Calcium


from Wikipedia, the free encyclopedia
properties
General
Name , symbol , atomic number Calcium, Ca, 20
Element category Alkaline earth metals
Group , period , block 2 , 4 , p
Appearance silvery white
CAS number 7440-70-2
EC number 231-179-5
ECHA InfoCard 100.028.344
ATC code

A12 AA

Mass fraction of the earth's envelope 3.39%
Atomic
Atomic mass 40.078 (4) and
Atomic radius (calculated) 180 (194) pm
Covalent radius 176 pm
Van der Waals radius 231 pm
Electron configuration [ Ar ] 4s 2
1. Ionization energy 6th.113 155 4 (3) eV 589.83 kJ / mol
2. Ionization energy 11.871 719 (4) eV 1 145.45 kJ / mol
3. Ionization energy 50.91316 (25) eV4 912.37 kJ / mol
4. Ionization energy 67.2732 (21) eV6 490.9 kJ / mol
5. Ionization energy 84.34 (8) eV8 140 kJ / mol
Physically
Physical state firmly
Crystal structure Cubic area-centered
density 1.55 g / cm 3 (20 ° C )
Mohs hardness 1.75
magnetism paramagnetic ( Χ m = 1.9 10 −5 )
Melting point 1115 K (842 ° C)
boiling point 1760 K (1487 ° C)
Molar volume 26.20 · 10 −6 m 3 · mol −1
Heat of evaporation 153 kJ / mol
Heat of fusion 8.54 kJ mol −1
Speed ​​of sound 3810 m s −1 at 293.15 K.
Specific heat capacity 647.3 J kg −1 K −1
Work function 2.87 eV
Electric conductivity 29.4 · 10 6 A · V −1 · m −1
Thermal conductivity 200 W m −1 K −1
Chemically
Oxidation states (+1) +2
Normal potential −2.84 V (Ca 2+ + 2 e - → Ca)
Electronegativity 1.00 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP
40 approx 96.941  % Stable
41 Approx {syn.} 103,000 a ε 0.421 41 K
42 approx 0.647% Stable
43 Approx 0.135% Stable
44 Approx 2.086% Stable
45 approx {syn.} 162.61 d β− 0.257 45 Sc
46 Approx 0.004% Stable
47 Approx {syn.} 4.536 d β− 1.992 47 Sc
48 approx 0.187% > 6 · 10 18 a β − β− 4,272 48 Ti
For other isotopes see list of isotopes
NMR properties
  Spin
quantum
number I
γ in
rad · T −1 · s −1
E r  ( 1 H) f L at
B = 4.7 T
in MHz
43 Approx 7/2 0−1.803 10 7 6.4 · 10 −3 013.49
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
02 - Highly / extremely flammable

danger

H and P phrases H: 261
EUH: 014
P: 223-232-501-402 + 404
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions .

Calcium ( eingedeutscht calcium written) is a chemical element with the element symbol Ca and atomic number 20. In the periodic table , it is on the second main group , or of the 2nd  IUPAC-group and therefore is one of the alkaline earth metals . The notation calcium corresponds to the IUPAC standard and is considered technical language.

Elemental calcium is a shiny, silvery white metal . In relation to the mass fraction ( ppmw ), it is the fifth most abundant element in the earth's shell after oxygen , silicon , aluminum and iron . Due to its strong reactivity , it is only chemically bound as a component of minerals . These include B. calcite , aragonite and dolomite in limestone , marble and chalk as well as gypsum ( calcium sulfate ). Hydroxyapatite ( calcium phosphate ) is an essential component of bones and teeth .

history

Humphry Davy presented elemental calcium for the first time

The name "calcium" is derived from the Latin word calx . This is how the Romans called lime, limestone, chalk and mortar made from lime ( building lime ).

Elemental calcium was first obtained by Humphry Davy in 1808 by evaporating the mercury from electrolytically obtained calcium amalgam .

