EntranceCalcium (chemical element). Chemical and physical properties of calcium, its interaction with water Ca chemistry
CALCIUM (Latin Calcium), Ca, chemical element Group II of the short form (group 2 of the long form) of the periodic system; refers to alkaline earth metals; atomic number 20; atomic mass 40.078. There are 6 stable isotopes in nature: 40 Ca (96.941%), 42 Ca (0.647%), 43 Ca (0.135%), 44 Ca (2.086%), 46 Ca (0.004%), 48 Ca (0.187%); radioisotopes with mass numbers 34-54 were artificially obtained.
Historical reference. Many natural calcium compounds have been known in ancient times and were widely used in construction (for example, gypsum, lime, marble). Calcium metal was first isolated by G. Davy in 1808 during the electrolysis of a mixture of CaO and HgO oxides and the subsequent decomposition of the resulting calcium amalgam. The name comes from the Latin calx (genitive calcis) - lime, soft stone.
Prevalence in nature. Calcium content in earth's crust is 3.38% by weight. Due to high chemical activity, it is not found in a free state. The most common minerals are anorthite Ca, anhydrite CaSO 4, apatite Ca 5 (PO 4) 3 (F,Cl,OH), gypsum CaSO 4 2H 2 O, calcite and aragonite CaCO 3, perovskite CaTiO 3, fluorite CaF 2, scheelite CaWO 4 . Calcium minerals are found in sedimentary (such as limestone), igneous, and metamorphic rocks. Calcium compounds are found in living organisms: they are the main components of vertebrate bone tissue (hydroxyapatite, fluorapatite), coral skeletons, mollusk shells (calcium carbonate and phosphates), etc. The presence of Ca 2+ ions determines water hardness.
Properties. The configuration of the outer electron shell of the calcium atom is 4s 2; in compounds it exhibits an oxidation state of +2, rarely +1; Pauling electronegativity 1.00, atomic radius 180 pm, radius of Ca 2+ ion 114 pm (coordination number 6). calcium is a silvery-white soft metal; up to 443 °C the modification with a cubic face-centered crystal lattice is stable, above 443 °C - with a cubic body-centered lattice; melting point 842°C, boiling point 1484°C, density 1550 kg/m 3 ; thermal conductivity 125.6 W/(m K).
Calcium is a metal of high chemical activity (stored in hermetically sealed containers or under a layer of mineral oil). At normal conditions easily interacts with oxygen (calcium oxide CaO is formed), when heated - with hydrogen (CaH 2 hydride), halogens (calcium halides), boron (CaB 6 boride), carbon (calcium carbide CaC 2), silicon (silicides Ca 2 Si, CaSi, CaSi 2, Ca 3 Si 4), nitrogen (nitride Ca 3 N 2), phosphorus (phosphides Ca 3 P 2, CaP, CaP 5), chalcogens (chalcogenides of the composition CaX, where X is S, Se, Te). Calcium interacts with other metals (Li, Cu, Ag, Au, Mg, Zn, Al, Pb, Sn, etc.) to form intermetallic compounds. Calcium metal reacts with water to form calcium hydroxide Ca(OH) 2 and H 2 . Reacts vigorously with most acids, forming the corresponding salts (for example, calcium nitrate, calcium sulfate, calcium phosphates). Dissolves in liquid ammonia to form a dark blue solution with metallic conductivity. When ammonia evaporates from such a solution, ammonia is released. Gradually, calcium reacts with ammonia to form the amide Ca(NH 2) 2. Forms various complex compounds, the most important are complexes with oxygen-containing polydentate ligands, for example Ca complexonates.
Biological role. Calcium is a biogenic element. The daily human need for calcium is about 1 g. In living organisms, calcium ions are involved in the processes of muscle contraction and transmission of nerve impulses.
Receipt. Calcium metal is produced by electrolytic and metallothermic methods. The electrolytic method is based on the electrolysis of molten calcium chloride with a touch cathode or a liquid copper-calcium cathode. Calcium is distilled off from the resulting copper-calcium alloy at a temperature of 1000-1080 °C and a pressure of 13-20 kPa. The metallothermic method is based on the reduction of calcium from its oxide with aluminum or silicon at 1100-1200 °C. This produces calcium aluminate or silicate, as well as calcium gas, which is then condensed. World production of calcium compounds and materials containing calcium is about 1 billion tons/year (1998).
Application. Calcium is used as a reducing agent in the production of many metals (Rb, Cs, Zr, Hf, V, etc.). Calcium silicides, as well as alloys of calcium with sodium, zinc and other metals, are used as deoxidizers and desulfurizers of some alloys and oil, to purify argon from oxygen and nitrogen, and in electric vacuum devices as a gas absorber. CaCl 2 chloride is used as a desiccant in chemical synthesis, gypsum is used in medicine. Calcium silicates are the main components of cement.
Lit.: Rodyakin V.V. Calcium, its compounds and alloys. M., 1967; Spitsyn V. I., Martynenko L. I. Inorganic chemistry. M., 1994. Part 2; Inorganic chemistry / Edited by Yu. D. Tretyakov. M., 2004. T. 2.
L. N. Komissarova, M. A. Ryumin.
Calcium
CALCIUM-I; m.[from lat. calx (calcis) - lime] Chemical element (Ca), a silver-white metal that is part of limestone, marble, etc.
◁ Calcium, oh, oh. K salts.
calcium(lat. Calcium), a chemical element of group II of the periodic table, 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 ordinary temperatures it is easily oxidized in air. In terms of prevalence in the earth's crust, it ranks 5th (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 part of antifriction materials. Calcium compounds are used in construction (lime, cement), calcium preparations are used in medicine.
CALCIUMCALCIUM (lat. Calcium), Ca (read “calcium”), a chemical element with atomic number 20, is located in the fourth period in group IIA of Mendeleev’s periodic system of elements; atomic mass 40.08. Belongs to the alkaline earth elements (cm. ALKALINE EARTH METALS).
Natural calcium consists of a mixture of nuclides (cm. NUCLIDE) with mass numbers of 40 (in a mixture by mass of 96.94%), 44 (2.09%), 42 (0.667%), 48 (0.187%), 43 (0.135%) and 46 (0.003%). Outer electron layer 4 configuration s 2
. In almost all compounds, the oxidation state of calcium is +2 (valence 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 coordination number 6) up to 0.148 nm (for coordination number 12). The energies of sequential ionization of a neutral calcium atom are, respectively, 6.133, 11.872, 50.91, 67.27 and 84.5 eV. According to the Pauling scale, the electronegativity of calcium is about 1.0. In its free form, calcium is a silvery-white metal.
History of discovery
Calcium compounds are found everywhere in nature, so humanity has been familiar with them since ancient times. Lime has long been used in construction (cm. LIME)(quicklime and slaked), which has long been considered a simple substance, “earth.” However, in 1808 the English scientist G. Davy (cm. DAVY Humphrey) managed to obtain 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 the Latin calx, genus calcis - lime). In Russia for some time this metal was called “liming”.
