Strontium general characteristics. Strontium - characteristics of properties with a photo, its biological role in the human body, treatment with drugs based on a chemical element

Strontium(lat. Strontium), Sr, a chemical element of group II of the Mendeleev periodic system, atomic number 38, atomic mass 87.62, silver-white metal. Natural Strontium consists of a mixture of four stable isotopes: 84 Sr, 86 Sr, 87 Sr and 88 Sr; the most common is 88 Sr (82.56%).

Radioactive isotopes with mass numbers from 80 to 97 have been artificially obtained, incl. 90 Sr (T ½ = 27.7 years), formed during the fission of uranium. In 1790, the Scottish doctor A. Crawford, examining a mineral found near the settlement of Stronshian (in Scotland), discovered that it contains a previously unknown "earth", which was called strontian. It later turned out to be strontium oxide SrO. In 1808, G. Davy, subjecting to electrolysis with a mercury cathode a mixture of moistened Sr(OH) 2 hydroxide with mercury oxide, obtained Strontium amalgam.

Distribution of Strontium in nature. The average content of Strontium in the earth's crust (clarke) is 3.4·10 -2% by mass; in geochemical processes, it is a satellite of calcium. About 30 Strontium minerals are known; the most important are celestine SrSO 4 and strontianite SrCO 3 . In igneous rocks, strontium is predominantly in a dispersed form and enters as an isomorphic impurity into the crystal lattice of calcium, potassium, and barium minerals. In the biosphere, Strontium accumulates in carbonate rocks and especially in the sediments of salt lakes and lagoons (celestine deposits).

Physical properties of strontium. At room temperature, the lattice of Strontium is face-centered cubic (α-Sr) with a period a = 6.0848Å; at temperatures above 248 °C, it transforms into a hexagonal modification (β-Sr) with lattice periods a = 4.32 Å and c = 7.06 Å; at 614 °C it transforms into a cubic body-centered modification (γ-Sr) with a period a = 4.85Å. Atomic radius 2.15Å, ionic radius Sr 2+ 1.20Å. The density of the α-form is 2.63 g / cm 3 (20 ° C); t pl 770 °C, t kip 1383 °C; specific heat capacity 737.4 kJ/(kg K); electrical resistivity 22.76·10 -6 ohm·cm -1 . Strontium is paramagnetic, the atomic magnetic susceptibility at room temperature is 91.2·10 -6 . Strontium is a soft ductile metal that can be easily cut with a knife.

Chemical properties. The configuration of the outer electron shell of the atom Sr 5s 2 ; in compounds it usually has an oxidation state of +2. Strontium is an alkaline earth metal, chemically similar to Ca and Ba. Strontium metal rapidly oxidizes in air, forming a yellowish surface film containing SrO oxide, SrO 2 peroxide and Sr 3 N 2 nitride. With oxygen, under normal conditions, it forms SrO oxide (grayish-white powder), which readily transforms into carbonate SrCO 3 in air; interacts vigorously with water, forming hydroxide Sr (OH) 2 - a base stronger than Ca (OH) 2. When heated in air, it ignites easily, and powdered Strontium ignites spontaneously in air, so Strontium is stored in hermetically sealed vessels under a layer of kerosene. Rapidly decomposes water with the release of hydrogen and the formation of hydroxide. At elevated temperatures, it reacts with hydrogen (>200 °C), nitrogen (>400 °C), phosphorus, sulfur and halogens. When heated, it forms intermetallic compounds with metals, such as SrPb 3 , SrAg 4 , SrHg 8 , SrHg 12 . Of the strontium salts, the halides (except for fluoride), nitrate, acetate, and chlorate are readily soluble in water; hardly soluble carbonate, sulfate, oxalate and phosphate. Precipitation of Strontium as oxalate and sulfate is used for its analytical determination. Many Strontium salts form crystalline hydrates containing from 1 to 6 molecules of water of crystallization. SrS sulfide is gradually hydrolyzed by water; Sr 3 N 2 nitride (black crystals) is easily decomposed by water releasing NH 3 and Sr(OH) 2 . Strontium dissolves well in liquid ammonia, giving dark blue solutions.

