Calcium in the periodic system. Properties and uses of calcium. Chemical properties of calcium

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

At normal conditions this element is a metal, silver- white color. The formula of calcium as a simple substance is Ca. Due to its high chemical activity, it is able to form many compounds belonging to different classes.

in solid state of aggregation 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.

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

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

1. Dolomite is a mixture of calcium and magnesium carbonate.
2. Fluorite is calcium fluoride.
3. Gypsum - CaSO 4 2H 2 O.
4. Calcite - chalk, limestone, marble - calcium carbonate.
5. Alabaster - CaSO 4 0.5H 2 O.
6. 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, so far the most actual way obtaining 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.

1. Aggregate state - under normal conditions, solid.
2. Melting point - 842 0 С.
3. The metal is soft and can be cut with a knife.
4. Color - silvery-white, brilliant.
5. It has good conductive and heat-conducting properties.
6. 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.

1. Under normal conditions, it easily reacts with the formation of the corresponding binary compounds with: halogens, oxygen.
2. When heated: hydrogen, nitrogen, carbon, silicon, phosphorus, boron, sulfur and others.
3. In the open air, it immediately interacts with carbon dioxide and oxygen, therefore it becomes covered with a gray coating.
4. 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.

It is the various calcium salts that are used in various sectors of the economy that are of great practical importance. What kind of salts exist, we have already mentioned above. Let us give examples of the types of these compounds.

1. Medium salts - CaCO 3 carbonate, Ca 3 phosphate (PO 4) 2 and others.
2. Acidic - hydrosulfate CaHSO 4.
3. The main ones are bicarbonate (CaOH) 3 PO 4.
4. Complex - Cl 2.
5. 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.

1. 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.
2. Calcium accumulates in bones, tooth enamel in an amount of about 2.5% of total weight body. 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.
3. Blood clotting also depends on the ions in question.
4. It is part of the heart muscle, participating in its excitation and contraction.
5. 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. Main component its 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.

1. 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.
2. Available as tablets (0.25 or 0.5 g) and solutions for intravenous injection. Often in the form of tablets contains various fruit additives.
3. Calcium lactate - available in tablets of 0.5 g.

Calcium(Calcium), Ca, a chemical element of group II of the periodic system of Mendeleev, atomic number 20, atomic mass 40.08; silver-white light metal. The natural element is a mixture of six stable isotopes: 40 Ca, 42 Ca, 43 Ca, 44 Ca, 46 Ca and 48 Ca, of which 40 Ca is the most abundant (96.97%).

Ca compounds - limestone, marble, gypsum (as well as lime - a product of burning limestone) have been used in construction since ancient times. Until the end of the 18th century, chemists considered lime to be a simple substance. In 1789, A. Lavoisier suggested that lime, magnesia, barite, alumina and silica are complex substances. In 1808, G. Davy, subjecting a mixture of wet slaked lime with mercury oxide to electrolysis with a mercury cathode, prepared an amalgam of Ca, and after driving mercury out of it, he obtained a metal called "Calcium" (from Latin calx, genus case calcis - lime) .

Distribution of calcium in nature. In terms of abundance in the earth's crust, Ca occupies the 5th place (after O, Si, Al, and Fe); content 2.96% by weight. It migrates vigorously and accumulates in various geochemical systems, forming 385 minerals (4th place in terms of the number of minerals). There is little Ca in the Earth's mantle and, probably, even less in the Earth's core (0.02% in iron meteorites). Ca predominates in the lower part of the earth's crust, accumulating in basic rocks; most of Ca is enclosed in feldspar - anorthite Ca; content in basic rocks 6.72%, in acidic (granites and others) 1.58%. An exceptionally sharp differentiation of Ca occurs in the biosphere, mainly associated with the "carbonate equilibrium": when carbon dioxide interacts with CaCO 3 carbonate, soluble bicarbonate Ca (HCO 3) 2 is formed: CaCO 3 + H 2 O + CO 2 \u003d Ca (HCO 3) 2 \u003d Ca 2+ + 2HCO 3-. This reaction is reversible and is the basis of Ca redistribution. With a high content of CO 2 in the waters, Ca is in solution, and with a low content of CO 2, the mineral calcite CaCO 3 precipitates, forming powerful deposits of limestone, chalk, and marble.

Biogenic migration also plays a huge role in the history of Ca. In living matter from elements-metals, Ca is the main one. Organisms are known that contain more than 10% Ca (more carbon), building their skeleton from Ca compounds, mainly from CaCO 3 (calcareous algae, many molluscs, echinoderms, corals, rhizomes, etc.). With the burial of the skeletons of the sea. animals and plants is associated with the accumulation of colossal masses of algal, coral and other limestones, which, plunging into the depths of the earth and mineralizing, turn into different kinds marble.

Vast areas with a humid climate (forest zones, tundra) are characterized by a deficiency of Ca - here it is easily leached from the soil. This is associated with low soil fertility, low productivity of domestic animals, their small size, and often skeletal diseases. Therefore, liming of soils, feeding domestic animals and birds, etc. is of great importance. On the contrary, CaCO 3 is sparingly soluble in a dry climate, therefore steppe and desert landscapes are rich in Ca. Gypsum CaSO 4 2H 2 O often accumulates in salt marshes and salt lakes.

