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Calcium (Ca)

Calcium is a chemical element of the periodic table with chemical symbol Ca and atomic number 20 with an atomic weight of 40.0784 u and is classed as alkaline earth metal and is part of group 3 (scandium group). Calcium is solid at room temperature.

Calcium in the periodic table

Atomic number20
Group3 (Scandium group)
ClassificationAlkaline Earth Metal
Color Silver
Number of protons20 p+
Number of neutrons20 n0
Number of electrons20 e-
From Wikipedia, the free encyclopediaCalcium is a chemical element with symbol Ca and atomic number 20. Calcium is a soft gray alkaline earth metal, fifth-most-abundant element by mass in the Earth's crust. The ion Ca2+ is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate.

Physical properties

Phase at STPSolid
Density1.55 g/cm3
Atomic weight40.0784 u

Thermal properties

Melting point1115 K
841.85 °C
1547.33 °F
Boiling point1757 K
1483.85 °C
2702.93 °F
Heat of vaporization154.67 kJ/mol

Atomic properties

Electronegativity (Pauling Scale)1
Electron affinity2.37 kJ/mol
Oxidation states+1, +2
(a strongly basic oxide)
Ionization energies
  1. 589.8 kJ/mol
  2. 1145.4 kJ/mol
  3. 4912.4 kJ/mol
  4. 6491 kJ/mol
  5. 8153 kJ/mol
  6. 10496 kJ/mol
  7. 12270 kJ/mol
  8. 14206 kJ/mol
  9. 18191 kJ/mol
  10. 20385 kJ/mol
  11. 57110 kJ/mol
  12. 63410 kJ/mol
  13. 70110 kJ/mol
  14. 78890 kJ/mol
  15. 86310 kJ/mol
  16. 94000 kJ/mol
  17. 104900 kJ/mol
  18. 111711 kJ/mol
  19. 494850 kJ/mol
  20. 527762 kJ/mol

Electron configuration for calcium

Electron configuration
Shorthand configuration
[Ar] 4s2
Electron configuration
Full configuration
1s2 2s2 2p6 3s2 3p6 4s2
Electron configuration chart
Electrons per shell2, 8, 8, 2
Valence electrons 2
Valency electrons 2
Bohr model
CalciumElectron shell for Calcium, created by Injosoft ABCa
Figure: Shell diagram of Calcium (Ca) atom.
Orbital Diagram

The history of Calcium

Discovery and first isolationHumphry Davy (1808)
Discovery of calcium
Calcium compounds were known for millennia, although their chemical makeup was not understood until the 17th century. Lime as a building material and as plaster for statues was used as far back as around 7000 BC. Vitruvius, a Roman architect, noted that the lime that resulted was lighter than the original limestone, attributing this to the boiling of the water. In 1755, Joseph Black proved that this was due to the loss of carbon dioxide, which as a gas had not been recognised by the ancient Romans. In 1789, Antoine Lavoisier suspected that lime might be an oxide of a fundamental chemical element. Calcium, along with its congeners magnesium, strontium, and barium, was first isolated by Humphry Davy in 1808. Following the work of Jöns Jakob Berzelius and Magnus Martin af Pontin on electrolysis.


List of unique identifiers for Calcium in various chemical registry databases
CAS Number7440-70-2
ChemSpider ID4573905
EC number231-179-5
PubChem CID Number5460341