All about calcium chemistry. Calcium (Ca, Calcium). Shale ash cyclones

Calcium

CALCIUM-I; m.[from lat. calx (calcis) - lime] Chemical element (Ca), silvery metal white color, which is part of limestone, marble, etc.

◁ Calcium, th, th. K salts.

calcium

(lat. Calcium), a chemical element of group II of the periodic system, belongs to the alkaline earth metals. Name from lat. calx, genitive calcis - lime. Silver-white metal, density 1.54 g / cm 3, t pl 842ºC. At normal temperatures, it easily oxidizes in air. In terms of prevalence in the earth's crust, it occupies the 5th place (minerals calcite, gypsum, fluorite, etc.). As an active reducing agent, it is used to obtain U, Th, V, Cr, Zn, Be and other metals from their compounds, to deoxidize steels, bronzes, etc. It is included in the composition of antifriction materials. Calcium compounds are used in construction (lime, cement), calcium preparations - in medicine.

CALCIUM

CALCIUM (lat. Calcium), Ca (read "calcium"), a chemical element with atomic number 20, is located in the fourth period in group IIA of the periodic system of Mendeleev's elements; atomic mass 40.08. Belongs to the number of alkaline earth elements (cm. ALKALINE EARTH METALS).
Natural calcium consists of a mixture of nuclides (cm. NUCLIDE) with mass numbers 40 (in a mixture by mass 96.94%), 44 (2.09%), 42 (0.667%), 48 (0.187%), 43 (0.135%) and 46 (0.003%). Outer electron layer configuration 4 s 2 . In almost all compounds, the oxidation state of calcium is +2 (valency II).
The radius of the neutral calcium atom is 0.1974 nm, the radius of the Ca 2+ ion is from 0.114 nm (for the coordination number 6) to 0.148 nm (for the coordination number 12). The sequential ionization energies of a neutral calcium atom are 6.133, 11.872, 50.91, 67.27, and 84.5 eV, respectively. On the Pauling scale, the electronegativity of calcium is about 1.0. IN free form calcium is a silvery white metal.
Discovery history
Calcium compounds are found everywhere in nature, so mankind has been familiar with them since ancient times. Lime has been used in the construction industry for a long time. (cm. LIME)(quicklime and slaked), which for a long time was considered a simple substance, "earth". However, in 1808 the English scientist G. Davy (cm. DEVI Humphrey) managed to get a new metal from lime. To do this, Davy subjected to electrolysis a mixture of slightly moistened slaked lime with mercury oxide and isolated a new metal from the amalgam formed on the mercury cathode, which he called calcium (from Latin calx, genus case calcis - lime). In Russia, for some time this metal was called "limestone".
Being in nature
Calcium is one of the most abundant elements on earth. It accounts for 3.38% of the mass of the earth's crust (5th place in abundance after oxygen, silicon, aluminum and iron). Due to the high chemical activity of calcium in the free form in nature is not found. Most of the calcium is found in silicates. (cm. SILICATES) and aluminosilicates (cm. ALUMOSILICATES) various rocks(granites (cm. GRANITE), gneisses (cm. GNEISS) and so on.). As sedimentary rocks calcium compounds are represented by chalk and limestone, consisting mainly of the mineral calcite (cm. CALCITE)(CaCO3). The crystalline form of calcite - marble - is found in nature much less frequently.
Calcium minerals such as limestone are quite widespread. (cm. LIMESTONE)СaCO 3 , anhydrite (cm. ANHYDRITE) CaSO 4 and gypsum (cm. GYPSUM) CaSO 4 2H 2 O, fluorite (cm. FLUORITE) CaF 2 , apatite (cm. APATITE) Ca 5 (PO 4) 3 (F, Cl, OH), dolomite (cm. DOLOMITE) MgCO 3 CaCO 3. The presence of calcium and magnesium salts in natural water determines its hardness. (cm. HARDNESS OF WATER). A significant amount of calcium is part of living organisms. So, hydroxylapatite Ca 5 (PO 4) 3 (OH), or, in another entry, 3Ca 3 (PO 4) 2 Ca (OH) 2 - the basis of the bone tissue of vertebrates, including humans; shells and shells of many invertebrates, egg shells, etc. are made of calcium carbonate CaCO 3.
Receipt
Calcium metal is obtained by electrolysis of a melt consisting of CaCl 2 (75-80%) and KCl or from CaCl 2 and CaF 2, as well as aluminothermic reduction of CaO at 1170-1200 ° C:
4CaO + 2Al = CaAl 2 O 4 + 3Ca.
Physical and Chemical properties
Calcium metal exists in two allotropic modifications(see Allotropy (cm. ALLOTROPY)). Up to 443 °C, a-Ca with a cubic face-centered lattice is stable (parameter a = 0.558 nm), above b-Ca is stable with a cubic body-centered lattice of the a-Fe type (parameter a = 0.448 nm). The melting point of calcium is 839 ° C, the boiling point is 1484 ° C, the density is 1.55 g / cm 3.
The chemical activity of calcium is high, but lower than that of all other alkaline earth metals. It easily reacts with oxygen, carbon dioxide and moisture in the air, due to which the surface of calcium metal is usually dull gray, so in the laboratory calcium is usually stored, like other alkaline earth metals, in a tightly closed jar under a layer of kerosene.
In the series of standard potentials, calcium is located to the left of hydrogen. The standard electrode potential of the Ca 2+ /Ca 0 pair is -2.84 V, so that calcium actively reacts with water:
Ca + 2H 2 O \u003d Ca (OH) 2 + H 2.
With active non-metals (oxygen, chlorine, bromine), calcium reacts under normal conditions:
2Ca + O 2 \u003d 2CaO; Ca + Br 2 \u003d CaBr 2.
When heated in air or oxygen, calcium ignites. With less active non-metals (hydrogen, boron, carbon, silicon, nitrogen, phosphorus and others), calcium interacts when heated, for example:
Ca + H 2 \u003d CaH 2 (calcium hydride),
Ca + 6B = CaB 6 (calcium boride),
3Ca + N 2 = Ca 3 N 2 (calcium nitride)
Ca + 2C \u003d CaC 2 (calcium carbide)
3Ca + 2P = Ca 3 P 2 (calcium phosphide), calcium phosphides of CaP and CaP 5 compositions are also known;