Occurrence

Almost colorless calcite - Crystal

Calcium only occurs in bound form in the environment, for example in limestone , marble , chalk , gypsum and the minerals calcite , aragonite , dolomite , anhydrite , fluorite and apatite . An exception is probably a variety of fluorite (" stinkspar "), in whose crystal lattice colloidal calcium was probably formed by natural ionizing radiation . Calcium-containing minerals such as calcite and gypsum are available in large quantities (e.g. in the Alps, mountain-accompanying trains consist of limestone - Northern Limestone Alps and Southern Limestone Alps ).

Calcium compounds are soluble in water , whereby the solubility of calcium in the groundwater is largely determined by the excess carbon dioxide ( calcium saturation ). Therefore, the question of which calcium compound is stable in the groundwater essentially depends on the pH of the groundwater. Calcite (Ca [CO 3 ]) and gypsum (Ca [SO 4 ] · 2H 2 O) predominate as calcium compounds at medium to alkaline pH values . At a low pH, calcium appears as Ca 2+ .

The main process in which calcium enters the groundwater is the weathering of rocks containing calcium such as limestone .

As an essential component of living matter, calcium is involved in the structure of leaves , bones , teeth and shells . In addition to K + and Na + , Ca 2+ plays an important role in the transmission of stimuli in nerve and muscle cells . Calcium ions also play an important role in signal transduction in other cells .

properties

Crystals of calcium stored in a protective atmosphere
Partly oxidized calcium

Calcium is a light, very ductile , silvery metal whose properties are very similar to the heavier alkaline earth metals magnesium , strontium , barium and radium . It crystallizes in the face-centered cubic arrangement like strontium. Above 450 ° C it transforms into a hexagonal crystal structure like magnesium.

It is a good conductor of electricity and heat . When heated, it first changes to a liquid and then a gaseous state and loses its metallic properties. When it is pressurized , it begins to lose its metallic properties and electrical conductivity . However, if the pressure is increased further, the metallic properties are restored and it shows the properties of a superconductor , which by many times exceeds other elements in these parameters.

Calcium is softer than lead but cannot be cut with a knife. It starts up quickly in the air . It reacts violently with water to form calcium hydroxide and hydrogen .

Reaction of calcium with water

In the air it burns to form calcium oxide and - to a small extent - calcium nitride . Finely divided calcium is self-igniting ( pyrophoric ).

When heated, it reacts with nitrogen , hydrogen , carbon , silicon , boron , phosphorus , sulfur and other substances . Outside, it reacts instantly with oxygen and carbon dioxide , giving it a gray coating.

It reacts violently with acids and sometimes goes up in flames . Due to its high reactivity , elemental calcium is stored in the laboratory in a dark glass with a tightly closed lid and under a layer of paraffin or kerosene .

Calcium belongs to the alkaline earth metals . In chemical compounds it is almost only present in the oxidation number +2.

Manufacturing

The metal is produced in a vacuum by reducing quick lime (calcium oxide) with aluminum powder at 1200 ° C. Although aluminum has a lower reactivity and enthalpy than calcium, so the equilibrium of the reaction

is actually almost completely on the left-hand side of this equation, but this manufacturing process still works because the calcium that is formed constantly evaporates at this temperature and thus disappears from its equilibrium. Purification takes place by distilling the calcium.

use

Metallic calcium is used as reducing agent in the metallurgy for the production of metals such as thorium , vanadium , zirconium , yttrium and other metals of the rare earths , as a reducing agent in the steel and aluminum production, as an alloying element in aluminum, beryllium - copper - lead - and magnesium alloys and as a starting material for the production of calcium hydride .

The technical use of calcium takes place predominantly in bound form.

Limestone (mainly calcium carbonate, CaCO 3 ) and dolomite (CaMg (CO 3 ) 2 ) are two of the most important raw materials in today's industry:

  • Slagging agent in steel production . The consumption is 0.5 tons of limestone per ton of steel
  • Starting material for the production of quick lime
  • Chalk as a filler for plastics , for example PVC . The aim is to improve stiffness and impact strength, as well as to reduce shrinkage. The also greatly increased thermal conductivity allows higher work cycles during extrusion .
  • Fine-grain calcium carbonate is used as a filler in high-quality, wood-free paper
  • Finely ground lime or dolomite is used as fertilizer lime in agriculture and forestry or as fodder lime in animal husbandry.