Being in nature
Calcium is one of the most common elements on Earth. It accounts for 3.38% of the mass of the earth's crust (5th most abundant after oxygen, silicon, aluminum and iron). Due to its high chemical activity, calcium does not occur in free form in nature. Most calcium is found in silicates (cm. SILICATES) and aluminosilicates (cm. ALUMINUM SILICATES) various rocks (granites (cm. GRANITE), gneisses (cm. GNEISS) and so on.). In the form of sedimentary rocks, calcium compounds are represented by chalk and limestones, consisting mainly of the mineral calcite (cm. CALCITE)(CaCO 3). The crystalline form of calcite - marble - is much less common in nature.
Calcium minerals such as limestone are quite common (cm. LIMESTONE) CaCO3, anhydrite (cm. ANHYDRITE) CaSO 4 and gypsum (cm. GYPSUM) CaSO 4 2H 2 O, fluorite (cm. FLUORITE) CaF 2, apatites (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 found in living organisms. Thus, hydroxyapatite Ca 5 (PO 4) 3 (OH), or, in another entry, 3Ca 3 (PO 4) 2 ·Ca(OH) 2, is the basis of the bone tissue of vertebrates, including humans; The shells and shells of many invertebrates, eggshells, etc. are made from calcium carbonate CaCO 3.
Receipt
Metallic calcium 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 (parameter a = 0.558 nm) is stable; b-Ca with a cubic body-centered lattice of the a-Fe type (parameter a = 0.448 nm) is more stable. Melting point of calcium is 839 °C, boiling point is 1484 °C, density is 1.55 g/cm3.
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, which is why 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 = Ca(OH) 2 + H 2.
Calcium reacts with active non-metals (oxygen, chlorine, bromine) under normal conditions:
2Ca + O 2 = 2CaO; Ca + Br 2 = CaBr 2.
When heated in air or oxygen, calcium ignites. Calcium reacts with less active non-metals (hydrogen, boron, carbon, silicon, nitrogen, phosphorus and others) when heated, for example:
Ca + H 2 = CaH 2 (calcium hydride),
Ca + 6B = CaB 6 (calcium boride),
3Ca + N 2 = Ca 3 N 2 (calcium nitride)
Ca + 2C = CaC 2 (calcium carbide)
3Ca + 2P = Ca 3 P 2 (calcium phosphide), calcium phosphides of the compositions CaP and CaP 5 are also known;
2Ca + Si = Ca 2 Si (calcium silicide); calcium silicides of the compositions CaSi, Ca 3 Si 4 and CaSi 2 are also known.
The occurrence 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 = Ca(OH) 2 + 2H 2,
Ca 3 N 2 + 3H 2 O = 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 = 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 = Ca(OH) 2.
Ca(OH)2 obtained in this way is usually called slaked lime or milk of lime (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 acidic oxides, CaO forms salts, for example:
CaO + CO 2 = CaCO 3; CaO + SO 3 = 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. Insoluble in water are fluoride CaF 2, carbonate CaCO 3, sulfate CaSO 4, average orthophosphate Ca 3 (PO 4) 2, oxalate CaC 2 O 4 and some others.
It is important that, unlike the average calcium carbonate CaCO 3, acidic calcium carbonate (bicarbonate) Ca(HCO 3) 2 is soluble in water. In nature, this leads to the following processes. When cold rain or river water, saturated with carbon dioxide, penetrates underground and falls on limestone, their dissolution is observed:
CaCO 3 + CO 2 + H 2 O = Ca(HCO 3) 2.
In the same places where water saturated with calcium bicarbonate comes to the surface of the earth and is heated by the sun's rays, a reverse reaction occurs:
Ca(HCO 3) 2 = CaCO 3 + CO 2 + H 2 O.
This is how large masses of substances are transferred in nature. As a result, huge holes can form underground (see Karst (cm. KARST (natural phenomenon))), and beautiful stone “icicles” - stalactites - form in the caves (cm. STALACTITES (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 boils, bicarbonate decomposes and CaCO 3 precipitates. This phenomenon leads, for example, to the fact that scale forms in the kettle over time.
Application of calcium and its compounds
Calcium metal 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-shaped crystals of calcite CaCO3 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 - is an excellent finishing material. Chalk is used for whitewashing. Large quantities of limestone are consumed in the production of cast iron, as they allow the transfer of refractory impurities iron ore(for example, quartz SiO 2) into relatively low-melting slags.
Bleach is very effective as a disinfectant. (cm. BLEACHING POWDER)- “bleach” Ca(OCl)Cl - mixed chloride and calcium hypochloride (cm. CALCIUM HYPOCHLORITE), with high oxidizing ability.
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 dihydrate sulfate - gypsum CaSO 4 ·2H 2 O. Gypsum is widely used in construction, in sculpture, for the manufacture of stucco molding and various artistic products. Plaster is also used in medicine to fix bones during fractures.
Calcium chloride CaCl 2 is used along with table salt to combat icing of road surfaces. 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. An important component of the mineral metabolism of animals and humans and the mineral nutrition of plants, calcium performs various functions in the body. Composed of apatite (cm. APATITE), as well as sulfate and carbonate, calcium forms the mineral component of bone tissue. The human body weighing 70 kg contains about 1 kg of calcium. Calcium participates in the functioning of ion channels (cm. ION CHANNELS) that carry out the transport of substances through biological membranes, in transmission nerve impulse (cm. NERVOUS IMPULSE), in blood clotting processes (cm. BLOOD CLOTTING) 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), calcinosis (cm. CALCINOSIS) etc. Therefore, human food must contain calcium compounds in the required 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 viscous metal. Specific gravity 1.6. Dictionary of foreign words included in the Russian language. Pavlenkov F., 1907. CALCIUM (new Latin calcium, from Latin calx lime). Silver colored metal. Dictionary of foreign words,... ... Dictionary of foreign words of the Russian language
CALCIUM- CALCIUM, Calcium, chemical. element, symbol Ca, shiny, silvery-white crystalline metal. fracture, belonging to the group of alkaline earth metals. Ud. weight 1.53; at. V. 40.07; melting point 808°. Sa is one of the very... Big medical encyclopedia
- (Calcium), Ca, chemical element of group II of the periodic system, atomic number 20, atomic mass 40.08; refers to alkaline earth metals; melting point 842shC. Contained in the bone tissue of vertebrates, mollusk shells, and eggshells. Calcium... ... Modern encyclopedia
The metal is silvery-white, viscous, malleable, and quickly oxidizes in air. Melting rate pa 800-810°. Found in nature in the form of various salts that form deposits of chalk, limestone, marble, phosphorites, apatites, gypsum, etc. dor... ... Technical railway dictionary
- (Latin Calcium) Ca, a chemical element of group II of the periodic table, atomic number 20, atomic mass 40.078, belongs to the alkaline earth metals. Name from Latin calx, genitive calcis lime. Silvery white metal,... ... Big Encyclopedic Dictionary
Natural calcium compounds (chalk, marble, limestone, gypsum) and the products of their simplest processing (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 (an alloy of calcium and mercury). From this alloy, having distilled off 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.
