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 serial number 20. Also, the chemical periodic table shows the atomic weight of calcium - 40.08, which is the average value of the existing isotopes of this atom.

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

Characterization of calcium as a simple substance

Under normal conditions, this element is a metal, silvery-white in color. 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 the solid state of aggregation, it is not part of the human body, therefore it is important for industrial and technical needs (mainly chemical syntheses).

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

Crystal cell

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

• cubic face-centric;
• volume-centric.

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

Being in nature

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

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 sources of 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 current. To date, still the most relevant way to obtain this metal is the electrolysis of its salts, such as:

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

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

Physical Properties

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

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 the bones, tooth enamel in an amount of about 2.5% of the total body weight. This is quite a lot and plays an important role in strengthening these structures, maintaining their strength and stability. The growth of the body without it is impossible.
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, however, external means of strengthening them are also formations of this metal. Among them:

• shellfish;
• mussels and oysters;
• sponges;
• coral polyps.

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

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

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

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

• dairy and sour-milk products;
• a 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 is a chemical element of group II with atomic number 20 in the periodic system, denoted by the symbol Ca (lat. Calcium). Calcium is a soft, silvery-gray alkaline earth metal.

20 element of the periodic table 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 isolated metallic calcium in 1808.
Calcium compounds - limestone, marble, gypsum (as well as lime - a product of burning limestone) have been used in construction for several millennia ago.
Calcium is one of the most abundant elements on Earth. Calcium compounds are found in almost all animal and plant tissues. It accounts for 3.38% of the mass of the earth's crust (5th place in abundance after oxygen, silicon, aluminum and iron).

Finding calcium in nature

Due to the high chemical activity of calcium in the free form in nature is not found.
Calcium accounts for 3.38% of the mass of the earth's crust (5th place in abundance after oxygen, silicon, aluminum and iron). The content of the element in sea water is 400 mg/l.

isotopes

Calcium occurs in nature in the form of a mixture of six isotopes: 40Ca, 42Ca, 43Ca, 44Ca, 46Ca and 48Ca, among which the most common - 40Ca - 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 number nuclei found in nature.
Of the six naturally occurring calcium isotopes, five are stable. The sixth 48Ca isotope, the heaviest of the six and very rare (its isotopic abundance is only 0.187%), undergoes double beta decay with a half-life of 1.6 1017 years.

In rocks and minerals

Most calcium is contained in the composition of silicates and aluminosilicates of various rocks (granites, gneisses, etc.), especially in feldspar - anorthite Ca.
In the form of sedimentary rocks, calcium compounds are represented by chalk and limestone, 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 0.5H2O and gypsum CaSO4 2H2O, fluorite CaF2, apatites 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, 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).

The biological role of calcium

Calcium is a common macronutrient in plants, animals and humans. In humans and other vertebrates, most of it is in the skeleton and teeth. Calcium is found in bones in the form of hydroxyapatite. The "skeletons" of most groups of invertebrates (sponges, coral polyps, mollusks, etc.) consist of various forms of calcium carbonate (lime). Calcium ions are involved in blood coagulation processes, and also serve as one of the universal second messengers inside cells and regulate a variety of intracellular processes - muscle contraction, exocytosis, including the secretion of hormones and neurotransmitters. The concentration of calcium in the cytoplasm of human cells is about 10−4 mmol/l, in intercellular fluids about 2.5 mmol/l.