Getting Strontium. The main raw materials for the production of strontium compounds are concentrates from the enrichment of celestine and strontianite. Strontium metal is obtained by reducing strontium oxide with aluminum at 1100-1150 °C:

4SrO+ 2Al = 3Sr+ SrO Al 2 O 3 .

The process is carried out in electrovacuum apparatuses [at 1 N/m 2 (10 -2 mm Hg)] of periodic action. Vapors of strontium condense on the cooled surface of a condenser inserted into the apparatus; at the end of the reduction, the apparatus is filled with argon and the condensate is melted, which flows into the mold. Strontium is also obtained by electrolysis of a melt containing 85% SrCl 2 and 15% KCl, however, in this process, the current efficiency is low, and the metal is contaminated with salts, nitride, and oxide. In industry, electrolysis with a liquid cathode produces strontium alloys, for example, with tin.

Application of Strontium. Strontium serves to deoxidize copper and bronze. 90 Sr is a source of β-radiation in atomic electric batteries. Strontium is used to make phosphors and solar cells, as well as highly pyrophoric alloys. Strontium oxide is a component of some optical glasses and oxide cathodes of vacuum tubes. Strontium compounds give flames an intense cherry red color, which is why some of them are used in pyrotechnics. Strontianite is introduced into the slag to clean high-grade steels from sulfur and phosphorus; Strontium carbonate is used in non-evaporative getters and is also added to weather-resistant glazes and enamels for coating porcelain, steels, and heat-resistant alloys. Chromate SrCrO 4 is a very stable pigment for the manufacture of artistic paints, SrTiO 3 titanate is used as a ferroelectric, it is part of piezoceramics. Strontium salts of fatty acids ("strontium soaps") are used to make special greases.

Salts and compounds of Strontium have low toxicity; when working with them, one should be guided by the safety regulations with salts of alkali and alkaline earth metals.

Strontium in the body. Strontium is an integral part of microorganisms, plants and animals. In marine radiolarians (acantaria), the skeleton consists of strontium sulfate - celestine. Seaweed contains 26-140 mg of Strontium per 100 g of dry matter, terrestrial plants - 2.6, marine animals - 2-50, terrestrial animals - 1.4, bacteria - 0.27-30. Accumulation of Strontium by various organisms depends not only on their species, characteristics, but also on the ratio of Strontium with other elements, mainly Ca and P, in the environment, as well as on the adaptation of organisms to a specific geochemical environment.

Animals receive Strontium with water and food. Strontium is absorbed by the thin, and excreted mainly by the large intestine. A number of substances (algae polysaccharides, cation exchange resins) prevent the absorption of Strontium. The main depot of Strontium in the body is bone tissue, the ashes of which contain about 0.02% Strontium (in other tissues - about 0.0005%). An excess of strontium salts in the diet of rats causes "strontium" rickets. In animals living on soils with a significant amount of celestine, there is an increased content of Strontium in the body, which leads to brittle bones, rickets and other diseases. In biogeochemical provinces rich in Strontium (a number of regions of Central and East Asia, Northern Europe, and others), the so-called Urov disease is possible.

Strontium-90. Among the artificial isotopes of Strontium, its long-lived radionuclide 90 Sr is one of the important components of radioactive contamination of the biosphere. Once in the environment, 90 Sr is characterized by the ability to be included (mainly together with Ca) in the metabolic processes of plants, animals, and humans. Therefore, when assessing the pollution of the biosphere with 90 Sr, it is customary to calculate the ratio of 90 Sr/Ca in strontium units (1 s.u. = 1 micron μcurie 90 Sr per 1 g Ca). When 90 Sr and Ca move along biological and food chains, Strontium discrimination occurs, for the quantitative expression of which the “discrimination coefficient” is found, the ratio of 90 Sr / Ca in the next link of the biological or food chain to the same value in the previous link. In the final link of the food chain, the concentration of 90 Sr, as a rule, is much lower than in the initial one.

