Cesium. Do you know how Geochemistry and Mineralogy

DEFINITION

Cesium located in the sixth period of group I of the main (A) subgroup of the Periodic table.

Belongs to the family s-elements. Metal. Designation - Cs. Serial number - 55. Relative atomic mass - 132.95 amu.

Electronic structure of the cesium atom

A cesium atom consists of a positively charged nucleus (+55), inside of which there are 55 protons and 78 neutrons, and 55 electrons move around in six orbits.

Fig.1. Schematic structure of the cesium atom.

The distribution of electrons among orbitals is as follows:

55Cs) 2) 8) 18) 18) 8) 1 ;

1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 2 5p 6 6s 1 .

The outer energy level of the cesium atom contains 1 electron, which is a valence electron. There is no excited state. The energy diagram of the ground state takes the following form:

The valence electron of a cesium 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

Cesium(lat. Caesium), Cs, chemical element of group I of the periodic system of Mendeleev; atomic number 55, atomic mass 132, 9054; silvery-white metal, belongs to the alkali metals. It occurs in nature as the stable isotope 133 Cs. Of the artificially produced radioactive isotopes with mass numbers from 113 to 148, the most stable is 137 Cs with a half-life T ½ = 33 years.

Historical reference. Cesium was discovered in 1860 by R. W. Bunsen and G. R. Kirchhoff in the waters of the Durkheim mineral spring (Germany) using the method of spectral analysis. It is named Cesium (from the Latin caesius - sky blue) for its two bright lines in the blue part of the spectrum. Metallic Cesium was first isolated by the Swedish chemist K. Setterberg in 1882 during the electrolysis of a molten mixture of CsCN and Ba.

Distribution of Cesium in nature. Cesium is a typical rare and trace element. The average content of Cesium in the earth's crust (clarke) is 3.7·10 -4% by mass. Ultramafic rocks contain 1·10 -5% Cesium, basic rocks contain 1·10 -4%. Cesium is geochemically closely related to granitic magma, forming concentrations in pegmatites together with Li, Be, Ta, Nb; especially in pegmatites rich in Na (albite) and Li (lepidolite). Two extremely rare Cesium minerals are known - pollucite and avogadrite (K,Cs)(BF) 4; the highest concentration of Cesium is in pollucite (26-32% Cs 2 O). Most of the Cesium atoms isomorphically replace K and Rb in feldspars and micas. Cesium impurity is found in beryl, carnallite, and volcanic glass. Weak enrichment of Cesium has been detected in some thermal waters. In general, Cesium is a weak aquatic migrant. The processes of isomorphism and sorption of large Cesium cations are of primary importance in the history of Cesium. Geochemically, Cesium is close to Rb and K, and partly to Ba.

Physical properties of Cesium. Cesium is a very soft metal; density 1.90 g/cm 3 (20 °C); t pl 28.5 °C; t boil 686 °C. At ordinary temperatures it crystallizes in a body-centered cubic lattice (a = 6.045 Å). Atomic radius 2.60 Å, ionic radius Cs + 1.86 Å. Specific heat capacity 0.218 kJ/(kg K); specific heat of fusion 15.742 kJ/kg (3.766 cal/g); specific heat of evaporation 610.28 kJ/kg (146.0 cal/g); temperature coefficient of linear expansion (0-26 °C) 9.7·10 -5; thermal conductivity coefficient (28.5°C) 18.42 W/(m K); electrical resistivity (20 °C) 0.2 μΩ m; temperature coefficient of electrical resistance (0-30°C) 0.005. Cesium is diamagnetic, specific magnetic susceptibility (18 °C) -0.1·10 -6. Dynamic viscosity 0.6299 Mn·s/m2 (43.4 °C), 0.4065 Mn·s/m2 (140.5 °C). Surface tension (62 °C) 6.75·10 -2 n/m (67.5 dynes/cm); compressibility (20 °C) 7.05 MN/m2 (70.5 kgf/cm2). Ionization energy 3.893 eV; standard electrode potential is 2.923 V, electron work function is 1.81 eV. Brinell hardness 0.15 Mn/m2 (0.015 kgf/cm2).