Finding in nature and obtaining:
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 living nature. Natural calcium is a mixture of 6 isotopes with mass numbers from 40 to 48, with 40 Ca accounting for 97% of the total. Nuclear reactions have also produced other isotopes of calcium, for example radioactive 45 Ca.
To obtain a simple calcium substance, electrolysis of molten calcium salts or aluminothermy is used:
4CaO + 2Al = Ca(AlO 2) 2 + 3Ca
Physical properties:
A silver-gray metal with a cubic face-centered lattice, much harder than the alkali metals. Melting point 842°C, boiling point 1484°C, density 1.55 g/cm3. At high pressures and temperatures of about 20 K it goes into the superconductor state.
Chemical properties:
Calcium is not as active as alkali metals, but it must be stored under a layer of mineral oil or in tightly sealed metal drums. Already at normal temperatures 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 an oxide with an admixture of nitrides. Like magnesium, calcium continues to burn in the atmosphere 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, which reacts vigorously with water ("quenched") turning into a 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, Iceland 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 = Ca(HCO 3) 2. Reverse process leads to the appearance of calcium carbonate deposits, in particular formations such as stalactites and stalagmites
It is also found in nature as part 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 carefully heated (180 C), turns into CaSO 4 *0.5H 2 O (“burnt gypsum”, “alabaster”) - a white powder, which, when mixed with water, again forms CaSO 4 *2H 2 O in the form of a solid, quite durable material. Slightly soluble in water, it can dissolve in excess sulfuric acid, forming hydrogen sulfate.
Calcium phosphate Ca 3 (PO 4) 2- (“phosphorite”), insoluble, under the influence of strong acids it turns into more soluble calcium hydro- and dihydrogen phosphates. Feedstock for the production of phosphorus, phosphoric acid, phosphate fertilizers. Calcium phosphates are also included in 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 man.
Calcium fluoride CaF 2 - (natural:"fluorite", "fluorspar"), an insoluble substance of white color. Natural minerals have a variety of colors due to impurities. Glows in the dark when heated and under UV irradiation. It increases the fluidity (“fusibility”) of slags when producing metals, which explains its use as a flux.
Calcium chloride CaCl 2- colorless christ. It is well soluble in water. Forms crystalline hydrate CaCl 2 *6H 2 O. Anhydrous ("fused") calcium chloride is a good desiccant.
Calcium nitrate Ca(NO 3) 2- ("calcium nitrate") colorless. christ. It is well soluble in water. An integral part of pyrotechnic compositions that gives the flame a red-orange color.
Calcium carbide CaС 2- reacts with water, forming acetylene, for example: CaС 2 + H 2 O = С 2 H 2 + Ca(OH) 2
Application:
Metallic calcium is used as a strong reducing agent in the production of some difficult-to-reduce metals (“calciothermy”): 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 when obtaining high vacuum and purifying inert gases.
Neutron-excess 48 Ca ions are used for the synthesis of new chemical elements, for example element No. 114, . Another calcium isotope, 45Ca, is used as a radioactive tracer in research biological role calcium and its migration in the environment.
The main area of application for numerous calcium compounds is the production of building materials (cement, building mixtures, plasterboard, etc.).
Calcium is one of the macroelements in living organisms, forming compounds necessary for the construction of both the internal skeleton of vertebrates and the external skeleton of many invertebrates, the shell of eggs. Calcium ions also participate in the regulation of intracellular processes and determine blood clotting. Lack of calcium in childhood leads to rickets, and in the elderly - to osteoporosis. The source of calcium is dairy products, buckwheat, nuts, and its absorption is facilitated by vitamin D. If there is a lack of calcium, various drugs 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). Excessive calcium intake can lead to hypercalcemia - the deposition of its compounds in internal organs, the formation of blood clots in blood vessels. Sources:
Calcium (element) // Wikipedia. URL: http://ru.wikipedia.org/wiki/Calcium (access date: 01/3/2014).
Popular library of chemical elements: Calcium. // URL: http://n-t.ru/ri/ps/pb020.htm (01/3/2014).
Home / Lectures 1st year / General and organic chemistry / Question 23. Calcium / 2. Physical and chemical properties
Physical properties. Calcium is a silver-white malleable metal that melts at a temperature of 850 degrees. C and boils at 1482 degrees. C. It is significantly harder than alkali metals.
Chemical properties. Calcium is an active metal. So, under normal conditions, it easily interacts with atmospheric oxygen and halogens:
2 Ca + O2 = 2 CaO (calcium oxide);
Ca + Br2 = CaBr2 (calcium bromide).
Calcium reacts with hydrogen, nitrogen, sulfur, phosphorus, carbon and other non-metals when heated:
Ca + H2 = CaH2 (calcium hydride);
3 Ca + N2 = Ca3N2 (calcium nitride);
Ca + S = CaS (calcium sulfide);
3 Ca + 2 P = Ca3P2 (calcium phosphide);
Ca + 2 C = CaC2 (calcium carbide).
Calcium reacts slowly with cold water, but very vigorously with hot water:
Ca + 2 H2O = Ca(OH)2 + H2.
Calcium can remove oxygen or halogens from oxides and halides less active metals, i.e. it has restorative properties:
5 Ca + Nb2O5 = CaO + 2 Nb;
- 1. Being in nature
- 3. Receipt
- 4. Application
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Calcium | directory Pesticides.ru
For many people, knowledge about calcium is limited only to the fact that this element is necessary for healthy bones and teeth. Where else it is contained, why it is needed and how necessary it is, not everyone has an idea. However, calcium is found in many familiar compounds, both natural and man-made. Chalk and lime, stalactites and stalagmites of caves, ancient fossils and cement, gypsum and alabaster, dairy products and anti-osteoporosis drugs - all this and much more is high in calcium.
This element was first obtained by G. Davy in 1808, and at first it was not particularly actively used. However, this metal is now the fifth most produced in the world, and the need for it is increasing year by year. The main area of use of calcium is the production of building materials and mixtures. However, it is necessary to build not only houses, but also living cells. In the human body, calcium is part of the skeleton, makes muscle contractions possible, ensures blood clotting, regulates the activity of a number of digestive enzymes and performs other quite numerous functions. It is no less important for other living objects: animals, plants, fungi and even bacteria. At the same time, the need for calcium is quite high, which makes it possible to classify it as a macronutrient.
Calcium, Ca is a chemical element of the main subgroup of group II of the Mendeleev periodic system. Atomic number – 20. Atomic mass – 40.08.
Calcium is an alkaline earth metal. When free, malleable, fairly hard, white. By density it belongs to light metals.
- Density – 1.54 g/cm3,
- Melting point – +842 °C,
- Boiling point – +1495 °C.