The need for calcium depends on age. For adults aged 19-50 years and children aged 4-8 inclusive, the daily requirement (RDA) is 1000 mg (contained in approximately 790 ml of milk with a fat content of 1%), and for children aged 9 to 18 years inclusive - 1300 mg per day (contained in approximately 1030 ml of milk with a fat content of 1%). In adolescence, adequate calcium intake is very important due to the intensive growth of the skeleton. However, according to research in the US, only 11% of girls and 31% of boys aged 12-19 achieve their needs. In a balanced diet, most of the calcium (about 80%) enters the child's body with dairy products. The remaining calcium comes from cereals (including whole grain bread and buckwheat), legumes, oranges, greens, nuts. Dairy products based on milk fat (butter, cream, sour cream, cream-based ice cream) contain practically no calcium. The more milk fat in a dairy product, the less calcium it contains. Calcium absorption in the intestine occurs in two ways: transcellular (transcellular) and intercellular (paracellular). The first mechanism is mediated by the action of the active form of vitamin D (calcitriol) and its intestinal receptors. It plays a big role in low to moderate calcium intake. With a higher calcium content in the diet, intercellular absorption begins to play the main role, which is associated with a large calcium concentration gradient. Due to the transcellular mechanism, calcium is absorbed to a greater extent in the duodenum (due to the highest concentration of receptors in calcitriol there). Due to intercellular passive transfer, calcium absorption is most active in all three sections of the small intestine. Calcium absorption is paracellularly promoted by lactose (milk sugar).

Calcium absorption is hindered by some animal fats (including cow's milk fat and beef fat, but not lard) and palm oil. The palmitic and stearic fatty acids contained in such fats are cleaved off during digestion in the intestines and, in the free form, firmly bind calcium, forming calcium palmitate and calcium stearate (insoluble soaps). In the form of this soap with a chair, both calcium and fat are lost. This mechanism is responsible for decreased calcium absorption, reduced bone mineralization, and reduced indirect measures of bone strength in infants with palm oil (palm olein) based infant formula. In these children, the formation of calcium soaps in the intestines is associated with hardening of the stool, a decrease in its frequency, as well as more frequent regurgitation and colic.

The concentration of calcium in the blood, due to its importance for a large number of vital processes, is precisely regulated, and with proper nutrition and sufficient intake 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.

Excessive doses of calcium and vitamin D can cause hypercalcemia. The maximum safe dose for adults aged 19 to 50 inclusive is 2500 mg per day (about 340 g of Edam cheese).

Thermal conductivity

DEFINITION

Calcium- the twentieth element of the Periodic table. Designation - Ca from the Latin "calcium". Located in the fourth period, IIA group. Refers to metals. The core charge is 20.

Calcium is one of the most abundant elements in nature. It contains approximately 3% (mass) in the earth's crust. It occurs as numerous deposits of limestone and chalk, as well as marble, which are natural varieties of calcium carbonate CaCO 3 . Gypsum CaSO 4 × 2H 2 O, phosphorite Ca 3 (PO 4) 2 and, finally, various calcium-containing silicates are also found in large quantities.

In the form of a simple substance, calcium is a malleable, rather hard white metal (Fig. 1). In air, it quickly becomes covered with a layer of oxide, and when heated, it burns with a bright reddish flame. Calcium reacts relatively slowly with cold water, but quickly displaces hydrogen from hot water, forming hydroxide.

Rice. 1. Calcium. Appearance.

Atomic and molecular weight of calcium

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

Since in the free state calcium exists in the form of monatomic Ca molecules, the values ​​of its atomic and molecular masses are the same. They are equal to 40.078.

Isotopes of calcium

It is known that in nature calcium can be found in the form of four stable isotopes 40Ca, 42Ca, 43Ca, 44Ca, 46Ca and 48Ca, with a clear predominance of the 40Ca isotope (99.97%). Their mass numbers are 40, 42, 43, 44, 46 and 48, respectively. The nucleus of the atom of the calcium isotope 40 Ca contains twenty protons and twenty neutrons, and the remaining isotopes differ from it only in the number of neutrons.

There are artificial calcium isotopes with mass numbers from 34 to 57, among which the most stable is 41 Ca with a half-life of 102 thousand years.

Calcium ions

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

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 .

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

Ca 0 -2e → Ca 2+.

Molecule and atom of calcium

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

calcium alloys

Calcium serves as an alloying component of some lead alloys.

Examples of problem solving

EXAMPLE 1

The task

Write the reaction equations that can be used to carry out the following transformations: Ca → Ca(OH) 2 → CaCO 3 → Ca(HCO 3) 2.