Because of its functions in organisms , calcium is also used as a drug.

proof

The flame color of calcium

In addition to the orange-red color of the flame with calcium, calcium, strontium and barium cations can be detected with sulfuric acid or ammonium sulfate solution . This detection reaction produces white, acid-insoluble precipitates . Even with carbonate - oxalate - and dichromate - anions can rainfall different low solubility are produced. Their detailed investigation then can one distinguish between the alkaline earth metal - cations (cf. below. Cation separation gear and Ammoniumcarbonatgruppe ).

In routine analysis ( clinical chemistry , environmental chemistry , water chemistry ) calcium is determined quantitatively down to the trace range using flame photometry . The limit of quantification is 100 µg / l. In higher concentrations also is titration with EDTA against Eriochrome black T possible. For the gravimetric determination of calcium, it is precipitated with oxalate and annealed at 600 ° C to obtain the calcium carbonate weighing form .

Preanalytics

The calcium concentration is determined in routine laboratory diagnostics in the blood and urine . Calcium is an important parameter in the diagnosis of bone and calcium metabolism . Both serum and heparinized plasma can be used as blood samples ; accordingly, the calcium concentration in the blood is referred to as serum calcium or plasma calcium for short . In the case of plasma , it should be noted that no calcium-binding anticoagulants (such as citrate or EDTA ) are used. Blocking the vein for too long before taking a blood sample can lead to incorrectly elevated values.

Analytics

50% of calcium is present in the blood as Ca 2+ ions, 35% bound to proteins ( albumin , globulins ) and 15% bound to complexes ( bicarbonate , lactate , citrate , phosphate ). The serum value of calcium moves within narrow limits with a normal total calcium of 2.2 to 2.6 mmol / L (9 to 10.5 mg / dL) and a normal ionized calcium of 1.1 to 1.4 mmol / L (4.5 to 5.6 mg / dL). The biological effects of calcium are determined by the availability of free calcium ions, so the decisive factor is the ionized calcium.

The total calcium concentration (total calcium) in the blood is of albumin - concentration -dependent and must be corrected accordingly. Alternatively, the concentration of the ionized calcium is measured directly . The total calcium in the serum is determined by means of absorption spectrometry or flame atomic emission spectrometry . The physical properties of calcium are used here.

Ionized calcium is determined with ion-selective electrodes .

interpretation

The calcium concentration in the body is extremely tightly controlled. An increased calcium concentration is called hypercalcemia , a decreased calcium concentration is called hypocalcemia . Specific causes and symptoms can be found there.

Measured value Reference range
Total calcium 8.4-10.5 mg / dL 2.2-2.6 mmol / l
Ionized calcium 4.6-5.4 mg / dl 1.15-1.35 mmol / L

The exact values ​​depend on the measuring method , which is why the reference value given by the laboratory is decisive. In children, the values ​​are slightly higher than in adults.

Functions in the organism

Calcium is a quantity element (definition: element with more than 50 mg per kg of body weight) and is therefore not a trace element . With a body weight of 1 to 1.1 kg, calcium is the most abundant mineral in the human organism. 99% of the calcium found in the body is bound in bones (over 90%) and teeth - the calcium-rich compound hydroxylapatite (Ca 5 (PO 4 ) 3 (OH)) gives them stability and strength. At the same time, the bones serve as a reservoir for calcium - if there is a calcium deficiency, part of it can be released from the bones and made available for other tasks. Bone decalcification, osteoporosis , occurs mainly in older people. Increased calcium intake of around 1 g / day helps prevent osteoporosis (basic therapy DVO ).

Within the cells, calcium plays a decisive role in stimulating muscles and nerves , glycogen metabolism, cell division and activating certain enzymes and hormones. As Setsuro Ebashi demonstrated for the first time , it is only the influx of calcium ions into the muscle cells that causes the muscles to contract. Outside the cells, calcium is involved in blood clotting and the maintenance of cell membranes . There must be a constant concentration of 2.1 to 2.6 mmol / l calcium in the blood serum, with about 1 to 1.5 mmol / l in ionized form. It is regulated by the hormones calcitriol , calcitonin and parathyroid hormone . Only 0.1% of the calcium present in the body is found in the extracellular space , of which 30 to 55% are bound to proteins , 5 to 15% are in the form of complexes (e.g. calcium hydrogen carbonate , calcium citrate , calcium sulfate , calcium phosphate or calcium lactate ) . Only approx. 50% of the extracellular calcium is in a freely ionized and thus in a biologically active form. Symptoms of hypocalcemia do not appear until there is a lack of this ionized calcium component.

