Calcium Facts – Atomic Number 20 and Element Symbol Ca

Calcium is the 20th element of the periodic table. These calcium facts contain chemical and physical data along with general information and history.

Element cell for Calcium

Calcium periodic table cell

Basic Calcium Facts

Name: Calcium

Atomic Number: 20

Element Symbol: Ca

Group: 2

Period: 4

Block: s

Element Family: Alkaline Earth

Atomic Mass: 40.078(4)

Electron Configuration: [Ar]4s2
Full: 1s22s22p63s23p64s(full)

Discovery: Sir Humphry Davy in 1808

Davy is well known for his electrolysis experiments. He would place his instrument in samples of various common chemicals and observe what collects at the electrodes. He isolated pure calcium from a paste of lime (calcium oxide) using a mercury electrode. An solid amalgam of calcium and mercury formed when current was applied. Davy then used chemical techniques to remove the mercury and solid calcium remained.

Name Origin: Calcium got its name from the Latin name for lime, calx.


Natural calcium is comprised of six isotopes: 40Ca, 42Ca, 43Ca, 44Ca, 46Ca, and 48Ca.
Five stable and nineteen radioactive isotopes exist ranging from 34Ca to 57Ca.

Calcium-40 is a stable isotope containing 20 neutrons. 96.941% of natural calcium is calcium-40. Calcium-40 is theorized to actually be a radioactive isotope with an extremely long half-life (~1021 years) based on its internal structure. No one has ever detected a decay of a calcium-40 atom.

Calcium-42 is a stable isotope containing 22 neutrons. 0.647% of natural calcium is calcium-42.

Calcium-43 is a stable isotope containing 23 neutrons. 0.135% of natural calcium is calcium-43.

Calcium-44 is a stable isotope containing 24 neutrons. 2.086% of natural calcium is calcium-44.

Calcium-46 is a stable isotope containing 26 neutrons. 0.004% of natural calcium is calcium-46.
As with calcium-40, the internal structure of the calcium-46 atom is theoretically unstable and could be radioactive. No one has ever observed the decay of a calcium-46 atom.

Calcium-48 is almost a stable isotope containing 28 neutrons. Calcium-48 has been observed to decay into titanium-48 by double β- decay. The half-life of this decay has been calculated to 3.338 x 1021 years. This decay makes calcium-48 the lightest isotope to undergo double β- decay. 0.187% of natural calcium is calcium-48.

Calcium Metal (Tomihahndorf)

Calcium Metal (Tomihahndorf)

Physical Data

Density:  1.54 g/cm3

Melting Point: 1115 K ​(842 °C, ​1548 °F)

Boiling Point: 1757 K ​(1484 °C, ​2703 °F)

State at 20ºC: Solid

Heat of Fusion: 8.54 kJ/mol

Heat of Vaporization: 154.7 kJ/mol

Molar Heat Capacity: 25.929 J/mol·K

Calcium atom

Electron shell configuration for calcium.

Atomic Data

Atomic Radius: 1.97 Å (empirical)

Covalent Radius: 1.76 Å

Van der Waals Radius:  2.31 Å

Electron Affinity: 2.369 kJ/mol

Electronegativity: 1.00

1st Ionization Energy: 589.83 kJ/mol

2nd Ionization Energy: 1145.447 kJ/mol

3rd Ionization Energy: 4912.368 kJ/mol

4th Ionization Energy: 5876.92 kJ/mol

5th Ionization Energy: 8153 kJ/mol

6th Ionization Energy: 10495.68 kJ/mol

7th Ionization Energy: 12272.9 kJ/mol

8th Ionization Energy: 14206.5 kJ/mol

Oxidation States: +2 (common), +1, -1 (uncommon)

Calcium Flame Test

Calcium flame test. Credit: Herge/Creative Commons

Fun Calcium Facts

  • Calcium is a soft silvery metal at room temperature. Left alone, it will quickly oxidize in air forming a dull grey patina.
  • Calcium burns with a bright orange-red flame in a flame test.
  • Calcium is used in fireworks to add orange color.
  • Calcium is the fifth most abundant element in the human body. Nearly all the calcium in your body is in your teeth and bones.
  • Vitamin D is vital for the absorption of calcium in your body.
  • Calcium is the fifth most abundant element in the Earth’s crust, accounting for approximately 4.1% by mass.
  • Calcium is not found native in nature. It is always part of another compound.
  • Sea creature shells are mostly calcium carbonate.
  • Calcium can be found abundantly in limestone (calcium carbonate), gypsum (calcium sulfate), fluorite (calcium fluoride) and apatite (calcium-chloro-( or fluoro-) phosphate.
  • Calcium is produced commercially by heating lime (calcium oxide) with aluminum in a low pressure environment.
  • Calcium is used for making cement, making cheese, removing nonmetallic impurities from alloys, and as a reduction agent in the preparation of other metals.
  • Calcium was known to exist for centuries before Davy identified it as an element.

Learn more about elements on the periodic table.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.