Calcium


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Calcium (Wikipedia)

Calcium, 20Ca
Calcium unter Argon Schutzgasatmosphäre.jpg
Calcium
Appearancedull gray, silver; with a pale yellow tint
Standard atomic weight Ar, std(Ca)40.078(4)
Calcium in the periodic table
HydrogenHelium
LithiumBerylliumBoronCarbonNitrogenOxygenFluorineNeon
SodiumMagnesiumAluminiumSiliconPhosphorusSulfurChlorineArgon
PotassiumCalciumScandiumTitaniumVanadiumChromiumManganeseIronCobaltNickelCopperZincGalliumGermaniumArsenicSeleniumBromineKrypton
RubidiumStrontiumYttriumZirconiumNiobiumMolybdenumTechnetiumRutheniumRhodiumPalladiumSilverCadmiumIndiumTinAntimonyTelluriumIodineXenon
CaesiumBariumLanthanumCeriumPraseodymiumNeodymiumPromethiumSamariumEuropiumGadoliniumTerbiumDysprosiumHolmiumErbiumThuliumYtterbiumLutetiumHafniumTantalumTungstenRheniumOsmiumIridiumPlatinumGoldMercury (element)ThalliumLeadBismuthPoloniumAstatineRadon
FranciumRadiumActiniumThoriumProtactiniumUraniumNeptuniumPlutoniumAmericiumCuriumBerkeliumCaliforniumEinsteiniumFermiumMendeleviumNobeliumLawrenciumRutherfordiumDubniumSeaborgiumBohriumHassiumMeitneriumDarmstadtiumRoentgeniumCoperniciumNihoniumFleroviumMoscoviumLivermoriumTennessineOganesson
Mg

Ca

Sr
potassiumcalciumscandium
Atomic number (Z)20
Groupgroup 2 (alkaline earth metals)
Periodperiod 4
Blocks-block
Element category  Alkaline earth metal
Electron configuration[Ar] 4s2
Electrons per shell2, 8, 8, 2
Physical properties
Phaseat STPsolid
Melting point1115 K ​(842 °C, ​1548 °F)
Boiling point1757 K ​(1484 °C, ​2703 °F)
Density (near r.t.)1.55 g/cm3
when liquid (at m.p.)1.378 g/cm3
Heat of fusion8.54 kJ/mol
Heat of vaporisation154.7 kJ/mol
Molar heat capacity25.929 J/(mol·K)
Vapour pressure
P (Pa)1101001 k10 k100 k
at T (K)8649561071122714431755
Atomic properties
Oxidation states+1,+2 (a strongly basic oxide)
ElectronegativityPauling scale: 1.00
Ionisation energies
  • 1st: 589.8 kJ/mol
  • 2nd: 1145.4 kJ/mol
  • 3rd: 4912.4 kJ/mol
  • (more)
Atomic radiusempirical: 197 pm
Covalent radius176±10 pm
Van der Waals radius231 pm
Color lines in a spectral range
Spectral lines of calcium
Other properties
Natural occurrenceprimordial
Crystal structureface-centred cubic (fcc)
Face-centered cubic crystal structure for calcium
Speed of sound thin rod3810 m/s (at 20 °C)
Thermal expansion22.3 µm/(m·K) (at 25 °C)
Thermal conductivity201 W/(m·K)
Electrical resistivity33.6 nΩ·m (at 20 °C)
Magnetic orderingdiamagnetic
Magnetic susceptibility+40.0·10−6 cm3/mol
Young's modulus20 GPa
Shear modulus7.4 GPa
Bulk modulus17 GPa
Poisson ratio0.31
Mohs hardness1.75
Brinell hardness170–416 MPa
CAS Number7440-70-2
History
Discovery and first isolationHumphry Davy (1808)
Main isotopes of calcium
Iso­topeAbun­danceHalf-life(t1/2)Decay modePro­duct
40Ca96.941%stable
41Catrace9.94×104 yε41K
42Ca0.647%stable
43Ca0.135%stable
44Ca2.086%stable
45Casyn162.6 dβ45Sc
46Ca0.004%stable
47Casyn4.5 dβ47Sc
γ
48Ca0.187%6.4×1019 yββ48Ti
| references

Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The name derives from Latin calx "lime", which was obtained from heating limestone.

Some calcium compounds were known to the ancients, though their chemistry was unknown until the seventeenth century. Pure calcium was isolated in 1808 via electrolysis of its oxide by Humphry Davy, who named the element. Calcium compounds are widely used in many industries: in foods and pharmaceuticals for calcium supplementation, in the paper industry as bleaches, as components in cement and electrical insulators, and in the manufacture of soaps. On the other hand, the metal in pure form has few applications due to its high reactivity; still, in small quantities it is often used as an alloying component in steelmaking, and sometimes, as a calcium–lead alloy, in making automotive batteries.

Calcium is the most abundant metal and the fifth-most abundant element in the human body. As electrolytes, calcium ions play a vital role in the physiological and biochemical processes of organisms and cells: in signal transduction pathways where they act as a second messenger; in neurotransmitter release from neurons; in contraction of all muscle cell types; as cofactors in many enzymes; and in fertilization. Calcium ions outside cells are important for maintaining the potential difference across excitable cell membranes, protein synthesis, and bone formation.

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