Plants can receive 90 Sr directly from direct contamination of the leaves or from the soil through the roots (in this case, the type of soil, its moisture content, pH, content of Ca and organic matter, etc. have a great influence). Relatively more 90 Sr is accumulated by leguminous plants, root and tuber crops, less by cereals, including cereals, and flax. Significantly less 90 Sr is accumulated in seeds and fruits than in other organs (for example, 90 Sr is 10 times more in wheat leaves and stems than in grain). In animals (comes mainly with plant foods) and humans (comes mainly with cow's milk and fish), 90 Sr accumulates mainly in the bones. The amount of 90 Sr deposition in the body of animals and humans depends on the age of the individual, the amount of incoming radionuclide, the rate of growth of new bone tissue, and others. 90 Sr poses a great danger to children, in whose body it enters with milk and accumulates in rapidly growing bone tissue.

The biological effect of 90 Sr is related to the nature of its distribution in the body (accumulation in the skeleton) and depends on the dose of β-irradiation created by it and its daughter radioisotope 90 Y. With prolonged intake of 90 Sr into the body, even in relatively small quantities, as a result of continuous irradiation bone tissue, leukemia and bone cancer can develop. Significant changes in bone tissue are observed when the content of 90 Sr in the diet is about 1 microcurie per 1 g of Ca. The conclusion in 1963 in Moscow of the Treaty on the Ban on Tests of Nuclear Weapons in the Atmosphere, Outer Space and Under Water led to the almost complete release of the atmosphere from 90 Sr and a decrease in its mobile forms in the soil.

Atom number 38 with mass 87.62. It occurs in nature in a stable state in the form of 4 isotopes: 84, 86, 87, 88. The most common in nature is 88. Due to the decay of natural rubidium 87, the exact amount of strontium changes over time. Man received radioactive atoms with numbers 80-97.

Moreover, the most commonly used isotope was obtained from uranium - Strontium 90. The history of the discovery of the element goes back to the distant 90s of the eighteenth century. As early as 1787, strontium was first isolated from the mineral strontianite near the village of Strontiana in Scotland.

The first studies were carried out by chemists Ader Crawford and Martin Heinrich Klapot. In Russia, studies of strontium earth were carried out by Tobias Lovitz. A distinctive characteristic was burning with a bright red flame.

Description and properties of strontium

Strontium formula– Sr. It is a polymorphic white metal with a silvery sheen. Due to the rapid reaction in its pure form with atmospheric oxygen, it acquires an oxide film with a yellow tint. Strontium metal very soft and easy to forge.

It is presented in three modifications: cubic face-centered crystal lattice - up to 231 °C, hexagonal - from 231 to 623 °C, cubic body-centered - at temperatures above 623 °C. Strontium atom has the structure of the outer electron shell 5s2. In reactions, it is oxidized and takes the form +2, sometimes +1. Structure atom strontium: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s2

Main physical indicators:

Atomic volume - 34 cm 3 / g × atom;

The radius of the atom is 2.15 A;

Density - 2.63 g / cm 3 at 20 ° C;

Tm. = 770 °С;

Tbp. = 1380 °С;

Oud. heat 0.176 cal / g × deg at 20 ° C;

Vapor pressure 10-3 mmHg at 462°C, 1 mmHg 733°C and 100 mmHg at 1092°C;

Surface tension 165 dynes/cm;

Brinell hardness 13 kg/mm2;

Chemical characteristic of strontium. In terms of reactivity, strontium is close to its brothers in the barium and calcium groups. Under normal conditions, it quickly interacts with atmospheric oxygen. Formed strontium oxide SrO and SrO 2 with a yellowish tint.

Like all alkaline earth metals, it reacts with water to form strontium hydroxide. The interaction with halogens is very active - halides are formed. The powdered form of the metal ignites very quickly even at room temperature and atmospheric pressure.

Particularly important are iodide and strontium chloride. When heated, it actively combines with carbon dioxide, forming carbonate and bicarbonate. In the gas phase, the addition of hydrogen results in the formation of SrH 2 hydride. The following compounds are also most common: carbide - carbon-based compounds (SrC 2), amide - with ammonia in a gaseous state (Sr (NH 2) 2), sulfide - with sulfur (SrS), selenide - with selenium (SrSe) and some other.

