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Calcium

Element 20 · Alkaline earth metal

Specimen

Atomic number
20
Atomic mass
40.078
State at room temperature
Solid
Melting point
841.9 °C
Boiling point
1,484 °C
Density
1.54 g/cm³
Discovered
Ancient

Atomic mass from IUPAC.1 Other physical data from PubChem.2

Can I eat it?

In food and water
Your body needs it. Calcium is a nutrient. About 99% of the calcium in the body is in bones and teeth. When the diet has too little calcium, the body takes it from bone. 3

See every element.

The atom

Ca
ShellElectrons
1 (K) 2
2 (L) 8
3 (M) 8
4 (N) outermost 2
Total20

Configuration [Ar] 4s²

4s ↑ ↓
A shell diagram: each ring is an electron shell and each dot is one electron. The nucleus holds 20 protons. The outermost shell is shown in red. Electrons do not travel on rings: they fill orbitals, regions where an electron is likely to be found. The boxes are those orbitals for the electrons outside the Ar core, with one arrow per electron.

Related elements

Group 2
Be Beryllium Mg Magnesium Sr Strontium Ba Barium Ra Radium

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Sources

  1. 1

    IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2024. Abridged Standard Atomic Weights 2024 .

    The atomic mass shown for the 84 elements that have a standard atomic weight.

  2. 2

    National Center for Biotechnology Information (PubChem), 2026. Periodic Table of Elements .

    Electron configuration, melting and boiling points, density and discovery year for all 118 elements.

  3. 3

    European Food Safety Authority (EFSA), 2017. Dietary Reference Values for nutrients. Summary report (amended 2019) .

    Summaries of the EFSA NDA Panel opinions on each vitamin and mineral, section 4 (minerals) and section 5 (cobalamin).

    • approximately 99% of total body calcium is found in bones and teeth
    • If the dietary supply of calcium is insufficient to meet physiological requirements, calcium is resorbed from the skeleton
  4. 4

    National Institute of Standards and Technology (NIST), 2026. Atomic Weights and Isotopic Compositions for All Elements .

    Isotopic composition of each element; the most abundant isotope sets the neutron count in the nucleus view.