Atomic number of francium. Franc. Physical and chemical properties
| France | |
|---|---|
| Atomic number | 87 |
| Appearance simple substance | radioactive alkali metal |
| Properties of the atom | |
|
Atomic mass (molar mass) |
223.0197 a. e.m. (/mol) |
| Atomic radius | n/a pm |
| Ionization energy (first electron) |
380 kJ/mol (eV) |
| Electronic configuration | 7s 1 |
| Chemical properties | |
| Covalent radius | n/a pm |
| Ion radius | (+1e) 180 pm |
| Electronegativity (according to Pauling) |
0,7 |
| Electrode potential | Fr←Fr + −2.92 V |
| Oxidation states | +1 |
| Thermodynamic properties of a simple substance | |
| Density | 1.87 /cm³ |
| Molar heat capacity | n/a J/(mol) |
| Thermal conductivity | n/a W/(m) |
| Melting temperature | 300 |
| Heat of Melting | ~ 2 kJ/mol |
| Boiling temperature | 950 |
| Heat of vaporization | ~ 65 kJ/mol |
| Molar volume | n/a cm³/mol |
| Crystal lattice of a simple substance | |
| Lattice structure | cubic body-centered |
| Lattice parameters | n/a Å |
| c/a ratio | n/a |
| Debye temperature | n/a K |
| Fr | 87 |
| 7s 1 | |
| France | |
France- element of the main subgroup of the first group of the seventh period periodic table chemical elements D. I. Mendeleev, with atomic number 87. Denoted by the symbol Fr(Francium). Simple substance France(CAS number: 7440-73-5) is a radioactive alkali metal with high chemical activity.
History of discovery France
Francium 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.
Finding France in nature
Francium-223 (the longest-lived of the French isotopes, half-life 22.3 minutes) is found in one of the radioactive branches of the uranium-235 series and can be isolated from natural uranium minerals. Formed during the alpha decay of actinium-227:
227 Ac → 223 Fr (accompanied by α-radiation, decay probability approximately 1.4%),
227 Ac → 227 Th (accompanied by β-radiation, decay probability is about 98.6%).
Its old name is “sea anemone K” (AcK). It is estimated that its equilibrium content in earth's crust equals 340 g.
In addition, in one of the side branches of the radioactive series thorium contains francium-224 with a half-life of 3.0 minutes. Its equilibrium content in the earth's crust is only 0.5 g.
Receiving France
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.
Physical, chemical properties France
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, melting point 27°C, boiling point 677°C, specific heat of fusion 9.385 kJ/kg.
Application France
Salt France FrCl used to detect cancerous tumors, but due to the extreme high cost It is not profitable to use this salt in large-scale developments.
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.
Francium is one of the four elements of Mendeleev’s periodic table that were discovered “last of all.” Indeed, by 1925, all cells of the table of elements were filled in, with the exception of 43, 61, 85 and 87. Numerous attempts to discover these missing elements remained unsuccessful for a long time. Element 87 (Mendeleev's eka-cesium) was sought mainly in cesium minerals, hoping to find it as a satellite of cesium. In 1929, Allison and Murphy reported their discovery of ecaesium in the mineral lepidolite; They named the new element virginium in honor of the US state - Allison's homeland. In 1939, Khulubei discovered element 87 in pollux and named it moldavium. Other authors also reported the discovery of eka-caesium 87, and the collection of its names was enriched with alkalinium and russium. However, all these discoveries were wrong. In 1939, Perey from the Curie Institute in Paris was engaged in the purification of a preparation of actinium (Ac-227) from various radioactive decay products. Carrying out carefully controlled operations, she discovered beta radiation, which could not belong to any of the isotopes of the actinium decay series known at that time. However, a more in-depth study of the decay of actinium showed that the decay occurs not only along the main chain Ac-RaAc-AcX, but also along the side chain Ac-AcK-AcX with the formation of an unknown isotope with a half-life of 21 minutes. The isotope received the temporary designation AsK. When it was subjected to chemical research, it turned out that its properties corresponded to those of ec-cesium. After the Second World War, which interrupted Perey's work, her findings were fully confirmed. In 1946, Perey proposed to name element 87 francium in honor of her homeland, and the designation AcK remained for the corresponding isotope in the radioactive decay series of actinium. For some time it was believed that francium is formed only during the alpha decay of actinium. However, after neptunium was discovered and its radioactive decay series was studied, the formation of the isotope francium-221 with a half-life of 5 minutes was proven. during the alpha decay of the actinium-225 isotope. Francium, like astatine, is a very rare element; originally it had the symbol not Fr, but Fa.
(Francium; from the name of France), Fr - radioactive chemical. element of group I of the periodic system of elements; at. n. 87. It has no stable isotopes. 18 radioactive isotopes with mass numbers from 204 to 224 and half-lives from 5 10 -3 sec (218Fr) to 23 min (212Fr) were obtained. The existence of F. and some of his saints was predicted (1870) by a Russian. scientist D.I. Mendeleev, calling the element unknown at the time ecacesium. Ekacesium was discovered in 1939 in France. researcher M. Perey while studying the radioactive decay of actinium and called “actinium K”. In 1949, “actinium K” was renamed francium. The isotopes 223Fr and 221Fr are found in nature, of which the isotope 223Fr is a product of the radioactive decay of actinium 227Ac. 1m of natural uranium contains 0.2 mg of 227Ac and 3.8 10 -10 g of 223Fr. Francium is the heaviest element among the alkali metals. Atomic radius 12.83 A. Ionic radius Fr+ is 1.80 A. Density (temperature 20° C) 2.44 g/cm3; melting point 20° C; t boil 630° C; heat capacity 0.0338 cal/g-deg; electrical resistance (temperature 18 C) 45 10-6 ohm-cm.