Daily requirement

DGE, ÖGE, SGE reference values

The DA-CH reference values ​​of the German Nutrition Society , the Austrian Nutrition Society and the Swiss Nutrition Society (2012); the maximum tolerable intake levels were obtained from the European Agency for Food Safety issued (European Food Safety Authority, EFSA) 2006:

Age Recommended intake
(mg / day)
Nutrient density
male (mg / MJ ) 1
Nutrient density
female (mg / MJ ) 1
Maximum tolerable
intake
(UL)
(mg / day)
Infant 0-4 months 2 220 mg 110 mg 116 mg n / a
Infant 4–12 months 330 mg 133 mg 138 mg n / a
1-4 years 600 mg 128 mg 136 mg n / a
4–7 years 750 mg 109 mg 121 mg n / a
7-10 years 900 mg 114 mg 127 mg n / a
10–13 years 1100 mg 117 mg 129 mg n / a
13-15 years 1200 mg 107 mg 128 mg n / a
15-19 years 1200 mg 113 mg 141 mg n / a
19-25 years 1000 mg 94 mg 123 mg 2500 mg
25–51 years 1000 mg 98 mg 128 mg 2500 mg
51–65 years 1000 mg 109 mg 135 mg 2500 mg
over 65 years 1000 mg 120 mg 145 mg 2500 mg
Pregnant women
under 19 years of age
1200 mg - ~ 109 mg 2500 mg
Pregnant women
over 19 years
1000 mg - 109 mg 2500 mg
Breastfeeding women
under 19 years of age
1200 mg - ~ 93 mg 2500 mg
Breastfeeding women
over 19 years
1000 mg - 93 mg 2500 mg
1Calculated for adolescents and adults with predominantly sedentary work ( physical activity level of 1.4)
2 This is an estimate

Food and Nutrition Board (US) benchmarks

The recommendations of the US Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies (November 2010):

Age Estimated requirement
(mg / day)
Recommended intake
(mg / day)
Maximum tolerable
intake
(UL)
(mg / day)
Infant 0–6 months n / a 200 mg 1000 mg
Infant 6-12 months n / a 260 mg 1500 mg
1-3 years 500 mg 700 mg 2500 mg
4-8 years 800 mg 1000 mg 2500 mg
9–13 years 1110 mg 1300 mg 3000 mg
14-18 years 1110 mg 1300 mg 3000 mg
19-30 years 800 mg 1000 mg 2500 mg
30–50 years 800 mg 1000 mg 2500 mg
50–70 years men 800 mg 1000 mg 2000 mg
50–70 years women 1000 mg 1200 mg 2000 mg
older than 70 years 1000 mg 1200 mg 2000 mg
14–18 years
pregnant / breastfeeding
1100 mg 1300 mg 3000 mg
19–50 years
pregnant / breastfeeding
800 mg 1000 mg 2500 mg

admission

Not all calcium that is absorbed by the food is in the stomach absorbed . Humans absorb around 30% of the calcium from food, but this percentage varies depending on the composition of the food. Other factors also influence calcium absorption. The efficiency of absorption decreases with increasing calcium intake. In growing infants and children, the resorption rate is up to 60%, as they need a lot of calcium for bone formation. The rate of absorption falls to 15 to 20% in adults, with the need for women increasing again during pregnancy.

Risk groups for insufficient calcium intake are young women, pregnant women , breastfeeding women and the elderly.

A sufficient supply of vitamin D 3 is a prerequisite for the body to be able to absorb calcium in larger quantities . The simultaneous supply of oxalic acid and phytic acid and their salts ( oxalates , phytates ) reduces calcium absorption. Calcium is excreted in the urine , whereby a high intake of proteins , table salt , coffee or alcohol increases the calcium excretion.

