Atomic mass of strontium. Strontium and its characteristics

Strontium is 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 designated by the symbol Sr (lat. Strontium). The simple substance strontium (CAS number: 7440-24-6) is a soft, malleable and ductile silver-white alkaline earth metal. It has a high chemical activity, in air it quickly reacts with moisture and oxygen, becoming covered with a yellow oxide film.

History and origin of the name

The new element was discovered in the mineral strontianite, found in 1764 in a lead mine near the Scottish village of Stronshian, which later gave the name to the new element. The presence of a new metal oxide in this mineral was established in 1787 by William Cruikshank and Ader Crawford. Highlighted in pure form Sir Humphrey Davy in 1808.

Receipt

There are 3 ways to obtain metallic strontium:
1. thermal decomposition of some compounds
2. electrolysis
3. reduction of oxide or chloride
Main industrial way obtaining metallic strontium is the thermal reduction of its oxide with aluminum. Further, the resulting strontium is purified by sublimation.
The electrolytic production of strontium by electrolysis of a melt of a mixture of SrCl 2 and NaCl has not become widespread due to the low current efficiency and contamination of strontium with impurities.
During thermal decomposition of strontium hydride or nitride, finely dispersed strontium is formed, which is prone to easy ignition.

Chemical properties

Strontium in its compounds always exhibits a +2 valency. By properties, strontium is close to calcium and barium, occupying an intermediate position between them.
In the electrochemical series of voltages, strontium is among the most active metals(its normal electrode potential is −2.89 V). Reacts vigorously with water to form hydroxide:
Sr + 2H 2 O \u003d Sr (OH) 2 + H 2

Reacts with acids heavy metals from their salts. With concentrated acids (H 2 SO 4 , HNO 3) reacts weakly.
Strontium metal rapidly oxidizes in air, forming a yellowish film, in which, in addition to SrO oxide, SrO 2 peroxide and Sr 3 N 2 nitride are always present. When heated in air, it ignites; powdered strontium in air is prone to self-ignition.
Vigorously reacts with non-metals - sulfur, phosphorus, halogens. Interacts with hydrogen (above 200°C), nitrogen (above 400°C). Practically does not react with alkalis.
At high temperatures reacts with CO 2 to form a carbide:
5Sr + 2CO 2 = SrC 2 + 4SrO

Easily soluble salts of strontium with anions Cl - , I - , NO 3 - . Salts with anions F -, SO 4 2-, CO 3 2-, PO 4 3- are sparingly soluble.

Strontium- alkaline earth metal. It is a substance of a silvery-white color (see photo), very soft and plastic, easily cut even with an ordinary knife. Possesses high activity, burns in the presence of air, enters into chemical interactions with water. AT natural conditions not found in pure form. It is mainly found in the composition of fossil minerals, usually in combination with calcium.

It was first found in Scotland at the end of the 18th century in a village with the name Stronshian, which gave the name to the found mineral - strontianite. But only 30 years after the discovery, the English scientist H. Davy was able to isolate it in its pure form.

Element compounds are used in metallurgical production, medicine, Food Industry. Very interesting is its property, when burning, to emit fires of a red hue, which were adopted by pyrotechnics at the beginning of the 20th century.

The action of strontium and its biological role

Many associate the action of a macroelement with high toxicity and radioactivity. But such an opinion is rather erroneous, because. the natural element practically does not possess these qualities and is even present in tissues biological organisms, performing an important biological role and some functions as a satellite of calcium. Due to the properties of the substance, it is used for medical purposes.

The main accumulation of strontium in the human body falls on bone tissue. This is due to the fact that the element is similar to calcium in chemical action, and calcium, in turn, is the main component of the "construction" of the skeleton. But the muscles contain only 1% of the total mass of the element in the body.

Also, strontium is present in the deposits of gall and urinary stones, again in the presence of calcium.

By the way, about the harmfulness of strontium - only radioactive isotopes have a devastating effect on health, who in their own way chemical properties practically indistinguishable from the natural element. Perhaps this is the reason for this confusion.