Strontium in the molten state mixes easily with metals such as aluminium, iron, barium, and others. The melt is homogenized to obtain intermetallic compounds. Strontium reacts easily with dilute acids. A huge number of various salts are obtained in reactions with organic and mineral acids.

However, showing high reactivity with weak acids, with concentrated ones, on the contrary, it does not show activity. Therefore sulfates, nitrates, nitrites and others strontium salts obtained by reaction with dilute acids. The bulk of the salts are colored white with varying degrees of solubility in water (based on mineral acids, as a rule, dissolve better).

Characteristics of strontium as a radioactive element. A radioactive isotope is obtained in nuclear reactors during the β-decay of rubidium 90, after which strontium goes through the β-decay stage to produce yttrium nuclide 90. Half life of strontium equals 28.79 years.

Deposits and mining of strontium

Strontium is widely distributed in nature. The element in the form of ores lies in the earth's crust. More than 24% of the total supply of the element is in the world's oceans. Natural reserves exist only in a bound state and are minerals, the total number of which is at least 40. In the land of the CIS countries, Western Europe, North America, mainly in Canada, the largest deposits of ore were found: strontianite - strontium carbonate and - strontium sulfate.

Industrial methods for obtaining metal are based on the processing of mineral ores with various compounds. After that, the thermal decomposition of the compounds, or electrolytic action, is carried out. However, as a result of such reactions, a powdered form of the metal is formed, which is very flammable, or the yield of the element is very low and is obtained with impurities. Therefore, the methods described above are not currently used.

The most popular is the reduction of strontium oxide with the addition of metallic aluminum and flint sand. The reaction takes place in a vacuum tube made of steel at very high temperatures above 1,000 °C. The element is cleaned by distillation also under vacuum. For nuclear energy, it is extremely important to obtain radioactive isotopes.

They are produced in reactors during the half-life of Uranium 235. The isotope Sr 89 ( half-life of strontium 50.5 days) is formed after decay with the release of a huge amount of energy from a stable isotope. Strontium is an indispensable part of the animal and plant world. Many organisms accumulate the element in themselves together with calcium and phosphorus.

Application of strontium

In the form of a metal, it is used as an alloying agent. Adds malleability and ductility. Explosive when mixed with barium and calcium. It is part of thermite mixtures.

Use of strontium compounds:

SrO is part of oxide cathodes, pyrotechnic mixtures.

SrCO 3 - receive special coatings - chemically stable and heat-resistant glazes.

Sr(NO 3) 2 is a component of pyrotechnic substances for signal rockets.

SrSO 4 - filler for paints and rubber.

SrCrO 4 is a component of varnishes and primers in the aircraft industry.

SrTiO 3 is a material for the production of dielectric antennas, conductors and sensors.

SrF 2 - used in the production of specialized.

SrCl 2 is a component of pyrotechnic compositions, cosmetics and medical preparations.

SrS is used in the production of additives in the manufacture of leather.

90 Strontium 137 cesium is used as a component of radioactive fuel.

The most useful substance based on organic compounds - strontium ranelate- a bone growth stimulator. This drug is used to treat osteoporosis.

Strontium price

Strontium metal is most often sold in the form of compounds. Prices on strontium compounds varies widely: Nitrate - 3.8 USD, Chloride - 500-800 rubles, Ranelat in the form of preparations from 1500 to 2500 rubles.

DEFINITION

Strontium is the thirty-eighth element of the Periodic Table. Designation - Sr from the Latin "strontium". Located in the fifth period, IIA group. Refers to metals. The core charge is 38.

Strontium occurs in nature mainly as sulfates and carbonates, forming the minerals celestite SrSO 4 and strontianite SrCO 3 . The content of strontium in the earth's crust is 0.04% (mass.).

Metallic strontium in the form of a simple substance is a soft silvery-white (Fig. 1) metal with malleability and plasticity (it is easily cut with a knife). Reactive: oxidizes rapidly in air, interacts quite vigorously with water, and combines directly with many elements.

Rice. 1. Strontium. Appearance.