2Ca + Si \u003d Ca 2 Si (calcium silicide), calcium silicides of the compositions CaSi, Ca 3 Si 4 and CaSi 2 are also known.
The course of the above reactions, as a rule, is accompanied by the release of a large amount of heat (i.e., these reactions are exothermic). In all compounds with non-metals, the oxidation state of calcium is +2. Most of the calcium compounds with non-metals are easily decomposed by water, for example:
CaH 2 + 2H 2 O \u003d Ca (OH) 2 + 2H 2,
Ca 3 N 2 + 3H 2 O \u003d 3Ca (OH) 2 + 2NH 3.
Calcium oxide is typically basic. In the laboratory and technology, it is obtained by thermal decomposition of carbonates:
CaCO 3 \u003d CaO + CO 2.
Technical calcium oxide CaO is called quicklime.
It reacts with water to form Ca (OH) 2 and release a large amount of heat:
CaO + H 2 O \u003d Ca (OH) 2.
Ca (OH) 2 obtained in this way is usually called slaked lime or lime milk (cm. LIME MILK) due to the fact that the solubility of calcium hydroxide in water is low (0.02 mol / l at 20 ° C), and when it is added to water, a white suspension is formed.
When interacting with acid oxides, CaO forms salts, for example:
CaO + CO 2 \u003d CaCO 3; CaO + SO 3 \u003d CaSO 4.
The Ca 2+ ion is colorless. When calcium salts are added to the flame, the flame turns brick red.
Calcium salts such as CaCl 2 chloride, CaBr 2 bromide, CaI 2 iodide and Ca(NO 3) 2 nitrate are highly soluble in water. CaF 2 fluoride, CaCO 3 carbonate, CaSO 4 sulfate, Ca 3 (PO 4) 2 average orthophosphate, CaC 2 O 4 oxalate and some others are insoluble in water.
Important is the fact that, unlike the average calcium carbonate CaCO 3, acidic calcium carbonate (hydrocarbonate) Ca (HCO 3) 2 is soluble in water. In nature, this leads to following processes. When cold rain or river water, saturated with carbon dioxide, penetrates underground and falls on limestones, their dissolution is observed:
CaCO 3 + CO 2 + H 2 O \u003d Ca (HCO 3) 2.
In the same places where water saturated with calcium bicarbonate comes to the surface of the earth and heats up sunbeams, the reverse reaction takes place:
Ca (HCO 3) 2 \u003d CaCO 3 + CO 2 + H 2 O.
So in nature there is a transfer of large masses of substances. As a result, huge dips can form underground (see Karst (cm. Karst (natural phenomenon))), and beautiful stone "icicles" - stalactites are formed in the caves (cm. STALAPTITES (mineral formations)) and stalagmites (cm. STALAGMITES).
The presence of dissolved calcium bicarbonate in water largely determines the temporary hardness of water. (cm. HARDNESS OF WATER). It is called temporary because when water is boiled, the bicarbonate decomposes, and CaCO 3 precipitates. This phenomenon leads, for example, to the fact that scale forms in the kettle over time.
The use of calcium and its compounds
Metallic calcium is used for metallothermic production of uranium (cm. Uranium (chemical element)), thorium (cm. THORIUM), titanium (cm. TITANIUM (chemical element)), zirconium (cm. ZIRCONIUM), cesium (cm. CESIUM) and rubidium (cm. RUBIDIUM).
Natural calcium compounds are widely used in the production of binders (cement (cm. CEMENT), gypsum (cm. GYPSUM), lime, etc.). The binding effect of slaked lime is based on the fact that over time, calcium hydroxide reacts with carbon dioxide in the air. As a result of the ongoing reaction, needle-like crystals of CaCO3 calcite are formed, which grow into nearby stones, bricks, and other building materials and, as it were, weld them into a single whole. Crystalline calcium carbonate - marble - fine finishing material. Chalk is used for whitewashing. Large quantities of limestone are consumed in the production of pig iron, as they make it possible to transfer refractory impurities of iron ore (for example, quartz SiO 2) into relatively low-melting slags.
As disinfectant very effective bleach (cm. BLEACHING POWDER)- “bleach” Ca(OCl)Cl - mixed chloride and calcium hypochloride (cm. CALCIUM HYPOCHLORITE) with high oxidizing power.
Calcium sulfate is also widely used, existing both in the form of an anhydrous compound and in the form of crystalline hydrates - the so-called "semi-aqueous" sulfate - alabaster (cm. ALEVIZ FRYAZIN (Milanese)) CaSO 4 0.5H 2 O and two-water sulfate - gypsum CaSO 4 2H 2 O. Gypsum is widely used in construction, in sculpture, for the manufacture of stucco and various art products. Gypsum is also used in medicine to fix bones in case of fractures.
Calcium chloride CaCl 2 is used along with table salt to combat glaciation pavement. Calcium fluoride CaF 2 is an excellent optical material.
calcium in the body
Calcium is a biogenic element (cm. BIOGENIC ELEMENTS), constantly present in the tissues of plants and animals. Important Component mineral metabolism of animals and humans and the mineral nutrition of plants, calcium performs a variety of functions in the body. Contains apatite (cm. APATITE), as well as calcium sulfate and carbonate forms the mineral component of bone tissue. The human body weighing 70 kg contains about 1 kg of calcium. Calcium is involved in the work of ion channels (cm. ION CHANNELS), carrying out the transport of substances through biological membranes, in the transmission of a nerve impulse (cm. NERVE IMPULSE), in the process of blood coagulation (cm. BLOOD COAGULATION) and fertilization. Calciferols regulate calcium metabolism in the body (cm. CALCIFEROLS)(vitamin D). Lack or excess of calcium leads to various diseases - rickets (cm. RICKETS), calcification (cm. CALCINOSIS) etc. Therefore, human food should contain calcium compounds in the right quantities (800-1500 mg of calcium per day). Calcium content is high in dairy products (such as cottage cheese, cheese, milk), some vegetables and other foods. Calcium preparations are widely used in medicine.