Daily rate

The daily norm of a macronutrient is approximately 1 mg. This amount is quite easily replenished with food and drinking water. In total, approximately 320 mg of strontium is distributed in the body.

But it should be borne in mind that our body is able to absorb only 10% of the incoming element, and we get up to 5 mg per day.

Strontium deficiency

The lack of a macronutrient can only theoretically cause some pathologies, but so far this has been shown only in animal experiments. So far, scientists have not identified negative impact strontium deficiency on the human body.

On the this moment only some dependences of the assimilation of this macronutrient under the influence of other substances in the body have been identified. For example, this process is facilitated by certain amino acids, the intake of vitamins D and lactose. And drugs based on barium or sodium sulfates, as well as products with a high content of dietary coarse fibers, have an opposite effect.

There is another unpleasant feature - when calcium deficiency occurs, the body begins to accumulate radioactive strontium even from the air (often polluted by industrial enterprises).

Why is strontium dangerous for humans and what is its harm?

Strontium, after all, is capable of exerting a harmful radioactive effect. The element itself does little harm, and a critical dose has not yet been established. But its isotopes can cause diseases and various disorders. Like natural strontium, it accumulates in the skeleton itself, but its action causes damage to the bone marrow and destruction of the very structure of the bones. It can affect the cells of the brain and liver, and thus cause the occurrence of neoplasms and tumors.

But one of the most terrible consequences of exposure to the isotope is radiation sickness. The consequences of the Chernobyl disaster are still being felt in our country, and the accumulated reserves of radioactive strontium make themselves felt in the soil, water and the atmosphere itself. You can also get a large dose by working at enterprises using the element - there high level bone sarcoma and leukemia.

But natural strontium can also cause unpleasant consequences. Due to a rather rare set of circumstances such as an inadequate diet, a lack of calcium, vitamin D, and an imbalance in the body of elements such as selenium and molybdenum, specific diseases develop - strontium rickets and uric disease. The latter got its name from the area where they suffered in the 19th century locals. They became disabled due to the curvature of the structure of the skeleton, bones and joints. Moreover, for the most part, those people who grew up in these places from childhood suffered. Only in the 20th century did they find out that the waters of the local river contained an increased amount of the element. And during the period of growth, it is the musculoskeletal system that is most affected.

Contact with strontium oxide on the mucous membranes of the mouth or eyes can cause burns and deep damage. And inhaling it with air can contribute to the development of pathological diseases in the lungs - fibrosis, bronchitis, and heart failure is also possible.

As treatment, drugs based on calcium, magnesium, sodium sulfate or barium are usually used. It is also possible to use complexing agents that bind and remove radioactive toxins from cells.

Getting into the soil, the toxic isotope of strontium is thus able to accumulate in plant fibers, and then in animal organisms. Thus, the human body slowly but surely accumulates toxins by consuming poisoned foods. Might save the day a little heat treatment products, which contributes to a fairly significant reduction in the content of harmful toxin in them.

This radionuclide is very difficult to remove from the body, because it may take him almost half a year to get rid of at least half of the accumulated stock.

What food contains?

Indications for treatment with drugs based on this element

There are still indications for the appointment of a macroelement, despite its possible toxicity. And even a radioactive isotope is used for medical purposes. Its radiation in allowed doses can have a therapeutic effect on erosions, tumors on the skin and mucous membranes. With deeper foci, this method is already used.

Also, its compounds serve as drugs for the treatment of epilepsy, nephritis and correction of deformities in childhood orthopedists. To some extent, it can serve as an antihelminthic agent.

DEFINITION

Strontium- thirty-eighth element 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.).

Metal strontium in the form a simple substance is a soft silver-white (Fig. 1) metal with malleability and ductility (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 weight match. 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 found wide application in metallurgy as an alloying component of copper-based alloys.