Calcium has pronounced metallic properties. In all compounds the oxidation state is +2.
In air it becomes covered with a layer of oxide, and when heated it burns with a reddish, bright flame. It reacts slowly with cold water, but quickly displaces hydrogen from hot water and forms hydroxide. When interacting with hydrogen, it forms hydrides. At room temperature it reacts with nitrogen, forming nitrides. It also easily combines with halogens and sulfur, and reduces metal oxides when heated.
Calcium is one of the most abundant elements in nature. In the earth's crust its content is 3% of the mass. It occurs in the form of deposits of chalk, limestone, and marble (a natural type of calcium carbonate CaCO3). There are large quantities of deposits of gypsum (CaSO4 x 2h3O), phosphorite (Ca3(PO4)2 and various calcium-containing silicates.
Water
. Calcium salts are almost always present in natural water. Of these, only gypsum is slightly soluble in it. When water contains carbon dioxide, calcium carbonate goes into solution in the form of bicarbonate Ca(HCO3)2.Hard water
. Natural water with a large amount of calcium or magnesium salts is called hard water.Soft water
. When the content of these salts is low or absent, the water is called soft.Soils
. As a rule, soils are sufficiently provided with calcium. And, since calcium is contained in greater mass in the vegetative part of plants, its removal with the harvest is insignificant.Loss of calcium from the soil occurs as a result of its leaching by precipitation. This process depends on the granulometric composition of the soil, the amount of precipitation, the type of plants, the forms and doses of lime and mineral fertilizers. Depending on these factors, calcium losses from the arable layer range from several tens to 200 – 400 kg/ha or more.
Calcium content in different types of soils
Podzolic soils contain 0.73% (of soil dry matter) calcium.
Gray forest – 0.90% calcium.
Chernozems – 1.44% calcium.
Serozems – 6.04% calcium.
In the plant, calcium is found in the form of phosphates, sulfates, carbonates, and in the form of salts of pectic and oxalic acids. Almost up to 65% of calcium in plants can be extracted with water. The rest is treated with weak vinegar and hydrochloric acids. Most calcium is found in aging cells.
Symptoms of calcium deficiency according to: |
|
Culture | Symptoms of deficiency |
General symptoms | Whitening of the apical bud; Whitening of young leaves; The tips of the leaves are curved down; The edges of the leaves curl upward; |
Potato | The upper leaves bloom poorly; The growing point of the stem dies; There is a light stripe at the edges of the leaves, which later darkens; The edges of the leaves are curled upward; |
White and cauliflower cabbage | The leaves of young plants have chlorotic spotting (marbling) or white stripes along the edges; In old plants, leaves curl and burns appear on them; The growing point dies off |
The terminal lobes of leaves die off Flowers fall; A dark spot appears on the fruit in the apical part, which increases as the fruit grows (tomato blossom end rot) |
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The apical buds die off; The edges of young leaves are curled up, have a ragged appearance, and subsequently die off; The upper parts of the shoots die off; Damage to root tips; There are brown spots in the fruit pulp (bitter pitting); The taste of the fruit deteriorates; Marketability of fruits decreases |
Functions of calcium
The effect of this element on plants is multifaceted and, as a rule, positive. Calcium:
- Strengthens metabolism;
- Plays an important role in the movement of carbohydrates;
- Affects the metamorphosis of nitrogenous substances;
- Accelerates the consumption of reserve proteins of seeds during germination;
- Plays a role in the process of photosynthesis;
- a strong antagonist of other cations, preventing their excess entry into plant tissues;
- Affects the physicochemical properties of protoplasm (viscosity, permeability, etc.), and therefore the normal course of biochemical processes in the plant;
- Calcium compounds with pectin substances glue the walls of individual cells together;
- Affects enzyme activity.
It should be noted that the influence of calcium compounds (lime) on enzyme activity is expressed not only in direct action, but also due to the improvement physical and chemical properties soil and its nutritional regime. In addition, liming the soil significantly affects the processes of vitamin biosynthesis.
Lack (deficiency) of calcium in plants
Lack of calcium primarily affects the development of the root system. The formation of root hairs on the roots stops. The outer root cells are destroyed.
This symptom manifests itself both with a lack of calcium and with an imbalance in the nutrient solution, that is, the predominance of monovalent cations of sodium, potassium and hydrogen in it.
In addition, the presence of nitrate nitrogen in the soil solution increases the supply of calcium to plant tissues, and reduces the supply of ammonia.
Signs of calcium starvation are expected when the calcium content is less than 20% of the cation exchange capacity of the soil.
Symptoms Visually, calcium deficiency is determined by the following signs:
- The roots of plants have damaged tips with a brown color;
- The growing point becomes deformed and dies;
- Flowers, ovaries and buds fall off;
- The fruits are damaged by necrosis;
- The leaves are noted to be chlorotic;
- The apical bud dies and stem growth stops.
Cabbage, alfalfa, and clover are highly sensitive to the presence of calcium. It has been established that these same plants are also characterized by increased sensitivity to soil acidity.
Mineral calcium poisoning results in interveinal chlorosis with whitish necrotic spots. They may be colored or have concentric rings filled with water. Some plants respond to excess calcium by growing leaf rosettes, dying shoots and dropping leaves. The symptoms are similar in appearance to iron and magnesium deficiency.
The source of calcium replenishment in the soil is lime fertilizers. They are divided into three groups:
- Hard calcareous rocks;
- Soft calcareous rocks;
- Industrial waste with high lime content.
Based on the content of CaO and MgO, hard calcareous rocks are divided into:
- limestones (55–56% CaO and up to 0.9% MgO);
- dolomitized limestones (42–55% CaO and up to 9% MgO);
- dolomites (32–30% CaO and 18–20% MgO).
Limestones
– basic lime fertilizers. Contains 75–100% Ca and Mg oxides calculated as CaCO3.Dolomitized limestone
. Contains 79–100% active substance (a.i.) calculated as CaCO3. Recommended in crop rotations with potatoes, legumes, flax, root crops, as well as on highly podzolized soils.Marl
. Contains up to 25–15% CaCO3 and impurities in the form of clay and sand up to 20–40%. Acts slowly. Recommended for use on light soils.Chalk
. Contains 90–100% CaCO3. The action is faster than that of limestone. It is a valuable lime fertilizer in finely ground form.Burnt lime
(CaO). The CaCO3 content is over 70%. It is characterized as a strong and fast acting liming material.Slaked lime
(Ca(OH)2). CaCO3 content – 35% or more. It is also a strong and fast acting lime fertilizer.Dolomite flour
. The content of CaCO3 and MgCO3 is about 100%. Its action is slower than that of calcareous tuffs. Typically used where magnesium is required.Calcareous tuffs
. Content of CaCO3 – 15–96%, impurities – up to 25% clay and sand, 0.1% P2O5. The action is faster than that of limestone.Defecation dirt (defecation)
. Consists of CaCO3 and Ca(OH)2. The lime content of CaO is up to 40%. Nitrogen is also present - 0.5% and P2O5 - 1-2%. This is waste from beet sugar factories. It is recommended for use not only to reduce soil acidity, but also in beet growing areas on chernozem soils.Shale ash cyclones
. Dry dusty material. The content of the active substance is 60–70%. Refers to industrial waste.Dust from furnaces and cement factories
. The CaCO3 content must exceed 60%. In practice, it is used in farms located in close proximity to cement plants.Metallurgical slags
. Used in the regions of the Urals and Siberia. Non-hygroscopic, easy to spray. Must contain at least 80% CaCO3 and have a moisture content of no more than 2%. The granulometric composition is important: 70% - less than 0.25 mm, 90% - less than 0.5 mm.Organic fertilizers. The Ca content in terms of CaCO3 is 0.32–0.40%.