encyclopedic Dictionary . 2009 .

Synonyms:

See what "calcium" is in other dictionaries:

- (Ca) yellow shiny and malleable metal. Specific gravity 1.6. Dictionary foreign words included in the Russian language. Pavlenkov F., 1907. CALCIUM (new lat. calcium, from lat. calx lime). Silver colored metal. Dictionary of foreign words, ... ... Dictionary of foreign words of the Russian language

CALCIUM- CALCIUM, Calcium, chem. element, char. Ca, shiny, silvery white metal with crystalline. fracture, belonging to the group of alkaline earth metals. Oud. weight 1.53; at. V. 40.07; melting point 808°. Sa is one of the very ... ... Big Medical Encyclopedia

- (Calcium), Ca, a chemical element of group II of the periodic system, atomic number 20, atomic mass 40.08; refers to alkaline earth metals; mp 842shC. Contained in the bone tissue of vertebrates, mollusk shells, eggshells. Calcium ... ... Modern Encyclopedia

The metal is silvery white, viscous, malleable, rapidly oxidizing in air. Melting rate pa 800 810°. In nature, it occurs in the form of various salts, which form deposits of chalk, limestone, marble, phosphorites, apatites, gypsum, etc. On the yellow. dor… … Technical railway dictionary

- (lat. Calcium) Ca, a chemical element of group II of the periodic system, atomic number 20, atomic mass 40.078, belongs to the alkaline earth metals. The name is from the Latin calx, genitive calcis lime. Silvery white metal, ... ... Big Encyclopedic Dictionary

- (symbol Ca), a widespread silvery-white metal from the ALKALINE EARTH group, was first isolated in 1808. It is found in many rocks and minerals, especially in limestone and gypsum, as well as in bones. Contributes to the body... Scientific and technical encyclopedic dictionary

Ca (from lat. Calx, genus calcis lime *a. calcium; n. Kalzium; f. calcium; and. calcio), chem. element II group periodic. systems of Mendeleev, at.s. 20, at. m. 40.08. It consists of six stable isotopes: 40Ca (96.97%), 42Ca (0.64%), ... ... Geological Encyclopedia

CALCIUM, calcium, pl. no, husband. (from lat. calx lime) (chemical). The chemical element is a silvery-white metal found in lime. Explanatory Dictionary of Ushakov. D.N. Ushakov. 1935 1940 ... Explanatory Dictionary of Ushakov

CALCIUM, me, husband. Chemical element, soft silvery white metal. | adj. calcium, oh, oh. calcium salts. Explanatory dictionary of Ozhegov. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 ... Explanatory dictionary of Ozhegov

Husband. the metal that makes up chemical basis lime. Calcinate what, burn metal, salt or stone. Female calcification. action is, burnout, perekalka. Dahl's Explanatory Dictionary. IN AND. Dal. 1863 1866 ... Dahl's Explanatory Dictionary

Calcium is very common in nature in the form various compounds. In the earth's crust, it occupies the fifth place, accounting for 3.25%, and is most often found in the form of limestone CaCO3, dolomite CaCO3 * MgCO3, gypsum CaSO4 * 2H2O, phosphorite Ca3 (PO4) 2 and fluorspar CaF2, not counting a significant proportion of calcium in composition of silicate rocks. Sea water contains an average of 0.04% (w/w) calcium