According to chemistry Holy francium is a complete analogue of rubidium and cesium. Fluoride hydroxide, chloride, nitrate, sulfate, sulfide, carbonate, acetate and F. oxalate are highly soluble in water; perchlorate, picrate, iodate, chloroplatinate, chlorobismuthate, chloro-antimonate, chlorostannate and cobaltinitrite F., as well as the double salt Fr9Bi2I9 and francium salts with heteropolyacids are poorly soluble in water. Francium is isolated by various methods from the decay products of 227Ac, from uranium resin ore, from the products of irradiation of thorium and uranium with fast protons, as well as from the products of irradiation of gold with 22Ne ions. When isolating phosphorus from the decomposition products of 227Ac, an aqueous solution of actinium chloride is boiled with an excess of sodium carbonate, the precipitate is filtered off, hydrochloric acid is added to the filtrate and boiled again to destroy carbonate ions. Then small amounts of lanthanum and barium chloride, potassium and ammonium chromate are added. After this, the chromate precipitate is filtered off, and the filtrate containing 223Fr is concentrated by evaporation. To isolate francium from solutions containing, in addition to phosphorus salts, other compounds, ion-exchange resins, methods of electrophoresis, chromatography, etc. are used. With the help of francium, the presence of actinium in natural objects is determined. The 223Fr isotope is used in biological research.
Element characteristics
One thing is certain - its valence electron is located at 7s -orbitals, and the atomic radius is the largest among all elements of the periodic table. Francium is a radioactive chemical element. It has no stable isotopes, and those that are known are short-lived and quickly decay, emittingβ -radiation (electrons). There is barely ~500g of it on the entire globe.
Properties of simple matter and compounds
All data on the properties of francium were obtained by extrapolation based on results of co-precipitation with other elements. Chemically, Ig is the closest analogue of cesium, while francium is even more electropositive. Its only stable oxidation state is +1.
Receipt and use
Francium is obtained only in the form of its compound by separation from actinium. Using ion exchange separation on a resin column« Dowex-50" a microscopic amount of 95% pure francium can be obtained. However, its half-life is 22 minutes, i.e., after each such interval its amount is halved. It has not found any application yet. Radio emission from France helps to find. Publications have appeared claiming that the radioactivity of francium may be useful in diagnosing cancer: it is selectively capable of accumulating in tumors at the most early stages their development.
You are reading an article on the topic of France
Francium is an element with atomic number 87. The atomic mass of the longest-lived isotope is 223. Francium is a radioactive alkali metal and has extremely pronounced chemical reactivity.
FranciumHistory of the discovery of France
The metal was discovered back in 1939 by an employee of the Paris Radium Institute named Margarita Perey. She, apparently out of patriotic feelings, named the element in honor of her Motherland. Francium was discovered during the study of the artificially produced element “actinium”: an uncharacteristic radioactive glow was noticed. To be fair, it should be noted that other researchers could have worked simultaneously with her on the creation of this element, but, as they say, the winners are not judged.
Main characteristics
Today, francium is one of the rarest metals (and chemical elements in general) found in nature.
Earth's Crust
According to scientists' calculations, the content of this metal in the earth's crust is about 340 grams (only astatine contains less). This is mainly due to his physical instability. Being radioactive, it has a very short half-life (the most stable isotope has 22.3 minutes). The only thing that compensates for its natural content is the fact that francium is an intermediate in the decay of uranium-235 and thorium-232. Thus, all francium found naturally is a product of radioactive decay.
How can I get it?
Let's consider the only way to obtain the most stable isotope, francium. This can be done by nuclear reaction gold with oxygen atoms. All other methods (meaning radioactive decay) are impractical, since they produce extremely unstable isotopes that “live” no more than a few minutes. Obviously, you won’t be able to obtain this element, like all its compounds, at home (and there’s no reason to, actually). one can find many experiments with other metals.
What chemical properties does francium exhibit?
The properties of francium are similar to cesium. The relativistic effects of the 6p shell ensure that the bond between francium and oxygen in superoxides (for example, the composition FrO 2) is more covalent relative to the superoxides of other elements of this group. Taking into account the lowest electronegativity of all currently existing francs, it is characterized by pronounced chemical activity. All physical properties of this element are indicated only theoretically, since it is not possible to test them in practice due to the short “life” period of this element (density = 1.87 g/cm³, melting t = 27 °C, boiling t = 677 °C , specific heat of fusion=9.385 kJ/kg). All compounds of this element are soluble in water (exceptions: salts perchlorate, chloroplatinate, picrate cobaltinitrite francium). Francium always co-crystallizes with substances that contain cesium. Co-precipitation with insoluble cesium salts (cesium perchlorate or cesium silicotungstate) is observed. Extraction of francium from solutions is carried out:
- cesium and rubidium chloroplatinates Cs 2 PtCl 6 and Rb 2 PtCl 6 ;
- chlorobismuthate Cs 2 BiCl 5 , chlorostanate Cs 2 SnCl 6 and cesium chloroantimonate Cs 2 SbCl 5 2.5H 2 O;
- free heteropolyacids: silicotungstic and phosphotungstic.
What practical significance does this element have?
Despite all its uniqueness, France has not yet been used in practice. Accordingly, it is not used in industry or any technology. The reason for this is its extremely short half-life. There is evidence that francium chloride can be used to diagnose oncological tumors, however, due to the significant cost of this formation, this kind of technique cannot be introduced into systematic use. In principle, cesium has the same properties.
Caesium
So this property of franc also turned out to be unclaimed: its cost is compared with the cost of a ton of platinum or gold. According to leading experts, the element in question will always have purely cognitive value, nothing more.
