ElementsWhat is calcium?
Calcium is a silvery metal, but people meet it mostly in its compounds: limestone, chalk, marble, shells, bones and teeth. It is the fifth most common element in the Earth's crust.
What is calcium used for?
Cement and concrete, plaster, lime for steel making and for soil, and calcium tablets and fortified foods.
Where the name comes from
From the Latin word calx, meaning lime.
Key facts
- Symbol
- Ca
- Atomic number
- 20
- Atomic mass
- 40.08 u
- Family
- Alkaline earth metal
- Period
- 4
- Group
- 2
- Block
- s
- State at room temperature
- Solid
- Melting point
- 841.9 °C (1,115 K, 1,547 °F)
- Boiling point
- 1,484 °C (1,757 K, 2,703 °F)
- Density
- 1.54 g/cm³
- Electrons per shell
- 2, 8, 8, 2
- Electron configuration
- [Ar]4s2
- Common oxidation states
- +2
- Electronegativity (Pauling)
- 1
- First ionisation energy
- 6.113 eV
- Electron affinity
- no value
- Atomic radius (van der Waals)
- 231 pm
- Discovered
- 1808
Place in the periodic table
Calcium is element number 20. It sits in period 4 (row 4) of the periodic table, in group 2 (column 2), and belongs to the s-block. Just before it comes potassium (19), and just after it comes scandium (21). In the same column, magnesium is above it and strontium is below it. Elements in one column tend to behave alike.
Family: Alkaline earth metals.
Physical properties
At room temperature calcium is a solid. It melts at 841.9 °C and boils at 1,484 °C, so it stays liquid over a range of 642 degrees. Its density is 1.54 grams per cubic centimetre, so a one-litre block would weigh about 1.54 kilograms. By density it ranks 81st among the 96 elements with a measured value.
Inside the atom
An atom of calcium has 20 protons in its nucleus and, when neutral, 20 electrons around it. The electrons are arranged in 4 shells: 2, 8, 8, 2. The outermost shell holds 2 electrons. Written in full, the electron configuration is [Ar]4s2.
Its electronegativity on the Pauling scale is 1. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 6.113 electronvolts (about 590 kilojoules per mole). One mole of calcium weighs 40.08 grams, so a single gram contains about 1.50 × 1022 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains calcium with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.