Physical and chemical properties of calcium

Calcium is in the subgroup of alkaline earth metals of group II of the periodic system of elements; serial number 20, atomic weight 40.08, valence 2, atomic volume 25.9. Calcium isotopes: 40 (97%), 42 (0.64%), 43 (0.15%), 44 (2.06%), 46 (0.003%), 48 (0.185%). Electronic structure of the calcium atom: 1s2, 2s2p6, 3s2p6, 4s2. The radius of the atom is 1.97 A, the radius of the ion is 1.06 A. Up to 300 ° calcium crystals have the shape of a cube with centered faces and a side size of 5.53 A, above 450 ° - a hexagonal shape. The specific gravity of calcium is 1.542, the melting point is 851°, the boiling point is 1487°, the heat of fusion is 2.23 kcal/mol, the heat of vaporization is 36.58 kcal/mol. Atomic heat capacity of solid calcium Cp = 5.24 + 3.50*10v-3 T for 298-673°K and Cp = 6.29+1.40*10v-3T for 673-1124°K; for liquid calcium Cp = 7.63. Entropy of solid calcium 9.95 ± 1, gaseous at 25° 37.00 ± 0.01.
The vapor pressure of solid calcium was studied by Yu.A. Priselkov and A.N. Nesmeyanov, P. Douglas and D. Tomlin. The values of elasticity of saturated calcium vapor are given in table. 1.

In terms of thermal conductivity, calcium approaches sodium and potassium, at temperatures of 20-100 ° the coefficient of linear expansion is 25 * 10v-6, at 20 ° the electrical resistivity is 3.43 μ ohm / cm3, from 0 to 100 ° the temperature coefficient of electrical resistance is 0.0036. Electrochemical equivalent 0.74745 g/a*h. Tensile strength of calcium 4.4 kg/mm2, Brinell hardness 13, elongation 53%, reduction ratio 62%.
Calcium has a silvery-white color, glistens when broken. In air, the metal is covered with a thin bluish-gray film of nitride, oxide, and partially calcium peroxide. Calcium is flexible and malleable; it can be processed to lathe, drilling, cutting, sawing, pressing, drawing, etc. The purer the metal, the greater its ductility.
In a series of voltages, calcium is located among the most electronegative metals, which explains its high chemical activity. At room temperature, calcium does not react with dry air, at 300 ° and above it is intensively oxidized, and with strong heating it burns with a bright orange-reddish flame. In humid air, calcium is gradually oxidized, turning into hydroxide; With cold water reacts relatively slowly, but hot water vigorously displaces hydrogen, forming hydroxide.
Nitrogen reacts markedly with calcium at 300° and very intensely at 900° to form the nitride Ca3N2. With hydrogen at a temperature of 400°, calcium forms the hydride CaH2. With dry halogens, with the exception of fluorine, calcium does not bind at room temperature; intensive formation of halides occurs at 400° and above.
Strong sulfuric (65-60 ° Be) and nitric acids act weakly on pure calcium. Of the aqueous solutions of mineral acids, hydrochloric acid, strongly nitric acid, and weakly sulfuric acid act very strongly. In concentrated NaOH solutions and in soda solutions, calcium is almost not destroyed.

Application

Calcium finds ever-increasing use in various industries. Recently, it has gained great importance as a reducing agent in the production of a number of metals. Pure uranium metal is obtained by reducing uranium fluoride with calcium metal. Titanium oxides, as well as oxides of zirconium, thorium, tantalum, niobium and other rare metals can be reduced with calcium or its hydrides. Calcium is a good deoxidizer and degasser in the production of copper, nickel, chromium-nickel alloys, special steels, nickel and tin bronzes; it removes sulfur, phosphorus, and carbon from metals and alloys.
Calcium forms refractory compounds with bismuth, so it is used to purify lead from bismuth.
Calcium is added to various light alloys. It contributes to the improvement of the surface of the ingots, fineness and reduction of oxidizability. Bearing alloys containing calcium are widely used. Lead alloys (0.04% Ca) can be used to make cable sheaths.
Calcium is used for the dehydration of alcohols and solvents for the desulfurization of petroleum products. Calcium-zinc alloys or zinc-magnesium alloys (70% Ca) are used to produce high-quality porous concrete. Calcium is a part of antifriction alloys (lead-calcium babbits).
Due to the ability to bind oxygen and nitrogen, calcium or calcium alloys with sodium and other metals are used to purify noble gases and as a getter in vacuum radio equipment. Calcium is also used to produce hydride, which is a source of hydrogen in field conditions. With carbon, calcium forms calcium carbide CaC2, which is used in large quantities to obtain acetylene C2H2.