Rivers bring a lot of Ca into the ocean, but it does not linger in ocean water (average content is 0.04%), but is concentrated in the skeletons of organisms and, after their death, is deposited on the bottom mainly in the form of CaCO 3 . Lime silts are widespread on the bottom of all oceans at depths of no more than 4000 m (CaCO 3 dissolves at great depths, organisms there often experience a deficiency of Ca).

Groundwater plays an important role in Ca migration. In limestone massifs, they vigorously leach CaCO 3 in places, which is associated with the development of karst, the formation of caves, stalactites and stalagmites. In addition to calcite, in the seas of past geological epochs, the deposition of Ca phosphates (for example, the Karatau phosphorite deposits in Kazakhstan), dolomite CaCO 3 ·MgCO 3, and gypsum during evaporation were widespread in the seas of past geological epochs.

In the course of geological history, biogenic carbonate formation increased, while the chemical precipitation of calcite decreased. In the Precambrian seas (over 600 million years ago) there were no animals with a calcareous skeleton; they have become widespread since the Cambrian (corals, sponges, etc.). This is attributed to the high content of CO 2 in the Precambrian atmosphere.

Physical properties of calcium. The crystal lattice of the α-form of Ca (stable at ordinary temperature) is face-centered cubic, a = 5.56Å. Atomic radius 1.97Å, ionic radius Ca 2+ 1.04Å. Density 1.54 g/cm3 (20 °C). Above 464 °C, the hexagonal β-form is stable. t pl 851 °C, t kip 1482 °C; temperature coefficient of linear expansion 22 10 -6 (0-300 °C); thermal conductivity at 20 °C 125.6 W/(m K) or 0.3 cal/(cm s °C); specific heat capacity (0-100 °C) 623.9 j/(kg K) or 0.149 cal/(g °C); electrical resistivity at 20 °C 4.6 10 -8 ohm m or 4.6 10 -6 ohm cm; temperature coefficient of electrical resistance 4.57 10 -3 (20 °C). Modulus of elasticity 26 Gn / m 2 (2600 kgf / mm 2); tensile strength 60 MN / m 2 (6 kgf / mm 2); elastic limit 4 MN / m 2 (0.4 kgf / mm 2), yield strength 38 MN / m 2 (3.8 kgf / mm 2); elongation 50%; Brinell hardness 200-300 MN / m 2 (20-30 kgf / mm 2). Calcium of sufficiently high purity is plastic, well pressed, rolled and can be machined.

Chemical properties of calcium. The configuration of the outer electron shell of the Ca 4s 2 atom, according to which Ca in compounds is 2-valent. Chemically Ca is very active. At ordinary temperatures, Ca easily interacts with oxygen and moisture in the air, so it is stored in hermetically sealed vessels or under mineral oil. When heated in air or oxygen, it ignites, giving the basic oxide CaO. Peroxides Ca-CaO 2 and CaO 4 are also known. WITH cold water Ca reacts quickly at first, then the reaction slows down due to the formation of a Ca(OH) 2 film. Ca interacts vigorously with hot water and acids, releasing H 2 (except for concentrated HNO 3). It reacts with fluorine in the cold, and with chlorine and bromine - above 400 ° C, giving CaF 2, CaCl 2 and CaBr 2, respectively. These halides in the molten state form with Ca the so-called subcompounds - CaF, CaCl, in which Ca is formally monovalent. When Ca is heated with sulfur, calcium sulfide CaS is obtained, the latter adds sulfur, forming polysulfides (CaS 2, CaS 4 and others). Interacting with dry hydrogen at 300-400 ° C, Ca forms a hydride CaH 2 - an ionic compound in which hydrogen is an anion. At 500 °C Ca and nitrogen give Ca 3 N 2 nitride; the interaction of Ca with ammonia in the cold leads to the complex ammonia Ca 6 . When heated without access to air with graphite, silicon or phosphorus, Ca gives calcium carbide CaC 2 , silicides Ca 2 Si, CaSi, CaSi 2 and phosphide Ca 3 P 2 , respectively. Ca forms intermetallic compounds with Al, Ag, Au, Cu, Li, Mg, Pb, Sn and others.

Getting Calcium. In industry, Ca is obtained in two ways: 1) by heating a briquetted mixture of CaO and Al powder at 1200 ° C in a vacuum of 0.01-0.02 mm Hg. Art.; released by the reaction: 6CaO + 2 Al \u003d 3CaO Al 2 O 3 + 3Ca Ca vapor condenses on a cold surface; 2) by electrolysis of a melt of CaCl 2 and KCl with a liquid copper-calcium cathode, an alloy of Cu - Ca (65% Ca) is prepared, from which Ca is distilled off at a temperature of 950-1000 ° C in a vacuum of 0.1-0.001 mm Hg. Art.