Phosphorite flour. Calcium content – 22% CaCO3.
Lime fertilizers are used not only to provide soil and plants with calcium. the main objective their use is liming of soils. This is a method of chemical reclamation. It is aimed at neutralizing excess soil acidity, improving its agrophysical, agrochemical and biological properties, supplying plants with magnesium and calcium, mobilizing and immobilizing macroelements and microelements, creating optimal water-physical, physical, air conditions for the life of cultivated plants.
Efficiency of soil liming
Simultaneously with satisfying the needs of plants for calcium as an element of mineral nutrition, liming leads to multiple positive changes in soils.
The effect of liming on the properties of some soils
Calcium promotes the coagulation of soil colloids and prevents their leaching. This leads to easier tillage and improved aeration.
As a result of liming:
- sandy humus soils increase their water absorption capacity;
- On heavy clay soils, soil aggregates and clumping are formed, which improve water permeability.
In particular, they neutralize organic acids and H-ions are displaced from the absorbing complex. This leads to the elimination of metabolic acidity and a decrease in hydrolytic acidity of the soil. At the same time, an improvement in the cationic composition of the soil absorption complex is observed, which occurs due to the replacement of hydrogen and aluminum ions with calcium and magnesium cations. This increases the degree of soil saturation with bases and increases the absorption capacity.
The effect of liming on the supply of nitrogen to plants
After liming, the positive agrochemical properties of the soil and its structure can be maintained for several years. This helps create favorable conditions for enhancing beneficial microbiological processes for the mobilization of nutrients. The activity of ammonifiers, nitrifiers, and nitrogen-fixing bacteria that live freely in the soil increases.
Liming helps to increase the proliferation of nodule bacteria and improve the supply of nitrogen to the host plant. It has been established that bacterial fertilizers lose their effectiveness on acidic soils.
The effect of liming on the supply of ash elements to plants
Liming helps supply the plant with ash elements, since it increases the activity of bacteria that decompose organic phosphorus compounds in the soil and promote the transition of iron and aluminum phosphates into calcium phosphate salts available to plants. Liming of acidic soils enhances microbiological and biochemical processes, which, in turn, increases the amount of nitrates, as well as digestible forms of phosphorus and potassium.
Effect of liming on the forms and availability of macroelements and microelements
Liming increases the amount of calcium, and when using dolomite flour - magnesium. At the same time, toxic forms of manganese and aluminum become insoluble and pass into the precipitated form. The availability of elements such as iron, copper, zinc, manganese is decreasing. Nitrogen, sulfur, potassium, calcium, magnesium, phosphorus and molybdenum become more available.
The influence of liming on the action of physiologically acidic fertilizers
Liming increases the effectiveness of physiologically acidic mineral fertilizers, especially ammonia and potash.
The positive effect of physiologically acidic fertilizers without the addition of lime fades, and over time can turn negative. So, in fertilized areas, yields are even less than in unfertilized areas. The combination of liming with the use of fertilizers increases their effectiveness by 25–50%.
When liming, enzymatic processes in the soil are activated, by which its fertility is indirectly judged.
Compiled by: Grigorovskaya P.I.
Page added: 05.12.13 00:40
Last update: 05/22/14 16:25
Literary sources:
Glinka N.L. General chemistry. Textbook for universities. Publisher: Leningrad: Chemistry, 1985, p. 731
Mineev V.G. Agrochemistry: Textbook. – 2nd edition, revised and expanded. – M.: Moscow State University Publishing House, KolosS Publishing House, 2004. – 720 p., l. ill.: ill. – (Classical university textbook).
Petrov B.A., Seliverstov N.F. Mineral nutrition of plants. A reference guide for students and gardeners. Ekaterinburg, 1998. 79 p.
Encyclopedia for children. Volume 17. Chemistry. / Head. ed. V.A. Volodin. – M.: Avanta +, 2000. – 640 p., ill.
Yagodin B.A., Zhukov Yu.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodina. – M.: Kolos, 2002. – 584 pp.: illus (Textbooks and teaching aids for higher education students educational institutions).
Images (reworked):
20 Ca Calcium, licensed under CC BY
Calcium deficiency in wheat, by CIMMYT, licensed under CC BY-NC-SA
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Calcium and its role for humanity - Chemistry
Calcium and its role for humanity
Introduction
Being in nature
Receipt
Physical properties
Chemical properties
Application of calcium compounds
Biological role
Conclusion
Bibliography
Introduction
Calcium is an element of the main subgroup of the second group, the fourth period of the periodic system of chemical elements of D.I. Mendeleev, with atomic number 20. It is designated by the symbol Ca (lat. Calcium). The simple substance calcium (CAS number: 7440-70-2) is a soft, reactive alkaline earth metal of a silvery-white color.
Despite the ubiquity of element No. 20, even chemists have not all seen elemental calcium. But this metal, both in appearance and in behavior, is completely different from alkali metals, contact with which is fraught with the danger of fires and burns. It can be safely stored in air; it does not ignite from water. The mechanical properties of elemental calcium do not make it a “black sheep” in the family of metals: calcium surpasses many of them in strength and hardness; it can be turned on a lathe, drawn into wire, forged, pressed.
And yet, elemental calcium is almost never used as a structural material. He's too active for that. Calcium easily reacts with oxygen, sulfur, and halogens. Even with nitrogen and hydrogen, under certain conditions, it reacts. The environment of carbon oxides, inert for most metals, is aggressive for calcium. It burns in an atmosphere of CO and CO2.
History and origin of the name
The name of the element comes from Lat. calx (in genitive case calcis) - “lime”, “soft stone”. It was proposed by the English chemist Humphry Davy, who isolated calcium metal by the electrolytic method in 1808. Davy electrolyzed a mixture of wet slaked lime and mercuric oxide HgO on a platinum plate, which served as the anode. The cathode was a platinum wire immersed in liquid mercury. As a result of electrolysis, calcium amalgam was obtained. Having distilled mercury from it, Davy obtained a metal called calcium.
Calcium compounds - limestone, marble, gypsum (as well as lime - a product of calcination of limestone) have been used in construction for several thousand years ago. Until the end of the 18th century, chemists considered lime to be a simple solid. In 1789, A. Lavoisier suggested that lime, magnesia, barite, alumina and silica are complex substances.