History of development

Devi first obtained calcium in the form of an amalgam in 1808 using the electrolysis of wet lime with a mercury cathode. Bunsen in 1852 obtained an amalgam with a high calcium content by electrolysis of a hydrochloric acid solution of calcium chloride. Bunsen and Mathyssen in 1855 obtained pure calcium by electrolysis of CaCl2 and Moissan by electrolysis of CaF2. In 1893, Borchers significantly improved the electrolysis of calcium chloride by applying cathode cooling; Arndt in 1902 obtained by electrolysis a metal containing 91.3% Ca. Ruff and Plata used a mixture of CaCl2 and CaF2 to lower the electrolysis temperature; Borchers and Stockem obtained a sponge at a temperature below the melting point of calcium.
Rathenau and Süter solved the problem of electrolytic production of calcium by proposing a method of electrolysis with a touch cathode, which soon became industrial. There have been many proposals and attempts to obtain calcium alloys by electrolysis, especially on a liquid cathode. According to F.O. Banzel, it is possible to obtain calcium alloys by electrolysis of CaF2 with the addition of salts or fluoroxides of other metals. Poulenet and Melan obtained a Ca-Al alloy on a liquid aluminum cathode; Kugelgen and Seward produced a Ca-Zn alloy on a zinc cathode. The production of Ca-Zn alloys was studied in 1913 by V. Moldengauer and J. Andersen, who also obtained Pb-Ca alloys on a lead cathode. Koba, Simkins, and Gire used a 2000 A lead cathode cell and produced an alloy with 2% Ca at a current efficiency of 20%. I. Tselikov and V. Wazinger added NaCl to the electrolyte to obtain an alloy with sodium; R.R. Syromyatnikov stirred the alloy and achieved 40-68% current efficiency. Calcium alloys with lead, zinc and copper are produced by electrolysis on an industrial scale.
The thermal method of obtaining calcium has aroused considerable interest. Aluminothermic reduction of oxides was discovered in 1865 by H.H. Beketov. In 1877, Malet discovered the interaction of a mixture of calcium, barium, and strontium oxides with aluminum when heated. Winkler tried to reduce these same oxides with magnesium; Bilz and Wagner, reducing calcium oxide in vacuum with aluminum, obtained a low yield of the metal. Gunz in 1929 achieved the best results. A.I. Voinitsky in 1938 reduced calcium oxide with aluminum and silico alloys in the laboratory. The method was patented in 1938. At the end of the Second World War, the thermal method was used industrially.
In 1859, Caron proposed a method for obtaining alloys of sodium with alkaline earth metals by the action of metallic sodium on their chlorides. According to this method, calcium (and barine) is obtained in an alloy with lead. Until the Second World War, the industrial production of calcium by electrolysis was carried out in Germany and Fraction. In Biterfeld (Germany) in the period from 1934 to 1939, 5-10 tons of calcium were produced annually. The US demand for calcium was covered by imports, which amounted to 10-25 g per year in the period 1920-1940. Since 1940, when imports from France ceased, the United States began to produce calcium itself in significant quantities by electrolysis; at the end of the war they began to receive calcium by vacuum thermal method; according to S. Loomis, its output reached 4.5 tons per day. According to Minerale Yarbuk, Dominium Magnesium in Canada produced calcium per year:

Information on the scale of calcium release for last years missing.

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Calcium- an element of the 4th period and the PA group of the Periodic System, serial number 20. The electronic formula of the atom is [ 18 Ar] 4s 2, oxidation states +2 and 0. Refers to alkaline earth metals. It has a low electronegativity (1.04), exhibits metallic (basic) properties. Forms (as a cation) numerous salts and binary compounds. Many calcium salts are sparingly soluble in water. In nature - sixth by chemical abundance, the element (the third among metals), is in bound form. A vital element for all organisms. The lack of calcium in the soil is replenished by the application of lime fertilizers (CaCO 3 , CaO, calcium cyanamide CaCN 2, etc.). Calcium, calcium cation and its compounds color the flame of a gas burner in a dark orange color ( qualitative detection).

Calcium Ca

Silver-white metal, soft, ductile. In humid air, it tarnishes and becomes covered with a film of CaO and Ca(OH) 2. Very reactive; ignites when heated in air, reacts with hydrogen, chlorine, sulfur and graphite:

Reduces other metals from their oxides (an industrially important method is calciumthermy):

Receipt calcium in industry:

Calcium is used to remove non-metal impurities from metal alloys, as a component of light and antifriction alloys, to isolate rare metals from their oxides.

Calcium oxide CaO

basic oxide. The technical name is quicklime. White, highly hygroscopic. Has an ionic structure Ca 2+ O 2- . Refractory, thermally stable, volatile on ignition. Absorbs moisture and carbon dioxide from the air. Reacts vigorously with water (high exo- effect), forms a strongly alkaline solution (hydroxide precipitation is possible), the process is called lime slaking. Reacts with acids, metal and non-metal oxides. It is used for the synthesis of other calcium compounds, in the production of Ca (OH) 2, CaC 2 and mineral fertilizers, as a flux in metallurgy, a catalyst in organic synthesis, a component of binders in construction.