Chemical properties of Cesium. The configuration of the outer electrons of the Cesium atom is 6s 1; in compounds it has an oxidation state of + 1. Cesium has a very high reactivity. In air, it ignites instantly with the formation of peroxide Cs 2 O 2 and superoxide CsO 2; with a lack of air, Cs 2 O oxide is obtained; ozonide CsO 3 is also known. Cesium reacts explosively with water, halogens, carbon dioxide, sulfur, carbon tetrachloride, giving, respectively, hydroxide CsOH, halides, oxides, sulfides, CsCl. It interacts with hydrogen at 200-350 °C and a pressure of 5-10 Mn/m2 (50-100 kgf/cm2), forming a hydride. Above 300 °C, cesium destroys glass, quartz and other materials, and also causes corrosion of metals. When heated, cesium combines with phosphorus, silicon, and graphite. When Cesium interacts with alkali and alkaline earth metals, as well as with Hg, Au, Bi and Sb, alloys are formed; with acetylene - acetylenide Cs 2 C 2. Most simple Cesium salts, especially CsF, CsCl, Cs 2 CO 3, Cs 2 SO 4, CsH 2 PO 4, are highly soluble in water; CsMnO 4, CsClO 4 and Cs 2 Cr 2 O 7 are poorly soluble. Cesium is not a complex-forming element, but it is included in many complex compounds as an environmental cation.

Obtaining Cesium. Cesium is obtained directly from pollucite by vacuum-thermal reduction. Ca, Mg, Al and other metals are used as reducing agents.

Various cesium compounds are also obtained by processing pollucite. First, the ore is enriched (by flotation, manual mining, etc.), and then the separated concentrate is decomposed either with acids (H 2 SO 4, HNO 3 and others) or by sintering with oxide-salt mixtures (for example, CaO with CaCl 2). From the decomposition products of pollucite, cesium is precipitated in the form of CsAl(SO 4) 2 ·12H 2 O, Cs 3 and other poorly soluble compounds. Next, the sediments are converted into soluble salts (sulfate, chloride, iodide and others). The final stage of the technological cycle is the production of especially pure cesium compounds, for which methods of crystallization from solutions of Cs, Cs 3, Cs 2 and sorption of impurities on oxidized activated carbons are used. Deep purification of metallic Cesium is carried out using the rectification method. It is promising to obtain cesium from waste from the processing of nepheline, some mica, as well as groundwater during oil production; Cesium is extracted by extraction and sorption methods.

Cesium is stored either in Pyrex glass ampoules in an argon atmosphere, or in sealed steel vessels under a layer of anhydrous vaseline or paraffin oil.

Application of Cesium. Cesium is used for the manufacture of photocathodes (antimony-cesium, bismuth-cesium, oxygen-silver-cesium), electrovacuum photocells, photomultipliers, and electron-optical converters. Cesium isotopes are used: 133 Cs in quantum frequency standards, 137 Cs in radiology. The resonant frequency of the energy transition between sublevels of the ground state of 133 Cs forms the basis for the modern definition of the second.

Cesium in the body. Cesium is a permanent chemical microcomponent of the body of plants and animals. Seaweeds contain 0.01-0.1 mcg of Cesium per 1 g of dry matter, land plants - 0.05-0.2. Animals receive Cesium through water and food. In the body of arthropods there is about 0.067-0.503 μg/g of Cesium, in reptiles - 0.04, in mammals - 0.05. The main depot of Cesium in the body of mammals is muscles, heart, liver; in the blood - up to 2.8 mcg/l. Cesium is relatively low-toxic.