Atomic and molecular weight of strontium

DEFINITION

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

Since strontium exists in the free state in the form of monatomic Sr molecules, the values ​​of its atomic and molecular masses coincide. They are equal to 87.62.

Allotropy and allotropic modifications of strontium

Strontium exists in the form of three crystalline modifications, each of which is stable in a certain temperature range. So, up to 215 o C, α-strontium is stable (face-centered cubic lattice), above 605 o C - g - strontium (body-centered cubic lattice), and in the temperature range 215 - 605 o C - b-strontium (hexagonal lattice).

Isotopes of strontium

It is known that in nature rubidium can be in the form of the only stable isotope 90 Sr. The mass number is 90, the atomic nucleus contains thirty-eight protons and fifty-two neutrons. Radioactive.

Strontium ions

At the outer energy level of the strontium atom, there are two electrons that are valence:

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

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

Sr 0 -2e → Sr 2+ .

Molecule and atom of strontium

In the free state, strontium exists in the form of monatomic Sr molecules. Here are some properties that characterize the atom and molecule of strontium:

Strontium alloys

Strontium has found wide application in metallurgy as an alloying component of copper-based alloys.

Examples of problem solving

EXAMPLE 1

Strontium- an element of the main subgroup of the second group, the fifth period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 38. It is denoted by the symbol Sr (lat. Strontium). The simple substance strontium is a soft, malleable and ductile alkaline earth metal of a silvery-white color. It has a high chemical activity, in air it quickly reacts with moisture and oxygen, becoming covered with a yellow oxide film.

In 1764, a mineral was found in a lead mine near the Scottish village of Strontian, which they called strontianite. For a long time it was considered a variety of fluorite CaF2 or witherite BaCO3, but in 1790 the English mineralogists Crawford and Cruikshank analyzed this mineral and found that it contained a new "earth", and in the current language, oxide.

Independently of them, the same mineral was studied by another English chemist, Hope. Having come to the same results, he announced that there is a new element in strontianite - the metal strontium.

Apparently, the discovery was already “in the air”, because almost simultaneously the prominent German chemist Klaproth announced the discovery of a new “earth”.

In the same years, the well-known Russian chemist, Academician Toviy Egorovich Lovitz, also came across traces of "strontium earth". He had long been interested in the mineral known as heavy spar. In this mineral (its composition is BaSO4), Karl Scheele discovered in 1774 the oxide of the new element barium. We do not know why Lovitz was not indifferent to heavy spar; it is only known that the scientist, who discovered the adsorption properties of coal and did much more in the field of general and organic chemistry, collected samples of this mineral. But Lovitz was not just a collector, he soon began to systematically study heavy spar and in 1792 came to the conclusion that this mineral contained an unknown impurity. He managed to extract quite a lot from his collection - more than 100 g of new "earth" and continued to explore its properties. The results of the study were published in 1795.

So, almost simultaneously, several researchers in different countries came close to the discovery of strontium. But in its elementary form it was singled out only in 1808.

The outstanding scientist of his time, Humphry Davy, already understood that the element of strontium earth must, apparently, be an alkaline earth metal, and he obtained it by electrolysis, i.e. in the same way as calcium, magnesium, barium. More specifically, the world's first metallic strontium was obtained by electrolysis of its moistened hydroxide. The strontium released at the cathode instantly combined with mercury, forming an amalgam. Decomposing the amalgam by heating, Davy isolated the pure metal.

Strontium metal is now produced by the aluminothermic process. SrO oxide is mixed with aluminum powder or shavings and at a temperature of 1100 ... 1150 ° C in an electric vacuum furnace (pressure of 0.01 mm Hg) the reaction begins:

4SrO + 2Al → 3Sr + Al 2 O 3 SrO.

The electrolysis of strontium compounds (the method used by Davy) is less efficient.

Applications of metallic strontium

Strontium is an active metal. This prevents its wide application in technology. But, on the other hand, the high chemical activity of strontium makes it possible to use it in certain areas of the national economy. In particular, it is used in the smelting of copper and bronze - strontium binds sulfur, phosphorus, carbon and increases the fluidity of the slag. Thus, strontium contributes to the purification of the metal from numerous impurities. In addition, the addition of strontium increases the hardness of copper, almost without reducing its electrical conductivity. Strontium is introduced into electric vacuum tubes to absorb the remaining oxygen and nitrogen, to make the vacuum deeper. Repeatedly purified strontium is used as a reducing agent in the production of uranium.