Equations of the most important reactions:

Receipt CaO in industry– limestone roasting (900-1200 °С):

CaCO3 = CaO + CO2

Calcium hydroxide Ca(OH) 2

basic hydroxide. The technical name is slaked lime. White, hygroscopic. It has an ionic structure Ca 2+ (OH -) 2. Decomposes on moderate heat. Absorbs moisture and carbon dioxide from the air. Slightly soluble in cold water (an alkaline solution is formed), even less so in boiling water. A clear solution (lime water) quickly becomes cloudy due to the precipitation of hydroxide (the suspension is called milk of lime). A qualitative reaction to the Ca 2+ ion is the passage of carbon dioxide through lime water with the appearance of a precipitate of CaCO 3 and its transition into solution. Reacts with acids and acid oxides, enters into ion exchange reactions. It is used in the production of glass, bleaching lime, lime mineral fertilizers, for causticizing soda and softening fresh water, as well as for preparing lime mortars - doughy mixtures (sand + slaked lime + water), serving as a binder for stone and brickwork, finishing (plastering) of walls and other building purposes. The hardening ("seizure") of such solutions is due to the absorption of carbon dioxide from the air.

Among all the elements of the periodic system, several can be distinguished, without which it is not only possible to develop various diseases in living organisms, but it is generally impossible to live and grow normally. One of these is calcium.

Interestingly, when it comes to this metal, as a simple substance, it does not have any benefit for a person, even harm. However, one has only to mention the Ca 2+ ions, as immediately there is a mass of points characterizing their importance.

Position of calcium in the periodic table

The characterization of calcium, like any other element, begins with an indication of its position in the periodic system. After all, it makes it possible to learn a lot about this atom:

nuclear charge;
the number of electrons and protons, neutrons;
oxidation state, higher and lower;
electronic configuration and other important things.

The element we are considering is located in the fourth large period of the second group, the main subgroup and has the serial number 20. Also, the chemical periodic table shows the atomic weight of calcium - 40.08, which is the average value of the existing isotopes of this atom.

The oxidation state is one, always constant, equal to +2. CaO formula. The Latin name for the element is calcium, hence the symbol for the atom Ca.

Characterization of calcium as a simple substance

Under normal conditions, this element is a metal, silvery-white in color. Calcium formula as a simple substance- Sa. Due to its high chemical activity, it is able to form many compounds belonging to different classes.

In the solid state of aggregation, it is not part of the human body, therefore it is important for industrial and technical needs (mainly chemical syntheses).

It is one of the most common metals in terms of its share in the earth's crust, about 1.5%. It belongs to the group of alkaline earths, since when dissolved in water it gives alkalis, but in nature it occurs in the form of multiple minerals and salts. A lot of calcium (400 mg/l) is included in sea water.

Crystal cell

The characteristic of calcium is explained by the structure of the crystal lattice, which can be of two types (since there is an alpha and a beta form):

cubic face-centric;
volume-centric.

The type of bond in the molecule is metallic, at the lattice sites, like all metals, there are atom-ions.

Being in nature

There are several basic substances in nature that contain this element.

Sea water.
Rocks and minerals.
Living organisms (shells and shells, bone tissue and so on).
Groundwater in the earth's crust.

The following types of rocks and minerals can be identified, which are natural sources of calcium.

Dolomite is a mixture of calcium and magnesium carbonate.
Fluorite is calcium fluoride.
Gypsum - CaSO 4 2H 2 O.
Calcite - chalk, limestone, marble - calcium carbonate.
Alabaster - CaSO 4 0.5H 2 O.
Apatity.

In total, about 350 different minerals and rocks that contain calcium are isolated.

How to get

For a long time, it was not possible to isolate the metal in a free form, since its chemical activity is high, you will not find it in nature in its pure form. Therefore, until the 19th century (1808), the element in question was another mystery that the periodic table carried.

Calcium as a metal was able to synthesize the English chemist Humphrey Davy. It was he who first discovered the features of the interaction of melts of solid minerals and salts with electric shock. To date, still the most relevant way to obtain this metal is the electrolysis of its salts, such as:

a mixture of calcium and potassium chlorides;
a mixture of fluoride and calcium chloride.

It is also possible to extract calcium from its oxide using the aluminothermic method common in metallurgy.

Physical Properties

The characterization of calcium in terms of physical parameters can be described in several points.

Aggregate state - under normal conditions, solid.
Melting point - 842 0 С.
The metal is soft and can be cut with a knife.
Color - silvery-white, brilliant.
It has good conductive and heat-conducting properties.
With prolonged heating, it passes into a liquid, then a vapor state, losing its metallic properties. Boiling point 1484 0 С.

The physical properties of calcium have one feature. When pressure is applied to a metal, at some point in time it loses its metallic properties and ability to conduct electricity. However, with a further increase in exposure, it is restored again and manifests itself as a superconductor, several times higher than the rest of the elements in terms of these indicators.

Chemical properties

The activity of this metal is very high. Therefore, there are many interactions in which calcium enters. Reactions with all non-metals are common for him, because as a reducing agent he is very strong.

Under normal conditions, it easily reacts with the formation of the corresponding binary compounds with: halogens, oxygen.
When heated: hydrogen, nitrogen, carbon, silicon, phosphorus, boron, sulfur and others.
On outdoors immediately interacts with carbon dioxide and oxygen, therefore it becomes covered with a gray coating.
Reacts violently with acids, sometimes with ignition.

Interesting properties of calcium are manifested when it comes to it in the composition of salts. So, beautiful caves growing on the ceiling and walls are nothing more than formed over time from water, carbon dioxide and bicarbonate under the influence of processes inside groundwater.

Considering how active the metal is in its normal state, it is stored in laboratories, like alkaline ones. In a dark glass container, with a tightly closed lid and under a layer of kerosene or paraffin.

