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Calcium,  20Ca
Calcium under argon atmosphere.jpg
Calcium metal under argon.
General properties
Name, symbol Calcium, Ca
Appearance Silvery-gray
Calcium in the periodic table


Atomic number 20
Standard atomic weight (Ar) 40.078(4)
Group, block (alkaline earth metals); s-block
Period period 4
Electron configuration [Ar] 4s2
per shell
2, 8, 8, 2
Physical properties
Phase Solid
Melting point 1115 K ​(842 °C, ​1548 °F)
Boiling point 1757 K ​(1484 °C, ​2703 °F)
Density near r.t. 1.55 g/cm3
when liquid, at  1.378 g/cm3
Heat of fusion 8.54 kJ/mol
Heat of 154.7 kJ/mol
Molar heat capacity 25.929 J/(mol·K)
Atomic properties
Oxidation states +2, +1 ​(a strongly basic oxide)
Electronegativity Pauling scale: 1.00
energies 1st: 589.8 kJ/mol
2nd: 1145.4 kJ/mol
3rd: 4912.4 kJ/mol
Atomic radius empirical: 197 pm
Covalent radius 176±10 pm
Van der Waals radius 231 pm
Crystal structure ​Face-centred cubic (fcc)
Speed of sound thin rod 3810 m/s (at 20 °C)
Thermal expansion 22.3 µm/(m·K) (at 25 °C)
Thermal conductivity 201 W/(m·K)
Electrical resistivity 33.6·10-9 Ω·m (at 20 °C)
Magnetic ordering Diamagnetic
Young's modulus 20 GPa
Shear modulus 7.4 GPa
Bulk modulus 17 GPa
Poisson ratio 0.31
Mohs hardness 1.75
Brinell hardness 170–416 MPa
CAS Registry Number 7440-70-2
Discovery and first isolation Humphry Davy (1808)
· references

Calcium is a chemical element with symbol Ca and atomic number 20. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust.



Calcium is reactive towards air but is often kept in a sealed container as opposed to under oil as its oxidation is not excessively rapid. As pellets or turnings, the metal can be difficult to ignite, more so even than magnesium turnings, but when lit the metal burns in air with a brilliant red light, producing calcium oxide.

Calcium reacts with the usually inert nitrogen, forming calcium nitride. If a container of calcium is left open in a glove box full of nitrogen, the metal will quickly be ruined.

Calcium produces hydrogen on contact with water, at a noticeably slower rater than all the alkali metals when in the same from but powder calcium is much more common than any alkali metal powders, and the increased surface area of the metal produces a rapid reaction. Part of the reason for the slowness of the calcium–water reaction is a result of the metal being partly protected by insoluble white calcium hydroxide. In acids where the calcium salt is soluble, the metal reacts vigorously.

At very high temperatures (usually in an electric arc furnace) the metal reacts with carbon to produce the useful calcium carbide.


Calcium is a soft for a metal (though harder than lead, it can be cut with a knife with difficulty). It is a silvery metallic element with a density of 1.55 g/cm3. Calcium has the lowest density of the alkaline earth metals; magnesium (specific gravity 1.74) and beryllium (1.84) are denser though lighter in atomic mass. From strontium onward, the alkali earth metals become denser with increasing atomic mass.


Calcium can be bought at Gallium Source.

As a reducing agent, it suffers some of the stigma and restrictions sodium does because it can be used in the manufacture of illicit drugs. In Australia, purchasing calcium metal requires an EUD.


Preparing calcium metal is not easy or economical for the amateur chemist. It can be extracted by electrolysis from a fused salt like calcium chloride. Once produced, it rapidly forms a gray-white oxide and nitride coating when exposed to air.




Compared with other metals, the calcium ion and most calcium compounds have low toxicity. This is not surprising given the very high natural abundance of calcium compounds in the environment and in organisms. Acute calcium poisoning is rare, and difficult to achieve unless calcium compounds are administered intravenously.

Calcium metal is hazardous because of it reacts violently with water and acids. Calcium metal is found in some drain cleaners, where it functions to generate heat and calcium hydroxide that saponifies the fats and liquefies the proteins (e.g., hair) that block drains. When swallowed calcium metal has the same effect on the mouth, esophagus and stomach, and can be fatal.


Large pieces of calcium metal can be stored in dry air without any severe degradation, as noted by many chemists. Turnings and calcium powder is much more reactive. Like all air-sensitive materials, calcium must be stored in sealed containers or glass ampoules, in an inert atmosphere (such as argon). It can also be stored in mineral oil.


Calcium metal can be neutralized by slowly dissolving it in water or simply leaving it in wet air, which causes it into calcium oxide, hydroxide and finally carbonate (or sulfate/nitrate, depending on the quality of air). Granular Ca metal degrades much faster than bulk metal.

As calcium compounds are abundant in the environment and pose no toxicity, no special treatment is required to dispose of them. However it is advised to avoid dumping the poorly soluble ones down the drain as they might build up and clog the pipes.


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