The use of calcium. In the form of a pure metal, Ca is used as a reducing agent for U, Th, Cr, V, Zr, Cs, Rb and some rare earth metals from their compounds. It is also used for the deoxidation of steels, bronzes and other alloys, for the removal of sulfur from petroleum products, for the dehydration of organic liquids, for the purification of argon from nitrogen impurities, and as a gas absorber in electric vacuum devices. Antifriction materials of the Pb-Na-Ca system, as well as Pb-Ca alloys, which are used for the manufacture of electrical shells, have received great application in technology. cables. Alloy Ca-Si-Ca (silicocalcium) is used as a deoxidizer and degasser in the production of high-quality steels.

calcium in the body. Ca is one of the biogenic elements necessary for the normal course of life processes. It is present in all tissues and fluids of animals and plants. Only rare organisms can develop in an environment devoid of Ca. In some organisms, the Ca content reaches 38%; in humans - 1.4-2%. Cells of plant and animal organisms need strictly defined ratios of Ca 2+ , Na + and K + ions in extracellular media. Plants get Ca from the soil. According to their relationship to Ca, plants are divided into calcephiles and calcephobes. Animals get Ca from food and water. Ca is necessary for the formation of a number of cellular structures, maintaining the normal permeability of outer cell membranes, for fertilizing the eggs of fish and other animals, and for activating a number of enzymes. Ca 2+ ions transmit excitation to the muscle fiber, causing it to contract, increase the strength of heart contractions, increase the phagocytic function of leukocytes, activate the system of protective blood proteins, and participate in its coagulation. In cells, almost all Ca is in the form of compounds with proteins, nucleic acids, phospholipids, in complexes with inorganic phosphates and organic acids. In the blood plasma of humans and higher animals, only 20-40% Ca can be associated with proteins. In animals with a skeleton, up to 97-99% of all Ca is used as a building material: in invertebrates, mainly in the form of CaCO 3 (mollusk shells, corals), in vertebrates, in the form of phosphates. Many invertebrates store Ca before molting to build a new skeleton or to provide vital functions in adverse conditions.

The content of Ca in the blood of humans and higher animals is regulated by the hormones of the parathyroid and thyroid glands. Vitamin D plays the most important role in these processes. Ca absorption occurs in the anterior part of the small intestine. Assimilation of Ca worsens with a decrease in acidity in the intestine and depends on the ratio of Ca, P and fat in food. The optimal Ca / P ratio in cow's milk is about 1.3 (in potatoes 0.15, in beans 0.13, in meat 0.016). With an excess of P or oxalic acid in food, Ca absorption deteriorates. Bile acids accelerate its absorption. The optimal Ca/fat ratio in human food is 0.04-0.08 g of Ca per 1 g of fat. Excretion of Ca occurs mainly through the intestines. Mammals during lactation lose a lot of Ca with milk. With violations of phosphorus-calcium metabolism in young animals and children, rickets develop, in adult animals - a change in the composition and structure of the skeleton (osteomalacia).

Calcium compounds- limestone, marble, gypsum (as well as lime - a product of limestone) have been used in construction since ancient times. Until the end of the 18th century, chemists considered lime to be a simple substance. In 1789, A. Lavoisier suggested that lime, magnesia, barite, alumina and silica are complex substances. In 1808, Davy, by subjecting a mixture of wet slaked lime with mercury oxide to electrolysis with a mercury cathode, prepared a calcium amalgam, and after driving mercury out of it, he obtained a metal called "calcium" (from lat. Calx, genus. case calcis - lime).

Arrangement of electrons in orbits.

+20Ca… |3s 3p 3d | 4s

Calcium is called an alkaline earth metal, it is classified as an S element. At the external electronic level, calcium has two electrons, so it gives compounds: CaO, Ca (OH) 2, CaCl2, CaSO4, CaCO3, etc. Calcium belongs to typical metals - it has a high affinity for oxygen, restores almost all metals from their oxides, and forms a rather strong base Ca (OH) 2.

The crystal lattices of metals can be various types, however, calcium is characterized by a face-centered cubic lattice.

The sizes, shape and mutual arrangement of crystals in metals are emitted by metallographic methods. The most complete assessment of the metal structure in this respect is given by microscopic analysis of its thin section. A sample is cut out of the metal under test, and its plane is ground, polished and etched with a special solution (etchant). As a result of etching, the structure of the sample is highlighted, which is examined or photographed using a metallographic microscope.

Calcium is a light metal (d = 1.55), silver-white in color. It is harder and melts at a higher temperature (851°C) than sodium, which is next to it in the periodic table. This is because there are two electrons per calcium ion in the metal. Therefore, the chemical bond between ions and electron gas is stronger than that of sodium. In chemical reactions, calcium valence electrons are transferred to atoms of other elements. In this case, doubly charged ions are formed.

Calcium is highly reactive with metals, especially with oxygen. In air, it oxidizes more slowly than alkali metals, since the oxide film on it is less permeable to oxygen. When heated, calcium burns with the release of huge amounts of heat:

Calcium reacts with water, displacing hydrogen from it and forming a base:

Ca + 2H2O = Ca(OH)2 + H2

Owing to its great reactivity with oxygen, calcium finds some use in obtaining rare metals from their oxides. Metal oxides are heated together with calcium chips; as a result of the reactions, calcium oxide and a metal are obtained. The use of calcium and some of its alloys for the so-called deoxidation of metals is based on the same property. Calcium is added to molten metal and it removes traces of dissolved oxygen; the resulting calcium oxide floats to the surface of the metal. Calcium is part of some alloys.