A qualitative reaction to the calcium ion is the color of the flame in a beautiful, saturated brick-red color. It is also possible to identify a metal in the composition of compounds by insoluble precipitates of some of its salts (calcium carbonate, fluoride, sulfate, phosphate, silicate, sulfite).

metal connections

The types of metal compounds are as follows:

oxide;
hydroxide;
calcium salts (medium, acidic, basic, double, complex).

Calcium oxide known as CaO is used to create a building material (lime). If you extinguish the oxide with water, you get the corresponding hydroxide, which exhibits the properties of an alkali.

big practical value have exactly different calcium salts, which are used in different sectors of the economy. What kind of salts exist, we have already mentioned above. Let us give examples of the types of these compounds.

Medium salts - CaCO 3 carbonate, Ca 3 phosphate (PO 4) 2 and others.
Acidic - hydrosulfate CaHSO 4.
The main ones are bicarbonate (CaOH) 3 PO 4.
Complex - Cl 2.
Double - 5Ca (NO 3) 2 * NH 4 NO 3 * 10H 2 O.

It is in the form of compounds this class calcium is important for biological systems, since salts are the source of ions for the body.

Biological role

Why is calcium important for the human body? There are several reasons.

It is the ions of this element that are part of the intercellular substance and tissue fluid, participating in the regulation of the mechanisms of excitation, the production of hormones and neurotransmitters.
Calcium accumulates in the bones, tooth enamel in an amount of about 2.5% of the total body weight. This is quite a lot and plays an important role in strengthening these structures, maintaining their strength and stability. The growth of the body without it is impossible.
Blood clotting also depends on the ions in question.
It is part of the heart muscle, participating in its excitation and contraction.
It is a participant in the processes of exocytosis and other intracellular changes.

If the amount of calcium consumed is not enough, then the development of diseases such as:

rickets;
osteoporosis;
blood diseases.

The daily norm for an adult is 1000 mg, and for children from 9 years old 1300 mg. In order to prevent an overabundance of this element in the body, the indicated dose should not be exceeded. Otherwise, intestinal diseases may develop.

For all other living beings, calcium is no less important. For example, although many do not have a skeleton, the external means of strengthening them are also formations of this metal. Among them:

shellfish;
mussels and oysters;
sponges;
coral polyps.

All of them carry on their backs or, in principle, form in the process of life some kind of external skeleton that protects them from external influences and predators. Its main constituent is calcium salts.

Vertebrate animals, like humans, need these ions for normal growth and development and receive them with food.

There are many options with which it is possible to make up for the missing norm of the element in the body. Best of all, of course, natural methods - products containing the desired atom. However, if for some reason this is insufficient or impossible, the medical path is also acceptable.

So, the list of foods containing calcium is something like this:

dairy and sour-milk products;
fish;
greenery;
cereals (buckwheat, rice, whole grain flour pastries);
some citrus fruits (oranges, tangerines);
legumes;
all nuts (especially almonds and walnuts).

If you are allergic to some products or you can’t use them for another reason, then calcium-containing preparations will help to replenish the level of the desired element in the body.

All of them are salts of this metal, which have the ability to be easily absorbed by the body, quickly absorbed into the blood and intestines. Among them, the most popular and used are the following.

Calcium chloride - solution for injection or for oral administration to adults and children. It differs in the concentration of salt in the composition, it is used for "hot injections", because it causes just such a sensation when injected. There are forms with fruit juice to facilitate ingestion.
Available as tablets (0.25 or 0.5 g) and solutions for intravenous injection. Often in the form of tablets contains various fruit additives.
Calcium lactate - available in tablets of 0.5 g.

Natural calcium compounds (chalk, marble, limestone, gypsum) and their simplest processing products (lime) have been known to people since ancient times. In 1808, the English chemist Humphry Davy electrolyzed wet slaked lime (calcium hydroxide) with a mercury cathode and obtained calcium amalgam (calcium-mercury alloy). From this alloy, having driven away mercury, Davy obtained pure calcium.
He also proposed the name of a new chemical element, from the Latin "calx" denoting the name of limestone, chalk and other soft stones.

Being in nature and getting:

Calcium is the fifth most abundant element in the earth's crust (more than 3%), forms many rocks, many of which are based on calcium carbonate. Some of these rocks are of organic origin (shell rock), showing the important role of calcium in wildlife. Natural calcium is a mixture of 6 isotopes with mass numbers from 40 to 48, with 40 Ca accounting for 97% of the total. Other calcium isotopes have also been obtained by nuclear reactions, for example, radioactive 45 Ca.
To obtain a simple substance of calcium, electrolysis of melts of its salts or aluminothermy is used:
4CaO + 2Al \u003d Ca (AlO 2) 2 + 3Ca

Physical properties:

A silver-gray metal with a face-centered cubic lattice, much harder than the alkali metals. Melting point 842°C, boiling point 1484°C, density 1.55 g/cm 3 . At high pressures and temperatures, about 20 K passes into the state of a superconductor.