The specific amino acid profile - especially of sulfur-containing amino acids - determines the calciuretic ( promoting calcium excretion via the kidneys ) of dietary proteins. Sulphates , which are formed from such amino acids in the metabolism, increase the acidity of the urine, which means that larger amounts of calcium are excreted in the urine. Sulfur-containing amino acids can be found in food of animal origin as well as in food plants such as cereals .

Calcium sources

Approximate calcium content in mg per 100 g of food (edible portion):

Health risks

In contrast to people with healthy kidneys , a dialysis patient cannot excrete excess calcium in the urine , and the bones usually do not absorb the calcium supplied either . There is a risk that calcium will settle in blood vessels and soft tissues. Calcium carbonate , used as a phosphate binder , can contribute to cardiovascular calcification. A study carried out over two years in 2004 showed a steady correlation between the consumption of calcium carbonate and progressive hardening of the arteries in hemodialysis patients.

In 2010, Bolland et al. a. in the British Medical Journal a meta-analysis claiming that calcium supplements without cholecalciferol (vitamin D 3 ) increase the risk of heart attack by up to 30%. This effect should occur dose-dependently from a daily supplement of 500 mg calcium without vitamin D 3 . Also, strokes and deaths occurred in the calcium supplement group increased. This work has been criticized for its methodology. The drug commission of the German medical profession recognized in the von Bolland u. a. The data presented does not provide sufficient evidence of an increased risk of myocardial infarction due to the use of calcium supplements. In a statement, the commission also pointed out that the sole administration of calcium investigated in the meta-analysis to correct an osteoporotic metabolic disorder without additional administration of vitamin D 3 is not recommended in the current German guidelines . On the other hand, the benefit of the combined substitution of calcium and vitamin D 3 for the prevention of fractures is limited and depends on factors such as dietary calcium intake, vitamin D serum concentration, age, placement in a nursing home and the initial risk of fractures . There are no meaningful data to show that calcium supplementation is beneficial in people with normal calcium and vitamin D 3 supplies. On the other hand, negative effects such as an increased risk of kidney stones could be demonstrated. Calcium supplements could therefore not be generally recommended. Rather, risk groups should be identified who are likely to benefit from additional calcium administration. In the opinion of the commission, the total calcium intake (food plus supplement) should be 1000 to 1500 mg.

Studies from 2013 also indicate an increased mortality due to over-substitution of calcium. A Swedish study shows that women who were unnecessarily substituted with calcium, although sufficient calcium was ingested through their diet, had an increased mortality. Another study found that men had an increased cardiovascular risk from calcium substitution.

Two prospective cohort studies showed that the consumption of calcium doses> 2000 mg per day is associated with an increased risk of prostate cancer . Two other prospective cohort studies found no association for calcium doses of 1330 and 1840 mg per day. A deficient production of vitamin D 3 is suspected as the background for the increased risk . High calcium intake decreases the body's own cholecalciferol production , and preclinical studies have shown several potentially beneficial effects of the vitamin on prostate cancer. It is unclear to what extent calcium consumption in relation to fat consumption (from milk and milk products) contributes to the risk.

links

In compounds calcium occurs almost exclusively as a divalent cation with the oxidation state 2.

Oxides and hydroxides

Calcium oxide is a white crystalline substance that reacts with water while generating a lot of heat . It forms crystals in the sodium chloride - structure . Burnt lime , which is then slaked with water , is used in the construction industry as an admixture to mortar and plaster , as well as for the industrial production of sand-lime bricks . It is also a subordinate component of cement clinker . In chemistry , the substance is also used as a drying agent and for absorbing carbon dioxide .

Calcium peroxide is a strong oxidizing agent and has a medium oxidizing effect, as it releases oxygen when heated . It is often present as octahydrate , which loses the water of crystallization at around 130 ° C. The octahydrate has a tetragonal crystal structure in the space group P 4 / mcc (space group no. 124) . It is used as a drying accelerator for polysulfide elastomers , an antiseptic in toothpastes and chewing gum , as a stabilizer in the rubber industry, in dentistry , as a dough improver in the baking industry and as a seed disinfectant . Template: room group / 124

