The calcium It is an alkaline earth metal that belongs to group 2 of the periodic table (Mr. Becambara). This metal occupies the fifth place in abundance among the elements present in the earth's crust; behind iron and aluminum. It is represented by the chemical symbol Ca, and its atomic number is 20.
Calcium represents 3.64% of the earth's crust and is the most abundant metal in the human body, representing 2% of its weight. He is not free in nature; but it is part of numerous minerals and chemical compounds.
For example, it is found in the mineral calcite, which in turn is part of limestone. Calcium carbonate is present in the earth as marble, dolomite, eggshell, coral, pearls, stalactites, stalagmites, as well as in the shells of many marine animals or snails.
In addition, calcium is part of other minerals, such as gypsum, anhydrite, fluorite, and apatite. It is not surprising then that it is synonymous with bones on a cultural level.
When calcium is exposed to air, it becomes covered with a yellowish coating, the product of a mixture of calcium oxide, nitride and hydroxide. However, freshly cut, the surface is lustrous, silvery-whitish. It is soft with a hardness on the Mohs scale of 1.75.
Calcium performs numerous functions in living beings, among them it is part of compounds that determine the structure and functioning of the bone system; intervenes in the coagulation cascade by activating several coagulation factors, identified as Factor IV.
In addition, calcium intervenes in muscle contraction, allowing the union of contractile proteins (actin and myosin); and facilitates the release of some neurotransmitters, including acetylcholine.
Chemically it almost always participates in its organic or inorganic compounds such as the divalent cation Catwo+. It is one of the cations with the highest coordination number, that is, it can interact with several molecules or ions at the same time.
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Calcium compounds such as lime (CaO) or gypsum (CaSO4) have been used for millennia by man, unaware of their chemical structure. Lime as a building material and plaster for making the sculptures were used 7,000 years BC..
In Mesopotamia a lime kiln was found that was used 2,500 BC. In a close period of time, plaster was used during the construction of the Great Pyramid of Giza.
Joseph Black (1755) explained that lime is lighter than the limestone (calcium carbonate) that gives rise to it. This is because it loses carbon dioxide during heating..
Antoine Lavoiser (1787) concluded that lime must be an oxide of an unknown chemical element.
Sir Humphrey Davy (1808) precisely in the year that he discovered boron, he did the same with calcium using the electrolysis technique, used by Jakar Berzelius and Magnus Martin..
Davy isolated calcium and magnesium using the same experimental design. He mixed the calcium oxide with the mercury (II) oxide on a platinum plate, used as an anode (+), while the cathode (-) was a platinum wire partially submerged in mercury.
Electrolysis produced an amalgam of calcium and mercury. To purify the calcium, the amalgam was subjected to distillation. However, pure calcium was not obtained..
Silvery-whitish metal, changes to greyish white when exposed to air. In humid air it takes on a cloudy bluish gray. Solid or dry powder. Face-centered crystalline structure.
40.078 g / mol.
842 ºC.
1,484 ºC.
-1.55 g / cm3 at room temperature.
-1.378 g / cm3 in liquid state at melting point.
8.54 kJ / mol.
154.7 kJ / mol.
25.929 J / (mol K).
0.63 J / gK
1.0 on the Pauling scale
-First ionization 589.8 kJ / mol
-Second ionization 1,145 kJ / mol
-Third ionization 4,912 kJ / mol
-Fourth ionization 6,490.57 kJ / mol and there are 4 more ionization energies.
197 pm
176 ± 10 pm
22.3 µm / m K at 20 ºC.
201 W / m K
336 nΩ · m at 20 ºC.
1.75 on the Mohs scale.
Calcium has 6 natural isotopes: 40AC, 42AC, 43AC, 44AC, 46Ca and 48Ca, and 19 radioactive synthetic isotopes. The most abundant isotopes are 40Ca (96.94%), the 44Ca (2,086%) and the 42Ca (0.647%).
Calcium reacts spontaneously with water, producing calcium hydroxide and hydrogen gas. It reacts with oxygen and nitrogen in the air, producing respectively calcium oxide and calcium nitride. When splitting, it spontaneously burns in air.
When calcium is heated, it reacts with hydrogen to form a halide. It also reacts with all halogens to form halides. It also reacts with boron, sulfur, carbon and phosphorus..
Calcium atoms are joined by metallic bonds, contributing their two valence electrons to the tide of electrons. Thus, the interaction between the Ca atoms and the resulting electronic bands ends up defining a crystal with a face-centered cubic structure (ccc, in Spanish; or fcc, in English, for face-centered cubic).
If this calcium crystal is heated to a temperature around 450 ° C, it undergoes a transition to the hcp phase (compact hexagonal, or hexagonal closest packed). That is, the structure becomes more dense, as if the movement of electrons and the vibrations of atoms contracted the distance that separates them.
The calcium atom has the following electronic configuration:
[Ar] 4stwo
Which would explain that the two valence electrons for this metal come from its outermost 4s orbital. When it loses them, the divalent cation Ca is formedtwo+, isoelectronic to noble gas argon; that is, both Ar and Catwo+ have the same number of electrons.