Examples of problem solving

EXAMPLE 1

STRONTIUM (Strontium, Sr) - chemical element periodic system D. I. Mendeleev, subgroups of alkaline earth metals. In the human body, S. competes with calcium (see) for inclusion in crystal lattice oxyapatite bones (see). 90 Sr, one of the longest-lived radioactive fission products of uranium (see), accumulating in the atmosphere and biosphere during testing nuclear weapons(see), represents a great danger to mankind. S.'s radioactive isotopes are used in medicine for radiation therapy (see), as a radioactive label in diagnostic radiopharmaceuticals (see) in medical biol. research, as well as in atomic electric batteries. S. compounds are used in flaw detectors, in sensitive instruments, in devices for combating static electricity, in addition, S. is used in radio electronics, pyrotechnics, metallurgical, chemical industry and in the manufacture of ceramic products. S.'s connections are not poisonous. When working with metal S., one should be guided by the rules for handling alkali metals(see) and alkaline earth metals (see).

S. was discovered as part of a mineral later named SrC03 strontianite in 1787 near the Scottish city of Strontiana.

The serial number of strontium is 38, the atomic weight (mass) is 87.62. The content of S. in the earth's crust averages 4-10 2 wt. %, in sea ​​water- 0.013% (13 mg/l). The minerals strontianite and celestite SrSO 4 are of industrial importance.

The human body contains approx. 0.32 g strontium, mostly in bone tissue, in the blood, the concentration of C. is normally 0.035 mg / l, in the urine - 0.039 mg / l.

S. is a soft silvery-white metal, t°pl 770°, t°kip 1383°.

According to chem. S.'s properties are similar to calcium and barium (see), in compounds the valence of strontium is 4-2, it is chemically active, it is oxidized at normal conditions water with the formation of Sr (OH) 2, as well as oxygen and other oxidizing agents.

S. enters the human body hl. arr. with plant foods, as well as with milk. It is absorbed in the small intestine and quickly exchanges with S. contained in the bones. S.'s removal from an organism is strengthened by complexes, amino acids, polyphosphates. The increased content of calcium and fluorine (see) in water interferes with S.'s cumulation in bones. With an increase in the concentration of calcium in the diet by 5 times, S.'s accumulation in the body is halved. Excessive S.'s intake with food and water due to its increased content in the soil of some geochemical. provinces (for example, in separate districts Eastern Siberia) causes an endemic disease - Urov's disease (see Kashin-Beck disease).

In bones, blood and other biol. S.'s substrates define hl. arr. spectral methods (see Spectroscopy).

radioactive strontium

Natural S. consists of four stable isotopes with mass numbers 84, 86, 87, and 88, of which the latter is the most common (82.56%). Eighteen radioactive isotopes of sulfur are known (with mass numbers 78–83, 85, 89–99) and four isomers of isotopes with mass numbers 79, 83, 85, and 87 (see Isomerism).

In medicine, 90Sr is used for radiation therapy in ophthalmology and dermatology, as well as in radiobiological experiments as a source of β-radiation. 85Sr is obtained either by irradiation in nuclear reactor neutrons of a strontium target enriched in the isotope 84Sr, according to the reaction 84Sr (11.7) 85Sr, or produced on a cyclotron by irradiating natural rubidium targets with protons or deuterons, for example, according to the reaction 85Rb (p, n) 85Sr. The radionuclide 85Sr decays with electron capture, emitting gamma radiation with an energy E gamma equal to 0.513 MeV (99.28%) and 0.868 MeV (< 0,1%).

87mSr can also be obtained by irradiating a strontium target in a reactor by the reaction 86Sr (n, gamma) 87mSr, but the yield of the desired isotope is low, in addition, 85Sr and 89Sr isotopes are formed simultaneously with 87mSr. Therefore, usually 87niSr is obtained using an isotope generator (see Radioactive Isotope Generators) based on the parent isotope of yttrium-87 - 87Y (T1 / 2 = 3.3 days). 87mSr decays with an isomeric transition, emitting gamma radiation with an Egamma energy of 0.388 MeV, and partly with electron capture (0.6%).