Calcium is obtained by electrolysis of molten calcium chloride or by the aluminothermic method. Calcium oxide, or slaked lime, is a white powder that melts at 2570°C. It is obtained by calcining limestone:

CaCO3 \u003d CaO + CO2 ^

Calcium oxide is a basic oxide, so it reacts with acids and acid anhydrides. With water, it gives a base - calcium hydroxide:

CaO + H2O = Ca(OH)2

The addition of water to calcium oxide, called lime slaking, proceeds with the release of a large amount of heat. Part of the water is converted into steam. Calcium hydroxide, or slaked lime, is a white substance, slightly soluble in water. An aqueous solution of calcium hydroxide is called lime water. Such a solution has rather strong alkaline properties, since calcium hydroxide dissociates well:

Ca (OH) 2 \u003d Ca + 2OH

Compared to hydrates of alkali metal oxides, calcium hydroxide is a weaker base. This is explained by the fact that the calcium ion is doubly charged and more strongly attracts hydroxyl groups.

Hydrated lime and its solution, called lime water, react with acids and acid anhydrides, including carbon dioxide. Lime water is used in laboratories to discover carbon dioxide, since the resulting insoluble calcium carbonate causes the water to become cloudy:

Ca + 2OH + CO2 = CaCO3v + H2O

However, when carbon dioxide is passed for a long time, the solution becomes transparent again. This is due to the fact that calcium carbonate is converted into a soluble salt - calcium bicarbonate:

CaCO3 + CO2 + H2O = Ca(HCO3)2

In industry, calcium is obtained in two ways:

By heating a briquetted mixture of CaO and Al powder at 1200 ° C in a vacuum of 0.01 - 0.02 mm. rt. Art.; released by the reaction:

6CaO + 2Al = 3CaO Al2O3 + 3Ca

Calcium vapor condenses on a cold surface.

By electrolysis of a melt of CaCl2 and KCl with a liquid copper-calcium cathode, an alloy of Cu - Ca (65% Ca) is prepared, from which calcium is distilled off at a temperature of 950 - 1000 ° C in a vacuum of 0.1 - 0.001 mm Hg.

A method has also been developed for obtaining calcium by thermal dissociation of calcium carbide CaC2.

Calcium is one of the most abundant elements in nature. It contains approximately 3% (mass) in the earth's crust. Calcium salts form in nature large accumulations in the form of carbonates (chalk, marble), sulfates (gypsum), phosphates (phosphorites). Under the action of water and carbon dioxide, carbonates pass into solution in the form of hydrocarbons and are transported by underground and river waters long distances. When calcium salts are washed out, caves can form. Due to the evaporation of water or an increase in temperature, deposits of calcium carbonate can form in a new place. So, for example, stalactites and stalagmites are formed in caves.

Soluble calcium and magnesium salts determine the overall hardness of water. If they are present in water in small quantities, then the water is called soft. With a high content of these salts (100 - 200 mg of calcium salts - in 1 liter in terms of ions), water is considered hard. In such water, soap foams poorly, since calcium and magnesium salts form insoluble compounds with it. Doesn't work well in hard water food products, and when boiled, it gives scale on the walls of steam boilers. Scale does not conduct heat well, causes an increase in fuel consumption and accelerates the wear of the boiler walls. Scale formation is a complex process. When heated, the acid salts of calcium and magnesium carbonic acid decompose and turn into insoluble carbonates:

Ca + 2HCO3 = H2O + CO2 + CaCO3v

The solubility of calcium sulfate CaSO4 also decreases when heated, so it is part of the scale.

The hardness caused by the presence of calcium and magnesium bicarbonates in water is called carbonate or temporary, since it is eliminated by boiling. In addition to carbonate hardness, non-carbonate hardness is also distinguished, which depends on the content of sulfates and chlorides of calcium and magnesium in the water. These salts are not removed by boiling, and therefore non-carbonate hardness is also called constant hardness. Carbonate and non-carbonate hardness add up to total hardness.

To completely eliminate hardness, water is sometimes distilled. Boil water to remove carbonate hardness. The overall hardness is eliminated either by adding chemical substances, or with the help of so-called cation exchangers. When using the chemical method, soluble calcium and magnesium salts are converted into insoluble carbonates, for example, milk of lime and soda are added:

Ca + 2HCO3 + Ca + 2OH = 2H2O + 2CaCO3v

Ca + SO4 + 2Na + CO3 = 2Na + SO4 + CaCO3v

Removing stiffness with cation exchangers is a more advanced process. Cation exchangers are complex substances (natural compounds of silicon and aluminum, high molecular weight organic compounds), the composition of which can be expressed by the formula Na2R, where R is a complex acid residue. When water is filtered through a layer of cation exchanger, Na ions (cations) are exchanged for Ca and Mg ions:

Ca + Na2R = 2Na + CaR

Consequently, Ca ions from the solution pass into the cation exchanger, and Na ions pass from the cation exchanger into the solution. To restore the used cation exchanger, it is washed with a solution of common salt. In this case, the reverse process occurs: Ca ions in the cation exchanger are replaced by Na ions:

2Na + 2Cl + CaR = Na2R + Ca + 2Cl

The regenerated cation exchanger can be used again for water treatment.