Chemical properties:

Calcium is not as active as the alkali metals, yet it must be stored under a layer of mineral oil or in tightly sealed metal drums. Already at ordinary temperature, it reacts with oxygen and nitrogen in the air, as well as with water vapor. When heated, it burns in air with a red-orange flame, forming oxide with an admixture of nitrides. Like magnesium, calcium continues to burn in an atmosphere of carbon dioxide. When heated, it reacts with other non-metals, forming compounds that are not always obvious in composition, for example:
Ca + 6B = CaB 6 or Ca + P => Ca 3 P 2 (also CaP or CaP 5)
In all its compounds, calcium has an oxidation state of +2.

The most important connections:

Calcium oxide CaO- ("quicklime") a white substance, an alkaline oxide, reacts vigorously with water ("extinguished") turning into hydroxide. Obtained by thermal decomposition of calcium carbonate.

Calcium hydroxide Ca(OH) 2- ("slaked lime") white powder, slightly soluble in water (0.16g/100g), strong alkali. A solution ("lime water") is used to detect carbon dioxide.

Calcium carbonate CaCO 3- the basis of most natural calcium minerals (chalk, marble, limestone, shell rock, calcite, Icelandic spar). In its pure form, the substance is white or colorless. crystals, When heated (900-1000 C) decomposes, forming calcium oxide. Not p-rim, reacts with acids, is able to dissolve in water saturated with carbon dioxide, turning into bicarbonate: CaCO 3 + CO 2 + H 2 O \u003d Ca (HCO 3) 2. The reverse process leads to the formation of calcium carbonate deposits, in particular formations such as stalactites and stalagmites.
It occurs in nature also in the composition of dolomite CaCO 3 *MgCO 3

Calcium sulfate CaSO 4- a white substance, in nature CaSO 4 * 2H 2 O ("gypsum", "selenite"). The latter, when heated carefully (180 C), passes into CaSO 4 * 0.5H 2 O ("burnt gypsum", "alabaster") - a white powder, when mixed with water, again forming CaSO 4 * 2H 2 O in the form of a solid, strong enough material. Slightly soluble in water, in excess of sulfuric acid it can dissolve, forming hydrosulfate.

Calcium phosphate Ca 3 (PO 4) 2- ("phosphorite"), insoluble, under the influence of strong acids passes into more soluble calcium hydro- and dihydrogen phosphates. Feedstock for the production of phosphorus, phosphoric acid, phosphate fertilizers. Calcium phosphates are also part of apatites, natural compounds with the approximate formula Ca 5 3 Y, where Y = F, Cl, or OH, respectively, fluorine, chlorine, or hydroxyapatite. Along with phosphorite, apatites are part of the bone skeleton of many living organisms, incl. and a person.

Calcium fluoride CaF 2 - (natural:"fluorite", "fluorspar"), insoluble in white. Natural minerals have a variety of colors due to impurities. Glows in the dark when heated and when exposed to UV radiation. Increases the fluidity ("fusibility") of slags in the production of metals, which is the reason for its use as a flux.

Calcium chloride CaCl 2- colorless crist. in-in well r-rimoe in water. Forms hydrated CaCl 2 *6H 2 O. Anhydrous ("fused") calcium chloride is a good drying agent.

Calcium nitrate Ca(NO 3) 2- ("calcium nitrate") colorless. crist. in-in well r-rimoe in water. Component pyrotechnic compositions, giving the flame a red-orange color.

Calcium carbide CaС 2- reacts with water, forming acetylene, for example: CaС 2 + H 2 O \u003d C 2 H 2 + Ca (OH) 2

Application:

Metallic calcium is used as a strong reducing agent in the production of some hard-to-recover metals ("calcium term"): chromium, rare earth elements, thorium, uranium, etc. In the metallurgy of copper, nickel, special steels and bronzes, calcium and its alloys are used to remove harmful impurities of sulfur, phosphorus, excess carbon.
Calcium is also used to bind small amounts of oxygen and nitrogen in the production of high vacuum and purification of inert gases.
Neutron-excess 48Ca ions are used for the synthesis of new chemical elements, for example element No. 114, . Another isotope of calcium, 45 Ca, is used as a radioactive tracer in studies of the biological role of calcium and its migration in the environment.

The main field of application of numerous calcium compounds is the production building materials(cement, building mixtures, drywall, etc.).

Calcium is one of the macronutrients in the composition of living organisms, forming compounds necessary for building both the internal skeleton of vertebrates and the external skeleton of many invertebrates, egg shells. Calcium ions are also involved in the regulation of intracellular processes, cause blood clotting. Lack of calcium in childhood leads to rickets, in the elderly - to osteoporosis. Dairy products, buckwheat, nuts serve as a source of calcium, and vitamin D contributes to its absorption. In case of calcium deficiency, various preparations are used: calcex, calcium chloride solution, calcium gluconate, etc.
The mass fraction of calcium in the human body is 1.4-1.7%, the daily requirement is 1-1.3 g (depending on age). Excess calcium intake can lead to hypercalcemia - the deposition of its compounds in the internal organs, the formation of blood clots in the blood vessels. Sources:
Calcium (element) // Wikipedia. URL: http://ru.wikipedia.org/wiki/Calcium (date of access: 3.01.2014).
Popular library of chemical elements: Calcium. // URL: http://n-t.ru/ri/ps/pb020.htm (3.01.2014).