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Calcium,  20Ca
Template:Infobox element/symbol-to-top-image/alt
General properties
Appearancedull gray, silver; with a pale yellow tint
Standard atomic weight (Ar, standard)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 shell
2, 8, 8, 2
Physical properties
Phase at STPCa: Solid
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 vaporization154.7 kJ/mol
Molar heat capacity25.929 J/(mol·K)
Vapor 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
Ionization 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 occurrenceCa: Primordial
Crystal structureface-centered 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 (1/2)Decay modePro­duct
40Ca96.941%stable
41Catrace1.03×105 yε41K
42Ca0.647%stable
43Ca0.135%stable
44Ca2.086%stable
45Casyn162.7 dβ45Sc
46Ca0.004%stable
47Casyn4.5 dβ47Sc
γ
48Ca0.187%6.4×1019 yββ48Ti
| references
Very pure calcium metal, not corroded
Calcium metal in air, corroded

Calcium is a chemical element. Its symbol on the periodic table (a list of all the elements) is Ca. Its atomic number is 20. (The atomic number says where Calcium sits in the periodic table.) It has 20 protons and 20 electrons (if is an atom, see ion). The most common isotopes are Ca-40 and Ca-44. Its mass number is about 40.08.Calcium is very important in the human body, for making bones and for other purposes.

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