Cesium-137 (137 Cs) is a beta-gamma emitting radioisotope of Cesium; one of the main components of radioactive contamination of the biosphere. Contained in radioactive fallout, radioactive waste, discharges from factories processing waste from nuclear power plants. Intensively sorbed by soil and bottom sediments; in water it is found mainly in the form of ions. Contained in plants and the body of animals and humans. The accumulation rate of 137 Cs is highest in freshwater algae and arctic land plants, especially lichens. In the body of animals, 137 Cs accumulates mainly in the muscles and liver. The highest accumulation rate is observed in reindeer and northern American waterfowl. In the human body, l37 Cs is distributed relatively evenly and does not have any significant harmful effects.

DEFINITION

Cesium- the fifty-fifth element of the Periodic Table. Designation - Cs from the Latin "caesium". Located in the sixth period, IA group. Refers to metals. The core charge is 55.

Cesium occurs naturally in numerous minerals, the most important of which are pollucite (Cs,Na) 2 Al 2 Si 4 O 12 × H 2 O and avogadrite (K, Cs) BF 4. It is known that it is also included in some aluminosilicates as an impurity.

In the form of a simple substance, cesium is a golden-yellow metal (Fig. 1) with a body-centered crystal lattice. Density - 1.9 g/cm3. Melting point 28.4 o C, boiling point - 685 o C. Soft, easy to cut with a knife. Self-ignites in air.

Rice. 1. Cesium. Appearance.

Atomic and molecular mass of cesium

The relative molecular mass of a substance (M r) is a number showing how many times the mass of a given molecule is greater than 1/12 the mass of a carbon atom, and the relative atomic mass of an element (A r) is how many times the average mass of atoms of a chemical element is greater than 1/12 mass of a carbon atom.

Since cesium exists in the free state in the form of monatomic Cs molecules, the values ​​of its atomic and molecular masses coincide. They are equal to 132.9054.

Cesium isotopes

It is known that in nature cesium can be found in the form of the only stable isotope 133 Cs. The mass number is 133, the nucleus of an atom contains fifty-five protons and seventy-eight neutrons.

There are artificial unstable isotopes of cesium with mass numbers from 112 to 151, among which the longest-lived isotope 135 Cs with a half-life of 2.3 million years.

Cesium ions

At the outer energy level of the cesium atom there is one electron, which is a valence electron:

1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 2 5p 6 6s 1 .

As a result of chemical interaction, cesium gives up its valence electron, i.e. is its donor, and turns into a positively charged ion:

Cs 0 -1e → Cs + .

Cesium molecule and atom

In the free state, cesium exists in the form of monoatomic Cs molecules. Here are some properties characterizing the cesium atom and molecule:

Cesium alloys

Cesium is used in the form of alloys with antimony, calcium, barium, aluminum and silver as solar cells.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Cesium is part of a group of chemical elements with limited reserves, along with hafnium, tantalum, beryllium, rhenium, platinum group metals, cadmium, and tellurium. The total identified world ore resources are about 180 thousand tons (in terms of cesium oxide), but they are extremely dispersed. Super-high prices have been a constant feature of cesium and rubidium in the past and present. The global production of cesium is about 9 tons per year, and the demand is over 85 tons per year and is constantly growing. Cesium also has disadvantages that determine the constant search for its minerals: the extraction of this metal from ores is incomplete, during the operation of the material it dissipates and is therefore irretrievably lost, reserves of cesium ores are very limited and cannot meet the ever-growing demand for metal cesium (metal needs more than 8.5 times higher than its production, and the situation in cesium metallurgy is even more alarming than, for example, in the metallurgy of tantalum or rhenium). Industry needs very pure material (at the level of 99.9-99.999%), and this is one of the most difficult tasks in the metallurgy of rare elements. To obtain cesium of a sufficient degree of purity, repeated rectification in a vacuum, purification from mechanical impurities on metal-ceramic filters, heating with getters to remove traces of hydrogen, nitrogen, oxygen and repeated stepwise crystallization are required. Cesium is very active and aggressive towards container materials and requires storage, for example, in vessels made of special glass in an atmosphere of argon or hydrogen (cesium destroys conventional brands of laboratory glass).