89Sr is contained in fission products together with 90Sr; therefore, 89Sr is obtained by irradiating natural sulfur in a reactor. In this case, an 85Sr impurity is also inevitably formed. The 89Sr isotope decays with the emission of P-radiation with an energy of 1.463 MeV (approx. 100%). The spectrum also contains a very weak line of gamma radiation with an energy E gamma equal to 0.95 MeV (0.01%).

90Sr is obtained by isolation from a mixture of uranium fission products (see). This isotope decays with the emission of beta radiation with an energy of E beta equal to 0.546 Meu (100%), without accompanying gamma radiation. The decay of 90Sr leads to the formation of a daughter radionuclide 90Y, which decays (T1 / 2 = 64 hours) with the emission of p-radiation, consisting of two components with Ep equal to 2.27 MeV (99%) and 0.513 MeV (0 .02%). The decay of 90Y also emits very weak gamma radiation with an energy of 1.75 MeV (0.02%).

Radioactive isotopes 89Sr and 90Sr, present in the waste of the nuclear industry and formed during nuclear weapons testing, during contamination environment can enter the human body with food, water, air. Quantification of S.'s migration in the biosphere is usually carried out in comparison with calcium. In most cases, when 90Sr moves from the previous link in the chain to the next, the concentration of 90Sr decreases per 1 g of calcium (the so-called discrimination coefficient), in adults in the body-diet link, this coefficient is 0.25.

Like soluble compounds of other alkaline earth elements, soluble compounds of S. are well absorbed from went. - kish. a path (10-60%), absorption of poorly soluble connections S. (eg, SrTi03) makes less than 1%. The degree of absorption of S.'s radionuclides in the intestine depends on age. With an increase in the calcium content in the diet, S.'s accumulation in the body decreases. Milk promotes increase in S.'s absorption and calcium in intestines. It is believed that this is due to the presence of lactose and lysine in milk.

When inhaled, soluble S. compounds are quickly eliminated from the lungs, while poorly soluble SrTi03 is exchanged in the lungs extremely slowly. Penetration of radionuclide S. through the intact skin makes apprx. one%. Through damaged skin (cut wound, burns, etc.)? as well as from subcutaneous tissue and muscle tissue, S. is absorbed almost completely.

S. is an osteotropic element. Regardless of the route and rhythm of entry into the body, soluble 90Sr compounds selectively accumulate in the bones. Less than 1% of 90Sr is retained in soft tissues.

With intravenous administration, S. is very quickly eliminated from the bloodstream. Soon after administration, the concentration of S. in the bones becomes 100 times or more higher than in soft tissues. Nek-ry distinctions in accumulation 90Sr in separate bodies and fabrics are noted. A relatively higher concentration of 90Sr in experimental animals is found in the kidneys, salivary and thyroid glands, and the lowest - in the skin, bone marrow and adrenal glands. The concentration of 90Sr in the renal cortex is always higher than in the medulla. S. initially lingers on the bone surfaces (periosteum, endosteum), and then is distributed relatively evenly throughout the entire volume of the bone. However, the distribution of 90Sr in various parts the same bone and in different bones is uneven. During the first time after injection, the concentration of 90Sr in the epiphysis and metaphysis of the bone of experimental animals is approximately 2 times higher than in the diaphysis. From the epiphysis and metaphysis, 90Sr is excreted faster than from the diaphysis: in 2 months. the concentration of 90Sr in the epiphysis and metaphysis of the bone decreases by 4 times, and in the diaphysis almost does not change. Initially 90Sr concentrates in those sites in which there is an active formation of a bone. Abundant blood and lymph circulation in the epimetaphyseal areas of the bone contributes to a more intense deposition of 90Sr in them compared to the diaphysis of the tubular bone. The amount of 90Sr deposition in the bones of animals is not constant. A sharp decrease in 90Sr fixation in bones with age was found in all animal species. Deposition of 90Sr in the skeleton significantly depends on gender, pregnancy, lactation, and the state of the neuroendocrine system. A higher deposition of 90Sr in the skeleton was noted in male rats. In the skeleton of pregnant females, 90Sr accumulates less (up to 25%) than in control animals. Lactation has a significant effect on the accumulation of 90Sr in the skeleton of females. With the introduction of 90Sr 24 hours after birth, 90Sr is retained in the skeleton of rats 1.5-2 times less than in non-lactating females.