Answer

By dissolving calcium in water, you can get a cloudy solution of a compound known as "milk of lime" - calcium hydroxide: Ca + 2H 2 O → Ca (OH) 2 + H 2. By passing carbon dioxide through a solution of calcium hydroxide, we get calcium carbonate: 2Ca(OH) 2 + CO 2 → CaCO 3 + H 2 O. By adding water to calcium carbonate and continuing to pass carbon dioxide through this mixture, we obtain calcium bicarbonate: CaCO 3 + H 2 O + CO 2 → Ca(HCO 3) 2.

Learning to understand our analyzes Elena V. Pogosyan

Calcium (Ca2+)

Calcium (Ca2+)

Calcium (Ca2+) - the main component of bone tissue and teeth, is involved in blood clotting, muscle contraction, and the activity of some endocrine glands. Calcium absorption and excretion is controlled by hormones and active vitamin D metabolites.

About 50% of plasma calcium is in ionized form, 45% is associated with albumin and about 5% with complexing ions (phosphate, citrate). Ionized calcium has the highest physiological activity.

Normally, the concentration of total calcium in the serum (plasma) of the blood is 2.00-2.80 mmol / l, ionized - 1.10-1.40 mmol / l.

An increase in the concentration of calcium in the blood (hypercalcemia) is observed when:

# excess in the administration of vitamin d in the child's body;

# disintegration of tissue cells during softening of bones caused by malignant tumors;

# primary hyperparathyroidism;

# hyperthyroidism;

# using hormone replacement therapy (HRT); an overdose of vitamins;

# chronic enteritis.

Hypocalcemia occurs when:

# kidney disease;

# Decreased secretion of parathyroid hormone into the blood;

# decrease in the content of albumin in plasma;

# vitamin D deficiency;

# rickets and spasmophilia;

# malabsorption of calcium in the intestine;

# chronic kidney failure;

# cirrhosis of the liver;

# adrenal hyperplasia;

# under the influence of antiepileptic therapy.

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In ancient times, people used calcium compounds for construction. Basically, it was calcium carbonate, which was in the rocks, or the product of its burning - lime. Marble and plaster were also used. Previously, scientists believed that lime, which is calcium oxide, is a simple substance. This misconception existed until the end of the 18th century, until Antoine Lavoisier expressed his assumptions about this substance.

Lime mining

At the beginning of the 19th century, the English scientist Humphrey Davy discovered pure calcium using electrolysis. Moreover, he received calcium amalgam from slaked lime and mercury oxide. Then, after distilling the mercury, he obtained metallic calcium.

The reaction of calcium with water is violent, but is not accompanied by ignition. Due to the abundant release of hydrogen, the plate with calcium will move through the water. A substance is also formed - calcium hydroxide. If phenolphthalein is added to the liquid, it will turn bright crimson - therefore, Ca(OH)₂ is a base.

Ca + 2H₂O → Ca(OH)₂↓ + H₂

The reaction of calcium with oxygen

The reaction of Ca and O₂ is very interesting, but the experiment cannot be performed at home, as it is very dangerous.

Consider the reaction of calcium with oxygen, namely, the combustion of this substance in air.

Attention! Do not try to repeat this experience yourself! you will find safe chemistry experiments you can do at home.

Let us take potassium nitrate KNO₃ as a source of oxygen. If calcium was stored in a kerosene liquid, then before the experiment it must be cleaned with a burner, holding it over a flame. Next, calcium is dipped into KNO₃ powder. Then calcium with potassium nitrate must be placed in the flame of the burner. Potassium nitrate decomposes into potassium nitrite and oxygen. The released oxygen ignites the calcium, and the flame turns red.

KNO₃ → KNO₂ + O₂

2Ca + O₂ → 2CaO

It is worth noting that calcium reacts with some elements only when heated, these include: sulfur, boron, nitrogen and others.