It is the 4s orbitals of calcium that combine to establish the valence band of these crystals. The same happens with the empty 4p orbitals, which establish a conduction band.
Calcium is produced commercially by the electrolysis of molten calcium chloride. The following reactions occur at the electrodes:
At the anode: 2Cl- (l) => Cltwo (g) + 2e-
Calcium is deposited as a metal on the cathode by capturing electrons ionic calcium.
At the cathode: Catwo+ (l) + 2 e- => Ca (s)
On a small scale, calcium can be produced by reducing calcium oxide with aluminum, or calcium chloride with metallic sodium..
6 CaO + 2 Al => 3 Ca + Ca3To thetwoOR6
CaCltwo + 2 Na => Ca + NaCl
Calcium is used as an additive in the manufacture of glass bulbs, being added to the bulb during its initial manufacturing stage. It is also added at the end to combine with the gases left inside the bulb..
It is used as a disintegrator in the production of metals such as copper and steel. The alloy of calcium and cesium is used in the flints of the lighters to generate the sparks. Calcium is a reducing agent, but it also has deoxidation and deoxidation applications.
Calcium is used in the preparation of metals such as chromium, thorium, uranium, zirconium and others from their oxides. It is used as an alloying agent for aluminum, copper, lead, magnesium, and other base metals; and as a deoxidizer for some high temperature alloys.
Calcium in alloy with lead (0.04%) serves as a sheath for telephone cables. It is used in alloy with magnesium in orthopedic implants to prolong their life.
It is a filler material in ceramics, glass, plastics and paints, as well as a raw material for the production of lime. High purity synthetic carbonate is used medicinally as an antacid and dietary calcium supplement. It is also used as an additive in food.
Calcium oxide is used in the construction industry, being used in veneering the walls. It is also incorporated into concrete. In the 19th century, blocks of calcium oxide were burned to illuminate the stages with intense white light..
Lime (again, calcium oxide) is used to remove unwanted components such as silicon dioxide (SiOtwo) present in iron material. The product of the reaction is calcium silicate (CaSiO3) called "scum".
Lime combines with water to form calcium hydroxide; This compound flocculates and sinks, dragging impurities to the bottom of the tanks..
The interior of the chimneys is lined with lime to eliminate fumes from the factories. For example, it captures sulfur dioxide (SOtwo), which contributes to acid rain, and transforms it into calcium sulfite (CaSO3).
Calcium chloride is used to control road ice; conditioner for the tomato present in preserves; manufacture of car and truck bodies.
It is commonly presented as CaSO42HtwoO (plaster), being used as a soil conditioner. Calcined gypsum is used in the manufacture of tiles, boards, and laths. It is also used for immobilization of bone fractures.
Calcium phosphates are found in various forms in nature and are used as fertilizers. The acid salt of calcium (CaHtwoPO4) is used as a fertilizer and stabilizer for plastics. Calcium phosphate is found as part of bone tissue, especially as hydroxyapatite.
There are numerous calcium compounds with various applications. For example, calcium carbide is used to obtain acetylene, used in welding torches. Calcium alginate is used as a thickening agent in food products such as ice cream.
Calcium hypochlorite is used as a bleaching agent, deodorant, fungicide and algaecide.
Calcium permanganate is a rocket propellant. It is also used as a water purifying agent, and in textile production.
Calcium fulfills numerous functions in living beings:
-Intervenes in the coagulation cascade like Factor IV.
-It is necessary for the activation of several coagulation factors, including thrombin.
-In skeletal muscle, calcium releases the inhibitory action of a protein system on muscle contraction, allowing actin-myosin bridges to form, leading to contraction..
-Stabilizes the ion channels of excitable cells. In hypocalcemia, sodium channels are activated, which causes sodium to enter the cells, and a sustained contraction (tetany) can be generated that can be lethal.
-In addition, calcium promotes the release of the neurotransmitter acetylcholine at presynaptic terminals..
Reacts exothermically with water. Therefore, it can cause serious injury to the mouth, esophagus or stomach once swallowed..
Workers are exposed to this risk in places where the element calcium is produced or those where metal is applied. The precautions are to protect yourself with masks that avoid breathing dust, adequate clothing and ventilation..
Hypercalcemia is extremely dangerous and can be caused mainly by excessive secretion of parathyroid hormone or an exaggerated intake of vitamin D. An excessive intake of calcium, for example greater than 2.5 g / day, is rarely a cause of hypercalcemia.
Excess calcium accumulates in the kidneys causing kidney stones and kidney nephrosis. In addition, the accumulation of calcium in the walls of the blood vessels modifies their elasticity, which could be the cause of hypertension, slowed blood flow and thrombosis..
A basic precaution is the inclusion of calcaemia among the laboratory tests, when the doctor observes characteristics that make the patient suspect hypercalcemia and initiate appropriate treatment..
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