Additionally:

Strontium-90 (English strontium-90) - radioactive nuclide chemical element strontium With atomic number 38 andmass number 90. It is formed mainly during nuclear fission in nuclear reactors and nuclear weapons.

into the environment 90 Sr enters mainly during nuclear explosions and emissions from NPP.

Strontium is an analogue calcium and is able to be firmly deposited in the bones. Long-term radiation exposure 90 Sr and its decay products affect bone tissue and bone marrow, which leads to the development radiation sickness, tumors of hematopoietic tissue and bones.

Application:

90 Sr applied in production radioisotope energy sources in the form of strontium titanate (density 4.8 g/cm³, energy release about 0.54 W/cm³).

One of the widest applications 90 Sr - control sources of dosimetric devices, including military and civil defense. The most common - type "B-8" is made as a metal substrate containing in the recess a drop of epoxy resin containing the compound 90 Sr. To ensure protection against the formation of radioactive dust through erosion, the preparation is covered with a thin layer of foil. In fact, such sources of ionizing radiation are a complex 90 sr- 90 Y, since yttrium is continuously formed during the decay of strontium. 90 sr- 90 Y is an almost pure beta source. Unlike gamma-radioactive drugs, beta drugs are easy to shield with a relatively thin (about 1 mm) steel layer, which led to the choice of a beta drug for testing purposes, starting from the second generation of military dosimetric equipment (DP-2, DP-12, DP- 63).

Strontium is a silvery white, soft, ductile metal. Chemically, it is very active, like all alkaline earth metals. Oxidation state + 2. Strontium directly combines when heated with halogens, phosphorus, sulfur, carbon, hydrogen and even nitrogen (at temperatures above 400 ° C).

Conclusion

So, strontium is often used in chemistry, metallurgy, peretechnics, atomic hydrogen energy, and so on. And therefore, this chemical element is more and more confidently making its way into the industry, the demand for it is constantly growing. Strontium is also useful in medicine. The effect on the human body of natural strontium (low-toxic, widely used to treat osteoporosis). Radioactive strontium almost always has a negative effect on the human body.

But will nature be able to satisfy the needs of mankind in this metal?

In nature, there are quite large so-called volcanogenic-sedimentary deposits of strontium, for example, in the deserts of California and Arizona in the USA (By the way, it has been noticed that strontium “loves” a hot climate, so it is much less common in northern countries.). In the Tertiary era, this area was the scene of violent volcanic activity.

Thermal waters, rising along with lava from the bowels of the earth, were rich in strontium. Lakes located among volcanoes accumulated this element, forming very solid reserves of it over the millennia.

There is also strontium in the waters of Kara-Bogaz-Gol. The constant evaporation of the waters of the bay leads to the fact that the concentration of salts continuously increases and finally reaches the saturation point - the salts precipitate. The content of strontium in these sediments is sometimes 1 - 2%.

A few years ago, geologists discovered a significant deposit of celestite in the mountains of Turkmenistan. The blue layers of this valuable mineral lie on the slopes of the gorges and deep canyons of Kushtangtau, a mountain range in the southwestern part of Pamir-Alay. There is no doubt that the Turkmen "heavenly" stone will successfully serve our national economy.

Haste is not characteristic of nature: now man is using the reserves of strontium, which she began to create millions of years ago. But even today, in the depths of the earth, in the depths of the seas and oceans, complex chemical processes take place, accumulations of valuable elements arise, new treasures are born, but they will not be inherited by us, but by our distant, distant descendants.

Bibliography

Encyclopedia Around the World

http://www.krugosvet.ru/enc/nauka_i_tehnika/himiya/STRONTSI.html?page=0.3

Wikipedia "Strontium"

http://ru.wikipedia.org/wiki/%D0%A1%D1%82%D1%80%D0%BE%D0%BD%D1%86%D0%B8%D0%B9

3.Popular library of chemical elements