Place of Birth

Canada is the leader in the production of cesium ore (pollucite). The Bernick Lake deposit (southeastern Manitoba) contains about 70% of the world's cesium reserves. Pollucite is also mined in Namibia and Zimbabwe. In Russia, its powerful deposits are located on the Kola Peninsula, in the Eastern Sayan and Transbaikalia. Pollucite deposits are also found in Kazakhstan, Mongolia and Italy (Elba Island), but they have small reserves and are not of great economic importance.

The annual production of cesium in the world is about 20 tons.

Geochemistry and Mineralogy

The average cesium content in the earth's crust is 3.7 g/t. There is a slight increase in cesium content from ultramafic rocks (0.1 g/t) to acidic rocks (5 g/t). The bulk of it in nature is in dispersed form and only a small part is contained in its own minerals. Constantly increased amounts of cesium are observed in sparrowite (1-4%), rodicite (about 5%), avogadrite and lepidolite (0.85%). In terms of crystal chemical properties, cesium is closest to rubidium, potassium and thallium. Cesium is found in higher quantities in potassium minerals. Cesium, like rubidium, tends to accumulate at later stages of magmatic processes, and its concentrations reach the highest values ​​in pegmatites. The average cesium content in granite pegmatites is about 0.01%, and in individual pegmatite veins containing pollucite it even reaches 0.4%, which is about 400 times higher than in granites. The highest concentrations of cesium are observed in rare metal-replaced microcline-albite pegmatites with spodumene. During the pneumatolithic-hydrothermal process, increased amounts of cesium are associated with massifs of greisenized alaskites and granites with quartz-beryl-wolframite veins, where it is present mainly in muscovites and feldspars. In the hypergenesis zone (under surface conditions), cesium accumulates in small quantities in clays, clayey rocks and soils containing clay minerals, sometimes in manganese hydroxides. The maximum cesium content is only 15 g/t. The role of clay minerals is reduced to sorption; cesium is drawn into the interpacket space as an absorbed base. Active migration of this element in waters is very limited. The main amount of cesium migrates “passively”, in clay particles of river waters. In seawater the concentration of cesium is approx. 0.5 µg/l. Among the cesium minerals proper, the most common are pollucite (Cs, Na) nH2O (22 - 36% Cs2O), cesium beryl (sparrowite) Be2CsAl2(Si6O18) and avogadrite (KCs)BF4. The last two minerals contain up to 7.5% cesium oxide.

Obtaining cesium

The main cesium minerals are pollucite and the very rare avogadrite (K,Cs). In addition, in the form of impurities, cesium is included in a number of aluminosilicates: lepidolite, phlogopite, biotite, amazonite, petalite, beryl, zinnwaldite, leucite, carnallite. Pollucite and lepidolite are used as industrial raw materials.
In industrial production, cesium in the form of compounds is extracted from the mineral pollucite. This is done by chloride or sulfate opening. The first involves treating the source mineral with heated hydrochloric acid, adding antimony chloride SbCl3 to precipitate the Cs3 compound, and washing with hot water or ammonia solution to form cesium chloride CsCl. In the second case, the mineral is treated with heated sulfuric acid to form cesium alum CsAl(SO4)2 · 12H2O.
In Russia, after the collapse of the USSR, industrial mining of pollucite was not carried out, although colossal reserves of the mineral were discovered in the Voronya tundra near Murmansk back in Soviet times. By the time the Russian industry was able to get back on its feet, it turned out that a Canadian company had bought the license to develop this field. Currently, the processing and extraction of cesium salts from pollucite is carried out in Novosibirsk at ZAO Rare Metals Plant.

There are several laboratory methods for obtaining cesium. It can be obtained:
heating in vacuum a mixture of cesium chromate or dichromate with zirconium;
decomposition of cesium azide in vacuum;
heating a mixture of cesium chloride and specially prepared calcium.

All methods are labor intensive. The second allows you to obtain high-purity metal, but is explosive and requires several days to implement.