The penetration of 90Sr into the tissues of the embryo and fetus depends on the stage of their development, the state of the placenta, and the duration of circulation of the isotope in the mother's blood. Penetration of 90Sr into the fetus is the greater, the longer the gestational age at the time of administration of the radionuclide.

To reduce the damaging effect of strontium radionuclides, it is necessary to limit their accumulation in the body. For this purpose, when the skin is contaminated, it is necessary to quickly decontaminate its open areas (Protection-7 preparation, Era or Astra washing powders, NEDE paste). In case of oral intake of strontium radionuclides, antidotes should be used to bind or absorb the radionuclide. Such antidotes include activated barium sulfate (adso-bar), polysurmin, alginic acid preparations, etc. For example, the drug adsobar, when taken immediately after radionuclides enter the stomach, reduces their absorption by 10-30 times. Adsorbents and antidotes should be prescribed immediately after detection of damage by strontium radionuclides, since delay in this case leads to a sharp decrease in their positive effect. At the same time, it is recommended to prescribe emetics (apomorphine) or to produce abundant gastric lavage, use saline laxatives, cleansing enemas. In case of damage by dust-like preparations, abundant washing of the nose and oral cavity, expectorants (thermopsis with soda), ammonium chloride, injections of calcium preparations, diuretics are necessary. In more late dates after the defeat, to reduce the deposition of radionuclides S. in the bones, it is recommended to use the so-called. stable strontium (S. lactate or S. gluconate). Large doses of oral calcium or intravenous MofyT replace stable strontium preparations if these are not available. In connection with the good reabsorption of strontium radionuclides in the renal tubules, the use of diuretics is also indicated.

Nek-swarm decrease in accumulation of radionuclides S. in an organism can be reached by creation competitive relations between them and a stable isotope of C. or calcium, as well as the creation of a deficiency of these elements in cases where the C. radionuclide has already been fixed in the skeleton. However, effective means of decorporation of radioactive strontium from the body have not yet been found.

The minimum significant activity that does not require registration or permission from the State Sanitary Inspection for 85mSr, 85Sr, 89Sr and 90Sr is 3.5*10 -8 , 10 -10 , 2.8*10 -11 and 1.2*10, respectively -12 curies/l.

Bibliography: Borisov V.P. and others. Emergency care for acute radiation exposure, M., 1976; Buldakov L. A. and Moskalev Yu. I. Problems of distribution and experimental estimation of admissible levels of Cs137, Sr90 and Ru106, M., 1968, bibliogr.; Voinar A. I. The biological role of trace elements in the body of animals and humans, p. 46, M., 1960; Ilyin JI. A. and Ivannikov A. T. radioactive substances and wounds, M., 1979; To and with and in fi-on B. S. and T about r ben to about V. P. Life of a bone tissue, M., 1979; JI e in and V. I N. Obtaining radioactive preparations, M., 1972; Metabolism of strontium, ed. J. M. A. Lenihena and others, trans. from English, M., 1971; Poluektov N. S. and others. Analytical chemistry of strontium, M., 1978; P e m and G. Course not organic chemistry, per. from German, vol. 1, M., 1972; Protection of the patient in radionuclide investigations, Oxford, 1969, bibliogr.; Table of isotopes, ed. by C. M. Lederer a. V. S. Shirley, N. Y. a. o., 1978.

A. V. Babkov, Yu. I. Moskalev (rad.).

Strontium- an element of the main subgroup of the second group, the fifth period of the periodic system chemical elements D. I. Mendeleev, with atomic number 38. 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.

Thus, 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.