Being in nature
Due to its high chemical activity, calcium does not occur in free form in nature.
Calcium accounts for 3.38% of the mass of the earth's crust (5th most abundant after oxygen, silicon, aluminum and iron).
Isotopes. Calcium occurs in nature as a mixture of six isotopes: 40Ca, 42Ca, 43Ca, 44Ca, 46Ca and 48Ca, among which the most common - 40Ca - is 96.97%.
Of the six natural isotopes of calcium, five are stable. The sixth isotope, 48Ca, the heaviest of the six and very rare (its isotopic abundance is only 0.187%), was recently discovered to undergo double beta decay with a half-life of 5.3 x 1019 years.
In rocks and minerals. Most of the calcium is contained in silicates and aluminosilicates of various rocks (granites, gneisses, etc.), especially in feldspar - Ca anorthite.
In the form of sedimentary rocks, calcium compounds are represented by chalk and limestones, consisting mainly of the mineral calcite (CaCO3). The crystalline form of calcite - marble - is much less common in nature.
Calcium minerals such as calcite CaCO3, anhydrite CaSO4, alabaster CaSO4 0.5h3O and gypsum CaSO4 2h3O, fluorite CaF2, apatite Ca5(PO4)3(F,Cl,OH), dolomite MgCO3 CaCO3 are quite widespread. The presence of calcium and magnesium salts in natural water determines its hardness.
Calcium, vigorously migrating in the earth's crust and accumulating in various geochemical systems, forms 385 minerals (the fourth largest number of minerals).
Migration in the earth's crust. In the natural migration of calcium significant role plays the “carbonate equilibrium” associated with reversible reaction interaction of calcium carbonate with water and carbon dioxide to form soluble bicarbonate:
CaCO3 + h3O + CO2 - Ca (HCO3)2 - Ca2+ + 2HCO3-
(equilibrium shifts to the left or right depending on the concentration of carbon dioxide).
Biogenic migration. In the biosphere, calcium compounds are found in almost all animal and plant tissues (see also below). A significant amount of calcium is found in living organisms. Thus, hydroxyapatite Ca5(PO4)3OH, or, in another entry, 3Ca3(PO4)2·Ca(OH)2, is the basis of the bone tissue of vertebrates, including humans; The shells and shells of many invertebrates, eggshells, etc. are made of calcium carbonate CaCO3. In living tissues of humans and animals there is 1.4-2% Ca (by mass fraction); in a human body weighing 70 kg, the calcium content is about 1.7 kg (mainly in the intercellular substance of bone tissue).
Receipt
Free metallic calcium is obtained by electrolysis of a melt consisting of CaCl2 (75-80%) and KCl or from CaCl2 and CaF2, as well as aluminothermic reduction of CaO at 1170-1200 °C:
4CaO + 2Al = CaAl2O4 + 3Ca.
Physical properties
Calcium metal exists in two allotropic modifications. Up to 443 °C, ?-Ca with a cubic face-centered lattice (parameter a = 0.558 nm) is stable; higher stable is ?-Ca with a cubic body-centered lattice of the ?-Fe type (parameter a = 0.448 nm). Standard enthalpy?H0 transition? > ? is 0.93 kJ/mol.
Chemical properties
Calcium is a typical alkaline earth metal. 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, which is why 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 or liquid paraffin.
In the series of standard potentials, calcium is located to the left of hydrogen. The standard electrode potential of the Ca2+/Ca0 pair is ? 2.84 V, so that calcium actively reacts with water, but without ignition:
Ca + 2H2O = Ca(OH)2 + H2^ + Q.
Calcium reacts with active non-metals (oxygen, chlorine, bromine) under normal conditions:
2Ca + O2 = 2CaO, Ca + Br2 = CaBr2.
When heated in air or oxygen, calcium ignites. Calcium reacts with less active non-metals (hydrogen, boron, carbon, silicon, nitrogen, phosphorus and others) when heated, for example:
Ca + H2 = CaH2, Ca + 6B = CaB6,
3Ca + N2 = Ca3N2, Ca + 2C = CaC2,
3Ca + 2P = Ca3P2 (
calcium phosphide), calcium phosphides of the compositions CaP and CaP5 are also known;
2Ca + Si = Ca2Si
(calcium silicide), calcium silicides of the compositions CaSi, Ca3Si4 and CaSi2 are also known.
The occurrence of the above reactions, as a rule, is accompanied by the release of a large amount of heat (that is, 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:
CaH2 + 2H2O = Ca(OH)2 + 2H2^,
Ca3N2 + 3H2O = 3Ca(OH)2 + 2Nh4^.
The Ca2+ ion is colorless. When soluble calcium salts are added to the flame, the flame turns brick-red.
Calcium salts such as CaCl2 chloride, CaBr2 bromide, CaI2 iodide and Ca(NO3)2 nitrate are highly soluble in water. Insoluble in water are fluoride CaF2, carbonate CaCO3, sulfate CaSO4, orthophosphate Ca3(PO4)2, oxalate CaC2O4 and some others.
It is important that, unlike calcium carbonate CaCO3, acidic calcium carbonate (bicarbonate) Ca(HCO3)2 is soluble in water. In nature, this leads to the following processes. When cold rain or river water, saturated with carbon dioxide, penetrates underground and falls on limestone, their dissolution is observed:
CaCO3 + CO2 + H2O = Ca(HCO3)2.
In the same places where water saturated with calcium bicarbonate comes to the surface of the earth and is heated by the sun's rays, a reverse reaction occurs:
Ca(HCO3)2 = CaCO3 + CO2^ + H2O.
This is how large masses of substances are transferred in nature. As a result, huge gaps can form underground, and beautiful stone “icicles” - stalactites and stalagmites - form in caves.
The presence of dissolved calcium bicarbonate in water largely determines the temporary hardness of water. It is called temporary because when water boils, bicarbonate decomposes and CaCO3 precipitates. This phenomenon leads, for example, to the fact that scale forms in the kettle over time.
Applications of calcium metal
The main use of calcium metal is as a reducing agent in the production of metals, especially nickel, copper and stainless steel. Calcium and its hydride are also used to produce difficult-to-reduce metals such as chromium, thorium and uranium. Calcium-lead alloys are used in batteries and bearing alloys. Calcium granules are also used to remove traces of air from vacuum devices.
Metallothermy
Pure metallic calcium is widely used in metallothermy for the production of rare metals.
Alloying of alloys
Pure calcium is used to alloy lead used for the production of battery plates and maintenance-free starter lead-acid batteries with low self-discharge. Also, metallic calcium is used for the production of high-quality calcium babbits BKA.
Nuclear fusion
The 48Ca isotope is the most effective and commonly used material for the production of superheavy elements and the discovery of new elements on the periodic table. For example, in the case of using 48Ca ions to produce superheavy elements in accelerators, the nuclei of these elements are formed hundreds and thousands of times more efficiently than when using other “projectiles” (ions).