In the form of a pure metal, Ca is used as a reducing agent for U, Th, Cr, V, Zr, Cs, Rb and some rare earth metals and their compounds. It is also used for the deoxidation of steels, bronzes and other alloys, for the removal of sulfur from petroleum products, for the dehydration of organic liquids, for the purification of argon from nitrogen impurities, and as a gas absorber in electric vacuum devices. Antifiction materials of the Pb - Na - Ca system, as well as Pb - Ca alloys, which are used to make the shell, have received great application in technology. electrical cables. Alloy Ca - Si - Ca (silicocalcium) is used as a deoxidizer and degasser in the production of quality steels.

Calcium is one of the biogenic elements necessary for the normal course of life processes. It is present in all tissues and fluids of animals and plants. Only rare organisms can develop in an environment devoid of Ca. In some organisms, the content of Ca reaches 38%: in humans - 1.4 - 2%. Cells of plant and animal organisms need strictly defined ratios of Ca, Na and K ions in extracellular media. Plants get Ca from the soil. According to their relation to Ca, plants are divided into calcephiles and calcephobes. Animals get Ca from food and water. Ca is necessary for the formation of a number of cellular structures, maintaining the normal permeability of outer cell membranes, for fertilizing the eggs of fish and other animals, and activating a number of enzymes. Ca ions transmit excitation to the muscle fiber, causing its contraction, increase the strength of heart contractions, increase the phagocytic function of leukocytes, activate the system of protective blood proteins, and participate in its coagulation. In cells, almost all Ca is in the form of compounds with proteins, nucleic acids, phospholipids, in complexes with inorganic phosphates and organic acids. In the blood plasma of humans and higher animals, only 20-40% Ca can be associated with proteins. In animals with a skeleton, up to 97 - 99% of all Ca is used as a building material: in invertebrates, mainly in the form of CaCO3 (mollusc shells, corals), in vertebrates, in the form of phosphates. Many invertebrates store Ca before molting to build a new skeleton or to provide vital functions in adverse conditions. The content of Ca in the blood of humans and higher animals is regulated by the hormones of the parathyroid and thyroid glands. Vitamin D plays the most important role in these processes. Ca absorption occurs in the anterior part of the small intestine. Assimilation of Ca worsens with a decrease in acidity in the intestine and depends on the ratio of Ca, phosphorus and fat in food. The optimal Ca/P ratios in cow's milk are about 1.3 (in potatoes 0.15, in beans 0.13, in meat 0.016). With an excess of P and oxalic acid in food, the absorption of Ca worsens. Bile acids accelerate its absorption. The optimal ratio of Ca/fat in human food is 0.04 - 0.08 g of Ca per 1 g. fat. Excretion of Ca occurs mainly through the intestines. Mammals during lactation lose a lot of Ca with milk. With violations of phosphorus-calcium metabolism in young animals and children, rickets develop, in adult animals - a change in the composition and structure of the skeleton (osteomalacia).

In medicine, Ca drugs eliminate disorders associated with a lack of Ca ions in the body (with tetany, spasmophilia, rickets). Ca preparations reduce hypersensitivity to allergens and are used to treat allergic diseases (serum sickness, sleeping fever, etc.). Ca preparations reduce increased vascular permeability and have an anti-inflammatory effect. They are used for hemorrhagic vasculitis, radiation sickness, inflammatory processes (pneumonia, pleurisy, etc.) and some skin diseases. It is prescribed as a hemostatic agent, to improve the activity of the heart muscle and enhance the action of digitalis preparations, as an antidote for poisoning with magnesium salts. Together with other drugs, Ca preparations are used to stimulate labor. Ca chloride is administered by mouth and intravenously. Ossocalcinol (15% sterile suspension of specially prepared bone powder in peach oil) has been proposed for tissue therapy.

Ca preparations also include gypsum (CaSO4), used in surgery for plaster casts, and chalk (CaCO3), administered orally with increased acidity of gastric juice and for the preparation of tooth powder.

Electronegativity 1.00 (Pauling scale) Electrode potential −2,76 Oxidation states 2 Ionization energy
(first electron) 589.4 (6.11) kJ/mol (eV) Thermodynamic properties of a simple substance Density (at n.a.) 1.55 g/cm³ Melting temperature 1112 K; 838.85°C Boiling temperature 1757 K; 1483.85°C Oud. heat of fusion 9.20 kJ/mol Oud. heat of evaporation 153.6 kJ/mol Molar heat capacity 25.9 J/(K mol) Molar volume 29.9 cm³/mol The crystal lattice of a simple substance Lattice structure cubic face centered Lattice parameters 5,580 Debye temperature 230 Other characteristics Thermal conductivity (300 K) (201) W/(m K) CAS number 7440-70-2 Emission spectrum

History and origin of the name

The name of the element comes from lat. calx (in the genitive case calcis) - "lime", "soft stone". It was proposed by the English chemist Humphry Davy, who in 1808 isolated calcium metal by the electrolytic method. Davy electrolyzed a mixture of wet hydrated lime on a platinum plate, which was the anode. A platinum wire immersed in liquid served as the cathode. As a result of electrolysis, calcium amalgam was obtained. Having driven away mercury from it, Davy received a metal called calcium.

isotopes

Calcium occurs in nature as a mixture of six isotopes: 40 Ca, 42 Ca, 43 Ca, 44 Ca, 46 Ca and 48 Ca, among which the most common - 40 Ca - is 96.97%. Calcium nuclei contain the magic number of protons: Z= 20 . isotopes 40
20 Ca20
And 48
20 Ca28
are two of the five doubly magic nuclei that exist in nature.