Calcium hydroxide is a colorless powder, which only slightly dissolves in water , whereby the solution reacts strongly basic . It consists of trigonal crystals with the polytype 2H of the crystal structure of the cadmium iodide type in the space group P 3 m 1 (space group no.164) . It is used for the production of mortar in construction , as a disinfectant , acid regulator in food and pesticides in fruit growing . Template: room group / 164

Halides

Calcium fluoride in the form of a purple fluorite

Calcium chloride forms colorless crystals in its pure form and is highly hygroscopic in an anhydrous state . It easily takes water from the environment, forming a hydrate - complex . Several crystalline hydrates are known. Due to its hygroscopicity, anhydrous calcium chloride is an important drying agent in the laboratory , for example in the desiccator , and in technical chemistry for gases and liquids . It is also used as de-icing salt , in concrete as a setting accelerator , as road salt , as an antifreeze , as a complexing agent , flavor enhancer and stabilizer in the food industry and as an electrolyte in sports drinks .

Calcium fluoride forms colorless crystals that are sparingly soluble in water , alcohol and dilute acids . It crystallizes in the cubic crystal system in the highly symmetrical crystal class 4 / m 3 2 / m ( cubic-hexakisoctahedral ) or the space group Fm 3 m (space group no. 225) . Naturally occurring calcium fluoride is called fluorite or fluorspar and is mostly colored yellow, green, blue or purple due to impurities. Template: room group / 225

Calcium bromide is a colorless solid that slowly turns yellow in air . Like calcium chloride and strontium chloride, it crystallizes in the calcium chloride structure, which is similar to the rutile structure .

Calcium iodide is a high-melting crystalline solid which crystallizes in a typical layer structure , the hexagonal cadmium iodide structure in the space group P 6 3 mc (space group no.186) . If calcium iodide hydrate comes into contact with air or light , it can absorb carbon dioxide or release iodine and, as a result, turns yellow. Template: room group / 186

Other inorganic compounds

Lime powder consists of calcium carbonate

Calcium carbonate is a colorless, crystalline solid . It is one of the most widespread compounds on earth, especially in the form of limestone , chalk , marble and sedimentary rocks . It occurs primarily in the form of the mineral calcite , which is one of the most common minerals in the earth's crust . Limestone is used in large quantities as a raw material for the building material - industry , as additive in the steel industry , as mineral fertilizer , as a feed lime , and as a mineral filler in various industrial use applications, such as in papers , paints , coatings , plaster , plastics and backside coatings of Carpets .

Calcium sulphate is a white solid that is sparingly soluble in water and decomposes at temperatures above 1200 ° C, producing calcium oxide and sulfur trioxide . It occurs naturally in the form of the minerals anhydrite , gypsum (Ca [SO 4 ] · 2H 2 O) and bassanite (Ca [SO 4 ] · ½H 2 O) in evaporites . It is used as a building material.

Calcium nitrate is a white, hygroscopic , oxidizing solid that is very easily soluble in water . It forms a series of hydrates . It is used as a fertilizer and as a component of cooling brines and of latex coagulating baths.

Calcium carbide (calcium acetylide) is in the pure state is a colorless, crystalline mass. There are two modifications , the tetragonal and a face-centered cubic modification of the pyrite type, which is formed by heating above 440 ° C. It is used as a starting material for chemical syntheses and for the production of calcium cyanamide - fertilizer , for the production of acetylene , in which desulfurization of iron , as a fuel in the production of steel and carbide used.

Organic compounds

Calcium gluconate is used as an acid regulator in the chemical industry but also in the food industry. It is added to foods as a complexing agent , acid regulator or stabilizer . It also has various medical uses.

Calcium stearate is the calcium salt of stearic acid and belongs to the lime soaps . It consists of a calcium ion and two long-chain stearate ions. It is used to produce so-called non-tox stabilizers for plastics , preferably in conjunction with zinc stearate , but also barium stearate or magnesium stearate . It is also used as a lubricant in pharmaceutical products and as a lubricant ( Stauffer grease ) in the paper and metal processing industry , as a water repellent for building materials and in sand processing.

See also

Web links

Wiktionary: Calcium  - explanations of meanings, word origins, synonyms, translations
Commons : Calcium  album with pictures, videos and audio files

Individual evidence

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