Application of calcium compounds
Calcium hydride. By heating calcium in a hydrogen atmosphere, Cah3 (calcium hydride) is obtained, which is used in metallurgy (metallothermy) and in the production of hydrogen in the field.
Optical and laser materials. Calcium fluoride (fluorite) is used in the form of single crystals in optics (astronomical objectives, lenses, prisms) and as a laser material. Calcium tungstate (scheelite) in the form of single crystals is used in laser technology and also as a scintillator.
Calcium carbide. Calcium carbide CaC2 is widely used for the production of acetylene and for the reduction of metals, as well as in the production of calcium cyanamide (by heating calcium carbide in nitrogen at 1200 °C, the reaction is exothermic, carried out in cyanamide furnaces).
Chemical current sources. Calcium, as well as its alloys with aluminum and magnesium, are used in backup thermal electric batteries as an anode (for example, calcium-chromate element). Calcium chromate is used in such batteries as a cathode. The peculiarity of such batteries is an extremely long shelf life (decades) in a suitable condition, the ability to operate in any conditions (space, high pressure), high specific energy by weight and volume. Disadvantage: short lifespan. Such batteries are used where it is necessary to create colossal electrical power for a short period of time (ballistic missiles, some spacecraft, etc.).
Fireproof materials. Calcium oxide, both in free form and as part of ceramic mixtures, is used in the production of refractory materials.
Medicines. Calcium compounds are widely used as an antihistamine.
Calcium chloride
Calcium gluconate
Calcium glycerophosphate
In addition, calcium compounds are included in drugs for the prevention of osteoporosis, in vitamin complexes for pregnant women and the elderly.
Biological role
Calcium is a common macronutrient in the body of plants, animals and humans. In humans and other vertebrates, most of it is contained in the skeleton and teeth in the form of phosphates. From various forms Calcium carbonate (lime) consists of the skeletons of most groups of invertebrates (sponges, coral polyps, mollusks, etc.). Calcium ions are involved in blood clotting processes, as well as in ensuring constant osmotic pressure of the blood. Calcium ions also serve as one of the universal second messengers and regulate a variety of intracellular processes - muscle contraction, exocytosis, including the secretion of hormones and neurotransmitters, etc. The calcium concentration in the cytoplasm of human cells is about 10?7 mol, in intercellular fluids about 10 ?3 mol.
Calcium requirements depend on age. For adults, the required daily intake is from 800 to 1000 milligrams (mg), and for children from 600 to 900 mg, which is very important for children due to the intensive growth of the skeleton. Most of the calcium that enters the human body with food is found in dairy products; the remaining calcium comes from meat, fish, and some plant products (especially legumes). Absorption occurs in both the large and small intestines and is facilitated by an acidic environment, vitamin D and vitamin C, lactose, and unsaturated fatty acids. The role of magnesium in calcium metabolism is important; with its deficiency, calcium is “washed out” from the bones and deposited in the kidneys (kidney stones) and muscles.
Aspirin, oxalic acid, and estrogen derivatives interfere with the absorption of calcium. When combined with oxalic acid, calcium produces water-insoluble compounds that are components of kidney stones.
Due to the large number of processes associated with it, the calcium content in the blood is precisely regulated, and with proper nutrition, a deficiency does not occur. Prolonged absence from the diet can cause cramps, joint pain, drowsiness, growth defects, and constipation. Deeper deficiency leads to constant muscle cramps and osteoporosis. Abuse of coffee and alcohol can cause calcium deficiency, since some of it is excreted in the urine.
Excessive doses of calcium and vitamin D can cause hypercalcemia, followed by intense calcification of bones and tissues (mainly affecting the urinary system). Long-term excess disrupts the functioning of muscle and nerve tissues, increases blood clotting and reduces the absorption of zinc by bone cells. The maximum daily safe dose for an adult is 1500 to 1800 milligrams.
Products Calcium, mg/100 g
Sesame 783
Nettle 713
Forest mallow 505
Large plantain 412
Galinsoga 372
Sardines in oil 330
Ivy budra 289
Dog rose 257
Almond 252
Plantain lanceolist. 248
Hazelnut 226
Amaranth seed 214
Watercress 214
Soybeans dry 201
Children under 3 years old - 600 mg.
Children from 4 to 10 years old - 800 mg.
Children from 10 to 13 years old - 1000 mg.
Adolescents from 13 to 16 years old - 1200 mg.
Youth 16 and older - 1000 mg.
Adults from 25 to 50 years old - from 800 to 1200 mg.
Pregnant and breastfeeding women - from 1500 to 2000 mg.
Conclusion
Calcium is one of the most abundant elements on Earth. There is a lot of it in nature: mountain ranges and clay rocks are formed from calcium salts, it is found in sea and river water, and is part of plant and animal organisms.
Calcium constantly surrounds city dwellers: almost all main building materials - concrete, glass, brick, cement, lime - contain this element in significant quantities.
Naturally, having such chemical properties, calcium cannot exist in nature in a free state. But calcium compounds - both natural and artificial - have acquired paramount importance.
Bibliography
1. Editorial Board: Knunyants I. L. (chief editor) Chemical Encyclopedia: in 5 volumes - Moscow: Soviet encyclopedia, 1990. - T. 2. - P. 293. - 671 p.
2. Doronin. N.A. Calcium, Goskhimizdat, 1962. 191 pp. with illustrations.
3. Dotsenko VA. - Therapeutic and preventive nutrition. - Question. nutrition, 2001 - N1-p.21-25
4. Bilezikian J. P. Calcium and bone metabolism // In: K. L. Becker, ed.
www.e-ng.ru
World of Science
Calcium is a metal element of the main subgroup II of group 4 of the periodic table of chemical elements. It belongs to the alkaline earth metal family. The outer energy level of the calcium atom contains 2 paired s-electrons
Which he is able to energetically give away during chemical interactions. Thus, Calcium is a reducing agent and in its compounds has an oxidation state of +2. In nature, calcium is found only in the form of salts. The mass fraction of calcium in the earth's crust is 3.6%. The main natural calcium mineral is calcite CaCO3 and its varieties - limestone, chalk, marble. There are also living organisms (for example, corals), the backbone of which consists mainly of calcium carbonate. Also important calcium minerals are dolomite CaCO3 MgCO3, fluorite CaF2, gypsum CaSO4 2h3O, apatite, feldspar, etc. Calcium plays an important role in the life of living organisms. Mass fraction of calcium in human body is 1.4-2%. It is part of teeth, bones, other tissues and organs, participates in the process of blood clotting, and stimulates cardiac activity. To provide the body with a sufficient amount of calcium, you should definitely consume milk and dairy products, green vegetables, and fish. The simple substance calcium is a typical silver-white metal. It is quite hard, plastic, has a density of 1.54 g/cm3 and a melting point of 842? C. Chemically, calcium is very active. Under normal conditions, it easily interacts with oxygen and moisture in the air, so it is stored in hermetically sealed containers. When heated in air, calcium ignites and forms an oxide: 2Ca + O2 = 2CaO. Calcium reacts with chlorine and bromine when heated, and with fluorine even in the cold. The products of these reactions are the corresponding halides, for example: Ca + Cl2 = CaCl2. When calcium is heated with sulfur, calcium sulfide is formed: Ca + S = CaS. Calcium can also react with other non-metals. Interaction with water leads to the formation of slightly soluble calcium hydroxide and the release of hydrogen gas :Ca + 2h3O = Ca (OH) 2 + h3. Calcium metal is widely used. It is used as a rosette in the production of steels and alloys, and as a reducing agent for the production of some refractory metals.