Of the six naturally occurring calcium isotopes, five are stable. The sixth isotope 48Ca, the heaviest of the six and very rare (its isotopic abundance is only 0.187%), undergoes double beta decay with a half-life of (4.39 ± 0.58)⋅10 19 years.

In rocks and minerals

Calcium, which migrates vigorously in the earth's crust and accumulates in various geochemical systems, forms 385 minerals (fourth in terms of the number of minerals).

Most of the calcium is contained in the composition of silicates and aluminosilicates of various rocks (granites, gneisses, etc.), especially in feldspar - anorthite Ca.

Calcium minerals such as calcite CaCO 3 , anhydrite CaSO 4 , alabaster CaSO 4 0.5H 2 O and gypsum CaSO 4 2H 2 O, fluorite CaF 2 , apatites Ca 5 (PO 4) 3 (F, Cl, OH), dolomite MgCO 3 CaCO 3 . The presence of calcium and magnesium salts in natural water determines its hardness.

Sedimentary rock, consisting mainly of cryptocrystalline calcite - limestone (one of its varieties is chalk). Under the action of regional metamorphism, limestone is transformed into marble.

Migration in the earth's crust

In the natural migration of calcium, a significant role is played by the “carbonate equilibrium”, associated with the reversible reaction of the interaction of calcium carbonate with water and carbon dioxide with the formation of soluble bicarbonate:

C a C O 3 + H 2 O + C O 2 ⇄ C a (H C O 3) 2 ⇄ C a 2 + + 2 H C O 3 − (\displaystyle (\mathsf (CaCO_(3)+H_(2)O+CO_(2 )\rightleftarrows Ca(HCO_(3))_(2)\rightleftarrows Ca^(2+)+2HCO_(3)^(-))))

(the equilibrium shifts to the left or right depending on the concentration of carbon dioxide).

Biogenic migration plays an important role.

In the biosphere

Calcium compounds are found in almost all animal and plant tissues (see below). A significant amount of calcium is part of living organisms. So, hydroxyapatite 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 are made of calcium carbonate CaCO 3, eggshell and others. In living tissues of humans and animals, 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 composition of the intercellular substance bone tissue).

Receipt

Free 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 4 C a O + 2 A l → C a A l 2 O 4 + 3 C a (\displaystyle (\mathsf (4CaO+2Al\rightarrow CaAl_(2)O_(4)+3Ca)))

Physical properties

The calcium metal exists in two allotropic modifications. Up to 443 °C resistant α-Ca with a cubic face-centered lattice (parameter A= 0.558 nm), higher stable β-Ca with a cubic body-centered lattice of the type α-Fe(parameter a= 0.448 nm). Standard enthalpy ∆ H 0 (\displaystyle \Delta H^(0)) transition α → β is 0.93 kJ/mol.

With a gradual increase in pressure, it begins to show the properties of a semiconductor, but does not become a semiconductor in the full sense of the word (it is no longer a metal either). With a further increase in pressure, it returns to the metallic state and begins to exhibit superconducting properties (the superconductivity temperature is six times higher than that of mercury, and far exceeds all other elements in conductivity). The unique behavior of calcium is similar in many ways to strontium (that is, the parallels in the periodic system are preserved).

Chemical properties

In the series of standard potentials, calcium is located to the left of hydrogen. The standard electrode potential of the pair Ca 2+ / Ca 0 −2.84 V, so that calcium actively reacts with water, but without ignition:

C a + 2 H 2 O → C a (O H) 2 + H 2 . (\displaystyle (\mathsf (Ca+2H_(2)O\rightarrow Ca(OH)_(2)+H_(2)\uparrow .)))

The presence of dissolved calcium bicarbonate in water largely determines the temporary 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.

Application

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 hard-to-reduce metals such as chromium, thorium and uranium. Calcium-lead alloys are used in some types of batteries and in the manufacture of bearings. Calcium granules are also used to remove traces of air from electrovacuum devices. Pure metallic calcium is widely used in metallothermy to obtain rare earth elements.

Calcium is widely used in metallurgy to deoxidize steel along with aluminum or in combination with it. Out-of-furnace processing with calcium-containing wires occupies a leading position due to the multifactorial effect of calcium on the physico-chemical state of the melt, the macro- and microstructure of the metal, the quality and properties of metal products and is an integral part of steel production technology. In modern metallurgy, an injection wire is used to introduce calcium into the melt, which is calcium (sometimes silicocalcium or aluminum calcium) in the form of a powder or pressed metal in a steel shell. Along with deoxidation (removal of oxygen dissolved in steel), the use of calcium makes it possible to obtain non-metallic inclusions that are favorable in nature, composition and shape, which do not collapse during further technological operations.

The 48 Ca isotope is one of the most effective and useful materials for the production of superheavy elements and the discovery of new elements in the periodic table. This is due to the fact that calcium-48 is a doubly magic nucleus, so its stability allows it to be sufficiently neutron-rich for a light nucleus; the synthesis of superheavy nuclei requires an excess of neutrons.