Chemical properties

Cesium is the most chemically active metal, obtained in macroscopic quantities (since the activity of alkali metals increases with atomic number, francium is probably even more active, but is not obtained in macroscopic quantities, since all its isotopes have a short half-life). It is the strongest reducing agent. In air, cesium instantly oxidizes with combustion, forming superoxide CsO2. With limited access to oxygen, it is oxidized to Cs2O oxide. Interaction with water occurs explosively, the reaction product is hydroxide CsOH and hydrogen H2. Cesium reacts with ice (even at −120 °C), simple alcohols, organohalogen compounds, heavy metal halides, acids, dry ice (the interaction occurs with a strong explosion). Reacts with benzene. The activity of cesium is due not only to a high negative electrochemical potential, but also to a low melting and boiling point (a very large contact surface quickly develops, which increases the reaction rate). Many salts formed by cesium - nitrates, chlorides, bromides, fluorides, iodides, chromates, manganates, azides, cyanides, carbonates, etc. - are extremely easily soluble in water and a number of organic solvents; Perchlorates are the least soluble (which is important for the technology of cesium production and purification). Despite the fact that cesium is a very active metal, unlike lithium, it does not react with nitrogen under normal conditions and, unlike barium, calcium, magnesium and a number of other metals, it is not capable of forming compounds with nitrogen even at extreme heating.

Cesium hydroxide is the strongest base with the highest electrical conductivity in aqueous solution; for example, when working with it, it is necessary to take into account that a concentrated solution of CsOH destroys glass even at ordinary temperatures, and the melt destroys iron, cobalt, nickel, as well as platinum, corundum and zirconium dioxide, and even gradually destroys silver and gold (in the presence of oxygen - very quickly). The only metal stable in the cesium hydroxide melt is rhodium and some of its alloys.

It melts in your hands, but not snow - a riddle from the “chemistry” section. Guess – cesium. The melting point of this metal is 24.5 degrees Celsius. The substance, which literally flows through your fingers, was discovered in 1860. Cesium was the first element discovered by spectral analysis.

It was conducted by Robert Bunsen and Gustav Kirgoff. Chemists studied the waters of mineral springs in Durkheim. Found magnesium, lithium, calcium,... Finally, we placed a drop of water in the spectroscope and saw two blue lines - evidence of the presence of an unknown substance.

First, its chloroplatinate was isolated. For the sake of 50 grams, 300 tons of mineral water were processed. There was no trickery with the name of the new metal. From Latin “cesium” is translated as “blue”.

Chemical and physical properties of cesium

In a spectroscope, the metal glows bright blue. In reality, the element is similar to, but slightly lighter. In the liquid state, the yellowness of cesium disappears, and the melt becomes silvery. It is not easy to obtain raw materials for experiments.

Of the metals, the element is the rarest and most dispersed in the earth's crust. Only one isotope occurs in nature - cesium 133. It is completely stable, that is, it is not subject to radioactive decay.

Radioactive isotopes of the metal are obtained artificially. Cesium 135 is long-lived. Its half-life is approaching 3,000,000 years. Cesium 137 half decays in 33.5 years. The isotope is recognized as one of the main sources of biosphere pollution.

The nuclide enters it from discharges from factories and nuclear power plants. Half-life of cesium allows it to penetrate water, soil, plants, and accumulate in them. The 137th isotope is especially abundant in freshwater algae and lichens.

Being the rarest of the metals, cesium is also the most reactive. The alkaline element is located in the main subgroup of the 1st group of the periodic table, which already obliges the substance to easily enter into chemical reactions. Their flow is enhanced by the presence of water. Yes, in the air cesium atom explodes due to the presence of its vapors in the atmosphere.

Interaction with water is accompanied by an explosion, even if it is frozen. Reaction with ice is possible at -120 degrees Celsius. Dry ice is no exception. An explosion is also inevitable when cesium comes into contact with acids, simple alcohols, heavy metal halides, and organic halogens.

Interactions are easy to start for 2 reasons. The first is a strong negative electrochemical potential. That is, the atom is negatively charged and tends to attract other particles to itself.

The second reason is the surface area of ​​cesium during reactions with other substances. Melting in room conditions, the element spreads. It turns out that a larger number of atoms are open to interaction.

