Calcium Facts - Ca or Atomic Number 20

Chemical and Physical Properties of Calcium

Calcium is a metal. It readily oxidizes in air. Because it makes up such a large part of the skeleton, about one-third of the mass of human body comes from calcium, after water has been removed.
Calcium is a metal. It readily oxidizes in air. Because it makes up such a large part of the skeleton, about one-third of the mass of human body comes from calcium, after water has been removed. Science Picture Co / Getty Images

Calcium is silver to gray solid metal that develops a pale yellow tint. It is element atomic number 20 on the periodic table with the symbol Ca. Unlike most transition metals, calcium and its compounds exhibit a low toxicity. The element is essential for human nutrition. Take a look at calcium periodic table facts and learn about the element's history, uses, properties, and sources.

Calcium Basic Facts

Symbol: Ca
Atomic Number: 20
Atomic Weight: 40.078
Classification: Alkaline Earth
CAS Number: 7440-701-2

Calcium Periodic Table Location

Group: 2
Period: 4
Block: s

Calcium Electron Configuration

Short Form: [Ar]4s2
Long Form: 1s22s22p63s23p64s2
Shell Structure: 2 8 8 2

Calcium Discovery

Discovery Date: 1808
Discoverer: Sir Humphrey Davy [England]
Name: Calcium derives its name from the Latin 'calcis' which was the word for lime (calcium oxide, CaO) and limestone (calcium carbonate, CaCO3)
History: The Romans prepared lime in the first century, but the metal was not discovered until 1808. Swedish chemist Berzelius and Swedish court physician Pontin created an amalgam of calcium and mercury by electrolyzing lime and mercury oxide. Davy managed to isolate pure calcium metal from their amalgam.

Calcium Physical Data

State at room temperature (300 K): Solid
Appearance: fairly hard, silvery white metal
Density: 1.55 g/cc
Specific Gravity: 1.55 (20 °C)
Melting Point: 1115 K
Boiling Point: 1757 K
Critical Point: 2880 K
Heat of Fusion: 8.54 kJ/mol
Heat of Vaporization: 154.7 kJ/mol
Molar Heat Capacity: 25.929 J/mol·K
Specific Heat: 0.647 J/g·K (at 20 °C)

Calcium Atomic Data

Oxidation States: +2 (most common), +1
Electronegativity: 1.00
Electron Affinity: 2.368 kJ/mol
Atomic Radius: 197 pm
Atomic Volume: 29.9 cc/mol
Ionic Radius: 99 (+2e)
Covalent Radius: 174 pm
Van der Waals Radius: 231 pm
First Ionization Energy: 589.830 kJ/mol
Second Ionization Energy: 1145.446 kJ/mol
Third Ionization Energy: 4912.364 kJ/mol

Calcium Nuclear Data

Number of Naturally Occurring Isotopes: 6
Isotopes and % Abundance: 40Ca (96.941), 42Ca (0.647), 43Ca (0.135), 44Ca (2.086), 46Ca (0.004) and 48Ca (0.187)

Calcium Crystal Data

Lattice Structure: Face-Centered Cubic
Lattice Constant: 5.580 Å
Debye Temperature: 230.00 K

Calcium Uses

Calcium is essential for human nutrition. Animals skeletons get their rigidity primarily from calcium phosphate. The eggs of birds and shells of mollusks are comprised of calcium carbonate. Calcium is also necessary for plant growth. Calcium is used as a reducing agent when preparing metals from their halogen and oxygen compounds; as a reagent in purification of inert gases; to fix atmospheric nitrogen; as a scavenger and decarbonizer in metallurgy; and for making alloys. Calcium compounds are used in making lime, bricks, cement, glass, paint, paper, sugar, glazes, as well as for many other uses.

Miscellaneous Calcium Facts

  • Calcium is the 5th most abundant element in the Earth's crust, making up 3.22% of the earth, air, and oceans.
  • Calcium is not found free in nature, but calcium compounds are common. Some of the most common compounds found on Earth are limestone (calcium carbonate - CaCO3), gypsum (calcium sulfate - CaSO4·2H2O), fluorite (calcium fluoride - CaF2) and apatite (calcium fluorophosphate - CaFO3P or calcium chlorophosphate - CaClO3P)
  • The top three countries that produce calcium are China, United States and India.
  • Calcium is the main component of teeth and bones. However, too much calcium can lead to kidney stones or artery calcification.
  • Calcium is the fifth most abundant element in the human body. Approximately one third of the mass of the human body is calcium after all water is removed.
  • Calcium burns with a dark red color in a flame test.
  • Calcium is used in fireworks to deepen the color. Calcium salts are used to produce orange in fireworks.
  • Calcium metal is soft enough to cut with a knife, although somewhat harder than the metal lead.
  • People and other animals can often taste the calcium ion. People report is as contributing a mineral, sour, or salty flavor.
  • Calcium metal reacts exothermically with water or acid. Skin contact with calcium metal can cause irritation, corrosion, and chemical burns. Ingesting or inhaling calcium metal can be fatal due to the burns it can produce.


  • Hluchan, Stephen E.; Pomerantz, Kenneth (2006) "Calcium and Calcium Alloys". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH, doi:10.1002/14356007.a04_515.pub2
  • Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
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Your Citation
Helmenstine, Anne Marie, Ph.D. "Calcium Facts - Ca or Atomic Number 20." ThoughtCo, Feb. 16, 2021, Helmenstine, Anne Marie, Ph.D. (2021, February 16). Calcium Facts - Ca or Atomic Number 20. Retrieved from Helmenstine, Anne Marie, Ph.D. "Calcium Facts - Ca or Atomic Number 20." ThoughtCo. (accessed May 31, 2023).