Biological role

The concentration of calcium in the blood, due to its importance for a large number of vital processes, is precisely regulated, and when proper nutrition and sufficient consumption of low-fat dairy products and vitamin D deficiency does not occur. Prolonged deficiency of calcium and/or vitamin D in the diet leads to an increased risk of osteoporosis and causes rickets in infancy.

Notes

1. Brinell hardness 200-300 MPa
2. Michael E. Wieser, Norman Holden, Tyler B. Coplen, John K. Böhlke, Michael Berglund, Willi A. Brand, Paul De Bièvre, Manfred Gröning, Robert D. Loss, Juris Meija, Takafumi Hirata, Thomas Prohaska, Ronny Schoenberg, Glenda O'Connor, Thomas Walczyk, Shige Yoneda, Xiang‑Kun Zhu. Atomic weights of the elements 2011 (IUPAC Technical Report) // Pure and Applied Chemistry. - 2013. - Vol. 85, no. 5 . - P. 1047-1078. - DOI:10.1351/PAC-REP-13-03-02 .
3. Editorial staff: Knunyants I. L. (editor-in-chief). Chemical encyclopedia: in 5 volumes - Moscow: Soviet Encyclopedia, 1990. - T. 2. - S. 293. - 671 p. - 100,000 copies.
4. Riley J.P. and Skirrow G. Chemical Oceanography V. 1, 1965.
5. Pritychenko B. Systematics of Evaluated Half-lives of Double-beta Decay // Nuclear Data Sheets. - 2014. - June (vol. 120). - S. 102-105. - ISSN 0090-3752. - DOI:10.1016/j.nds.2014.07.018 .[to correct]
6. Pritychenko B. List of Adopted Double Beta (ββ) Decay Values (indefinite) . National Nuclear Data Center, Brookhaven National Laboratory. Retrieved 6 December 2015.
7. Handbook of a chemist / Editorial board: Nikolsky B.P. and others - 2nd ed., corrected. - M.-L.: Chemistry, 1966. - T. 1. - 1072 p.
8. Newspaper. En: Elements under pressure
9. Calcium // Great Soviet Encyclopedia: [in 30 volumes] / ch. ed. A. M. Prokhorov. - 3rd ed. - M.: Soviet Encyclopedia, 1969-1978.
10. Dyudkin D. A., Kisilenko V. V. Influence of various factors on the assimilation of calcium from flux-cored wire with complex filler SK40 (rus.) // Elektrometallurgiya: zhurnal. - 2009. - May (No. 5). - S. 2-6.
11. Mikhailov G. G., Chernova L. A. Thermodynamic analysis of the processes of deoxidation of steel by calcium and aluminum (Russian) // Elektrometallurgiya: zhurnal. - 2008. - March (No. 3). - S. 6-8.
12. Shell Model of Nucleus
13. Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium; Ross AC, Taylor CL, Yaktine AL, Del Valle HB, editors (2011).

Compounds of calcium.

Cao- calcium oxide or quicklime, it is obtained by decomposition of limestone: CaCO 3 \u003d CaO + CO 2 is an oxide of an alkaline earth metal, so it actively interacts with water: CaO + H 2 O \u003d Ca (OH) 2

Ca(OH) 2 - calcium hydroxide or slaked lime, so the reaction CaO + H 2 O \u003d Ca (OH) 2 is called lime slaking. If the solution is filtered, lime water is obtained - this is an alkali solution, so it changes the color of phenolphthalein to crimson.

Hydrated lime is widely used in construction. Its mixture with sand and water is a good binding material. Under the action of carbon dioxide, the mixture hardens Ca (OH) 2 + CO 2 \u003d CaCO3 + H 2 O.

At the same time, part of the sand and the mixture turns into silicate Ca (OH) 2 + SiO 2 \u003d CaSiO 3 + H 2 O.

The equations Ca (OH) 2 + CO 2 \u003d CaCO 2 + H 2 O and CaCO 3 + H 2 O + CO 2 \u003d Ca (HCO 3) 2 play an important role in nature and in shaping the appearance of our planet. Carbon dioxide in the form of a sculptor and architect creates underground palaces in the strata of carbonate rocks. It is capable of moving hundreds and thousands of tons of limestone underground. Through cracks in rocks, water containing carbon dioxide dissolved in it enters the limestone thickness, forming cavities - castra caves. Calcium bicarbonate exists only in solution. Groundwater moves in the earth's crust, evaporating water under suitable conditions: Ca (HCO3) 2 \u003d CaCO3 + H 2 O + CO 2 , this is how stalactites and stalagmites are formed, the formation scheme of which was proposed by the famous geochemist A.E. Fersman. There are a lot of castra caves in the Crimea. Science studies them speleology.

Used in construction calcium carbonate CaCO3- this is chalk, limestone, marble. All of you have seen our railway station: it is finished with white marble brought from abroad.

experience: blow through a tube into a solution of lime water, it becomes cloudy .

Ca(OH) 2 + CO 2 = CaCO 3 + H 2 ABOUT

Adds acetic acid to the formed precipitate, effervescence is observed. carbon dioxide is released.

