 87 in practice. And yet there are benefits from France. Firstly, with its help (by its radiation) you can quickly determine the presence of actinium in natural objects; Secondly, France hopes to use it for the early diagnosis of sarcomas. Preliminary experiments were carried out to study the behavior of France in the body of rats. It was found that France selectively accumulates in tumors, and in the early stages of the disease. These results are very interesting, but only the future will tell whether they will be able to be used in oncological practice.

They looked for the substance next to him.

We studied mainly minerals. Scientists thought several times that they had discovered metal.

At first, chemists in the American state of Virginia rejoiced, after which they wanted to name the element.

The initiative was seized by scientists from Moldova, who also decided that they had found francium. They “found” him in Russia, calling him a Russian.

But, as can be seen from the final title, the discovery of metal belongs to the French, more precisely, to one of them - Margarita Perey.

She worked at the Curie Institute in Paris, where she extracted francium from an anemone preparation.

Properties France

Actinium is another element of the periodic table, toxic, close to lanthanum. While studying a metal preparation, Margarita Perey discovered beta radiation that did not match any of the known isotopes.

It was 1939. Francium remained one of the 4 undiscovered substances. The half-life of the isotope discovered by Perey when purifying actinium from radioactive products was 21 minutes.

The isotope was subjected to research. The properties of the substance completely coincided with the predictions of Mendeleev, that is, with the parameters of eco-cesium. The research took almost 10 years. France was included in the table in 1946.

As is already clear, francium is an element of the periodic table with radioactive properties.

Because of them, the metal is examined in microscopic quantities so that the radiation does not exceed the norm.

Its chemical activity also requires caution when handling francium. Of the alkali metals, to which hero belongs, it is the highest.

Since the element is alkaline, it means that it is located in the main subgroup of the 1st group of the periodic table. Period seven.

The atomic number of francium is 87, and the mass is corresponding. The oxidation state of the metal is 1st, displayed as +1.

When the properties are similar to cesium, the standard potential of the 87th element is more negative.

This means that the substance can only be released at the mercury cathode. The study stops the instability of the amalgam France, that is, its connection with.

The duet breaks up in a matter of minutes, as soon as the current is turned off. So, many of the chemical properties of the most active of the alkali metals are proclaimed, so to speak, theoretically, based on calculations and not experiments.

Francium - element, inclined to form. Most of them are easily soluble in water.

Exceptions are: perchlorate, chloroplatinate, picrate cobaltinitrite. They are slightly soluble.

The 87th metal also comes into contact with heteropolyacids. The element is released along with them from acidic solutions.

Forms francium and halides. This is the name given to compounds of halogens located in the main subgroup of the 7th group of the periodic table with other elements.

Among the halides of the 87th metal there are volatile ones, for example, France chloride. Sublimation begins at 225 degrees in air and at 110 in a vacuum.

The melting point of francium is much lower - only 27 degrees. The substance boils at 667 Celsius.

The calculated density of the metal is 1.9 grams per cubic centimeter. At the same time, everything changes when the 87th element passes its half-life.

The result is the transformation of francium into an isotope of another metal - radium.

Application France

So far, francium is interesting to science only from a theoretical point of view. The substance is radioactive and decays quickly, making it difficult to work with.

In addition, francium cannot be obtained in large quantities, and most importantly, cannot be found in nature. That is why research related to minerals was not successful.

That is why Margarita Perey discovered francium in actinium preparations obtained artificially.

In general, the substance is not only dangerous, but also in short supply, so industrialists try not to resort to its “services.”

In the 20th century chemical element francium, more precisely, its chloride was used to detect cancerous tumors and treat them.

Mutated cells have impermeable membranes. Oxygen does not penetrate. Fermentation of glucose begins inside. Hence the burst of energy, allowing the tumor to grow uncontrollably.

Francium chloride has the ability to penetrate the membranes of cancer cells. The alkaline environment of the metal brings Ph to normal and blocks the fermentation of glucose.

Sounds good. But cesium chloride is also capable of this. Therefore, doctors stopped using scarce francium, although its effectiveness is slightly higher.

Extraction France

Margarita Perey once discovered an isotope of francium with a half-life of 21 minutes.

The most stable isotope of the element is not far away. Its half-life is 22.5 minutes.

This isotope can be found in the natural branches of the radioactive series of uranium 235.

Thorium also has a similar series. But, they find 224 francium in it with a half-life of only 3 minutes.

It turns out that there is, after all, Frenchium in the earth’s crust. Only now, its quantity is so small that it cannot be considered reserves.

The equilibrium content of the 224th isotope, for example, is only 0.5 grams.

Equilibrium is the relative mass content of a substance in the gas sphere. The total amount of francium in the earth's crust does not exceed 30 grams.

Francium is obtained, as in the 1940s, from actinium. It is impossible to isolate pure metal. Only compounds 87 are obtained from actinium element.

Characteristics France allows you to disconnect it using an ion exchange method. The separation is carried out on a column with Dauex-50 resin.

The purity of the extracted francium is 95%. Considering that the half-life of the most “tenacious” isotope is 22 minutes, after 11 of them the amount of metal is halved.

Since francium is similar in properties to cesium, it co-crystallizes with its compounds. Cesium has a number of insoluble compounds.

Francium is mined by coprecipitation with them. Most often, cesium perchlorate or silicotungstate is used.

Precipitation from solutions is carried out in special laboratories designed to work with radioactive substances.

Price France

In the case of metals, the price is usually set per gram. But France is an exception.

One gram of the 87th element is quantitatively comparable to tons of , , , if we focus on the content of metals in the earth’s crust.

Therefore, the cost of France is so high that it is not announced, and there is no need for it. As already mentioned, the substance has no practical use.

It is used for scientific and laboratory experiments. But French scientists can obtain the necessary micrograms themselves.

There is no need to purchase a reagent. Therefore, the price of a metal is as theoretical as many of its properties. One of them is the desire to dissolve oneself.

Francium is so radioactive and chemically mobile. Perhaps this is why there is so little substance... Has element 87 already dissolved most of its reserves?

When analyzing them, it is worth considering that francium is the heaviest of the alkali metals. For clarity, let’s imagine cotton wool.

To gain 30 grams, you need large volumes. To stock up on a similar amount of the 87th substance, grains are enough.