Calcium is obtained by electrolysis of molten calcium chloride. Thus, calcium was first obtained in 1808 by Humphry Davy.
worldofscience.ru
Among all the elements of the periodic table, several can be identified, without which not only do various diseases develop in living organisms, but it is generally impossible to live and grow normally. One of these is calcium.
It is interesting that when we talk about this metal as a simple substance, it has no benefit for humans, even harm. However, as soon as you mention Ca 2+ ions, a lot of points immediately arise that characterize their importance.
Position of calcium in the periodic table
The characterization of calcium, like any other element, begins with indicating its location in the periodic table. After all, it makes it possible to learn a lot about a given atom:
- nuclear charge;
- number of electrons and protons, neutrons;
- oxidation state, highest and lowest;
- electronic configuration and other important things.
The element we are considering is located in the fourth major period of the second group, the main subgroup, and has a serial number of 20. Also, the periodic chemical table shows the atomic weight of calcium - 40.08, which is the average value of the existing isotopes of a given atom.
The oxidation state is one, always constant, equal to +2. Formula CaO. The Latin name for the element is calcium, hence the symbol for the Ca atom.
Characteristics of calcium as a simple substance
Under normal conditions, this element is a metal, silvery-white in color. The formula of calcium as a simple substance is Ca. Due to its high chemical activity, it is capable of forming many compounds belonging to different classes.
In a 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 the earth’s crust, about 1.5%. It belongs to the alkaline earth group, since when dissolved in water it produces alkalis, but in nature it is found in the form of multiple minerals and salts. A lot of calcium (400 mg/l) is included in sea water.
Crystal cell
The characteristics of calcium are explained by the structure of the crystal lattice, which can be of two types (since there is an alpha and beta form):
- cubic face-centric;
- volume-centric.
The type of bond in the molecule is metallic; at lattice sites, like all metals, there are atom ions.
Being in nature
There are several main substances in nature that contain this element.
- Sea water.
- Rocks and minerals.
- Living organisms (shells and shells, bone tissue, etc.).
- Groundwater in the earth's crust.
The following types of rocks and minerals can be identified as 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, there are about 350 different minerals and rocks that contain calcium.
Methods of obtaining
For a long time it was not possible to isolate the metal in its free form, since its chemical activity is high and cannot be found in nature in its pure form. Therefore, until the 19th century (1808), the element in question was another mystery posed by the periodic table.
The English chemist Humphry Davy managed to synthesize calcium as a metal. It was he who first discovered the peculiarities of the interaction of melts of solid minerals and salts with electric shock. Today, 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 aluminothermy, a common method in metallurgy.
Physical properties
The characteristics of calcium according to physical parameters can be described in several points.
- The state of aggregation is solid under normal conditions.
- Melting point - 842 0 C.
- The metal is soft and can be cut with a knife.
- Color - silver-white, shiny.
- It has good conductive and heat-conducting properties.
- When heated for a long time, it turns into a liquid, then a vapor state, losing metallic properties. Boiling point 1484 0 C.
The physical properties of calcium have one peculiarity. When pressure is applied to a metal, at some point in time it loses its metallic properties and ability to conduct electrically. However, with a further increase in exposure, it is restored again and manifests itself as a superconductor, several times higher in these indicators than other elements.
Chemical properties
The activity of this metal is very high. Therefore, there are many interactions that calcium enters into. Reactions with all non-metals are common for him, because as a reducing agent he is very strong.
- Under normal conditions, it easily reacts to form the corresponding binary compounds with: halogens, oxygen.
- When heated: hydrogen, nitrogen, carbon, silicon, phosphorus, boron, sulfur and others.
- In the open air it immediately interacts with carbon dioxide and oxygen, and therefore becomes covered with a gray coating.
- Reacts violently with acids, sometimes causing inflammation.
Interesting properties of calcium appear when it comes to 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 within underground waters.
Considering how active the metal is in its normal state, it is stored in laboratories, just like alkaline metals. In a dark glass container, with a tightly closed lid and under a layer of kerosene or paraffin.
A qualitative reaction to calcium ion is the coloring of the flame in a beautiful, rich brick-red color. You can also identify the metal in the composition of the compounds by the 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 building material(lime). If you quench the oxide with water, you get the corresponding hydroxide, which exhibits the properties of an alkali.
Various calcium salts, which are used in different sectors of the economy, are of great practical importance. We have already mentioned above what kind of salts exist. Let us give examples of the types of these connections.
- Medium salts - carbonate CaCO 3, phosphate Ca 3 (PO 4) 2 and others.
- Acidic - hydrogen sulfate 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 of this class that 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 excitation mechanisms, the production of hormones and neurotransmitters.
- Calcium accumulates in bones and 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 this 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 diseases such as:
- rickets;
- osteoporosis;
- blood diseases.
The daily intake for an adult is 1000 mg, and for children over 9 years old 1300 mg. In order to prevent an excess of this element in the body, you should not exceed the specified dose. Otherwise, intestinal diseases may develop.
For all other living beings, calcium is no less important. For example, although many do not have a skeleton, their external means of strengthening are also formations of this metal. Among them:
- shellfish;
- mussels and oysters;
- sponges;
- coral polyps.
They all carry on their backs or, in principle, form in the process of life a certain external skeleton that protects them from external influences and predators. Main component its - calcium salts.
Vertebrates, like humans, need these ions for normal growth and development and receive them from food.
There are many options with which it is possible to replenish the missing element in the body. The best, of course, are natural methods - products containing the desired atom. However, if for some reason this is insufficient or impossible, the medical route is also acceptable.
So, the list of foods containing calcium is something like this:
- dairy and fermented milk products;
- fish;
- greenery;
- grains (buckwheat, rice, baked goods made from whole grain flour);
- some citrus fruits (oranges, tangerines);
- legumes;
- all nuts (especially almonds and walnuts).
If you are allergic to some foods or cannot eat them for another reason, then calcium-containing preparations will help replenish the level of the necessary 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”, since it causes exactly this sensation when injected. There are forms with fruit juice for easier oral administration.
- Available in both tablets (0.25 or 0.5 g) and solutions for intravenous injections. Often in tablet form it contains various fruit additives.
- Calcium lactate - available in tablets of 0.5 g.