CaCO 3 +2CH 3 COOH \u003d Ca (CH 3 SOO) 2 +H 2 O + CO 2

THE TALE ABOUT THE CARBONATE BROTHERS.

Three brothers live on earth
From the Carbonate family.
The older brother is a handsome MARBLE,
Glorious in the name of Karara,
Excellent architect. He
He built Rome and the Parthenon.
Everyone knows LIMESTONE,
That's why it's named like that.
Famous for his work
Building a house behind the house.
Both able and able
The younger soft brother MEL.
How to draw, look
This CaCO 3!
Brothers love to frolic
Burn in a hot oven
CaO and CO 2 are then formed.
It's carbon dioxide
Each of you is familiar with him,
We breathe it out.
Well, this is Sao -
Hot burnt quicklime.
Add water to it
Thoroughly mixing
To avoid trouble
We protect our hands
Cool mixed LIME, but SLAKED!
milk of lime
The walls are whitewashed easily.
The bright house cheered up
Turning lime into chalk.
Hocus pocus for the people:
One has only to blow through the water,
How easy it is
Turned into milk!
Now it's pretty smart.
I get soda
Milk plus vinegar. Ay!
Foam is pouring over the edge!
All in worries, all in work
From dawn to dawn -
These brothers the Carbonates,
These CaCO 3!

Repetition: CaO– calcium oxide, quicklime;
Ca(OH) 2 - calcium hydroxide (slaked lime, lime water, milk of lime, depending on the concentration of the solution).
General - the same chemical formula Ca (OH) 2. Difference: lime water is a transparent saturated solution of Ca (OH) 2, and milk of lime is a white suspension of Ca (OH) 2 in water.
CaCl 2 - calcium chloride, calcium chloride;
CaCO 3 - calcium carbonate, chalk, shell rock marble, limestone.
L/R: collections. Next, we demonstrate the collection of minerals available in the school laboratory: limestone, chalk, marble, shell rock.
CaS0 4 ∙ 2H 2 0 - hydrated calcium sulfate, gypsum;
CaCO 3 - calcite, calcium carbonate is part of many minerals that cover 30 million km 2 on earth.

The most important of these minerals is limestone. Shell rocks, limestones of organic origin. It goes to the production of cement, calcium carbide, soda, all kinds of lime, in metallurgy. Limestone is the backbone of the construction industry and many building materials are made from it.

Chalk it's not just tooth powder and school chalk. It is also a valuable additive in the production of paper (coated - the highest quality) and rubber; in the construction and repair of buildings - as a whitewash.

Marble is a dense crystalline rock. There is color - white, but most often various impurities color it in different colors. Pure white marble is rare and is mainly used by sculptors (statues of Michelangelo, Rodin. In construction, colored marble is used as facing material(Moscow metro) or even as the main building material of palaces (Taj Mahal).

In the world of interesting "MAUSOLEUM" Taj Mahal ""

Shah Jahan from the Mughal dynasty held in fear and obedience almost all of Asia. In 1629, Mumzat Mahal, Shah Jahan's beloved wife, died at the age of 39 during childbirth on a campaign (it was their 14th child, all of them boys). She was unusually beautiful, bright, intelligent, the emperor obeyed her in everything. Before her death, she asked her husband to build a tomb, take care of the children, and not marry. The saddened king sent his envoys to all the big cities, the capitals of neighboring states - to Bukhara, Samarkand, Baghdad, Damascus, to find and invite the best craftsmen- in memory of his wife, the king decided to build the best building in the world. At the same time, messengers sent to Agra (India) plans for all the best buildings in Asia and the best building materials. They even brought malachite from Russia and the Urals. The chief masons came from Delhi and Kandahar; architects - from Istanbul, Samarkand; decorators - from Bukhara; gardeners from Bengal; the artists are from Damascus and Baghdad, and the well-known master Ustad-Isa was in charge.

Together, over 25 years, a chalk marble structure was built, surrounded by green gardens, blue fountains and red sandstone mosques. 20,000 slaves erected this miracle of 75 m (with a 25-storey building). Nearby, he wanted to build a second mausoleum of black marble for himself, but did not have time. He was overthrown from the throne by his own son (2nd, and he also killed all his brothers).

The ruler and ruler of Agra spent the last years of his life looking out of the narrow window of his dungeon. 7 years so the father admired his creation. When his father went blind, his son made him a system of mirrors so that his father could admire the mausoleum. He was buried in the Taj Mahal, next to his Mumtaz.

Those entering the mausoleum see cenotaphs - false tombs. The places of eternal rest of the great khan and his wife are located below, in the basement. Everything there is encrusted with precious stones that glow as if alive, and the branches of fabulous trees, intertwined with flowers, adorn the walls of the tomb with intricate patterns. Turquoise-blue lapis lazuli, green-black nephrites and red amethysts processed by the best carvers sing the love of Shah Jahal and Mumzat Mahal.

Every day tourists rush to Agra who want to see the true wonder of the world - the mausoleum of the Taj Mahal, as if hovering above the ground.

CaCO 3 - This construction material the external skeleton of molluscs, corals, shells, etc., egg shells. (illustrations or Animals of the coral biocenosis” and display of a collection of sea corals, sponges, shell rock).