The activity of the element has led to the absence of its pure form in nature. There are only connections, for example, . Among them: cesium chloride, fluoride, iodite, azite, cyanite, bromide and cesium carbonate. All salts of the 55th element are easily soluble in water.

If work is carried out with cesium hydroxide, you need to be afraid not of its dissolution, but of the fact that it itself is capable of destroying, for example, glass. Its structure is disrupted by the reagent already at room temperature. As soon as you increase the degree, the hydroxide will not spare cobalt, corundum, and iron.

Reactions occur especially quickly in an oxygen environment. Only cesium hydroxide can resist. Nitrogen does not interact with element 55 either. Cesium asite is obtained only indirectly.

Applications of cesium

Cesium, formula which provides a low electron work function, is useful in the manufacture of solar cells. In devices based on the 55th substance, the cost of generating current is minimal. Sensitivity to radiation, on the contrary, is maximum.

To prevent photovoltaic equipment from being prohibitively expensive due to the rarity of cesium, it is alloyed with , , , . Cesium is used as a current source in fuel cells. Solid electrolyte based on 55 metal - part of cars and high-energy batteries.

The 55th metal is also used in charged particle counters. Cesium iodide is purchased for them. Activated with thallium, it detects almost any radiation. Cesium detectors are purchased for nuclear enterprises, geological exploration, and medical clinics.

They also use devices from the space industry. In particular, Mars-5 studied the elemental composition of the surface of the red planet thanks to a cesium-based gamma spectrometer.

The ability to capture infrared rays is the reason for its use in optics. They add to it cesium bromide And cesium oxide. It is found in binoculars, night vision goggles, and weapon sights. The latter are triggered even from space.

The 137th isotope of the element also found worthy use. The radioactive nuclide not only pollutes the atmosphere, but also sterilizes products, or rather, containers for them. Half-life of cesium long Millions of canned foods can be processed. Sometimes meat is also sterilized - bird carcasses and...

Medical instruments and medicines can also be processed with the 137th isotope. The nuclide is also needed in the treatment itself when it comes to tumors. The method is called radiotherapy. Preparations with cesium are also given for schizophrenia, diphtheria, peptic ulcers, and some types of shock.

Metallurgists need a pure element. It is mixed with alloys and. The additive increases their heat resistance. In , for example, it triples with cesium at only 0.3%.

Tensile strength and corrosion resistance also increase. True, industrialists are looking for an alternative to the 55th element. It is too scarce and not competitive in price.

Cesium mining

The metal is isolated from pollucite. It is a hydrous aluminosilicate and cesium. Minerals containing the 55th element of the unit. In pollucite, the percentage of cesium makes mining economically feasible. There is also a lot of metal in avogardite. However, this stone itself is as rare as cesium.

Industrialists open pollucite with chlorides or sulfates. Cesium extracted from the stone by immersing it in heated hydrochloric acid. Antimony chloride is also poured there. A precipitate forms.

It is washed with hot water. The result of the operations is cesium chloride. When working with sulfate, pollucite is immersed in sulfuric acid. The output is cesium alum.

Laboratories use other methods for obtaining the 55th element. There are 3 of them, all labor intensive. You can heat cesium dichromate and zirconium chromate. But this requires a vacuum. It is also needed for the decomposition of cesium azide. Vacuum is avoided only by heating specially prepared calcium and chloride of the 55th metal.

Cesium price

In Russia, the Rare Metals Plant in Novosibirsk is engaged in the mining and processing of pollucite. The Lovozersk Mining and Processing Plant also offers products. The latter offers cesium in ampoules 10 and 15 milligrams.

They come in packs of 1000 pieces. Minimum price – 6000 rubles. Sevredmet also sells ampoules, but is ready to supply smaller volumes - from 250 grams.

If the purity of the metal is 99.9%, for one gram, as a rule, they ask for around 15-20 US dollars. We are talking about the stable 133rd isotope of the 55th element of the periodic table.