Periodic table / Alkaline earth metals
20Calcium
Calcium is an alkaline earth metal in group 2, period 4. At 25 °C it is a solid.
- Symbol
- Ca
- Atomic number
- 20 protons in the nucleus
- Standard atomic weight
- 40.078 ± 0.004Some geological samples have an unusual isotope mix, so their atomic weight can fall outside this range.
- Electron configuration
- [Ar] 4s2
- Electrons in each shell
- 2, 8, 8, 2
- Group, period, block
- 2, 4, s
- Family
- Alkaline earth metals
- State at 25 °C
- solid
- Electronegativity
- 1 (Pauling scale)
- First ionisation energy
- 589.8 kJ/mol (6.113154921 eV)
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Where these numbers come from
Atomic weight: IUPAC CIAAW, abridged standard atomic weights 2024. Electron configuration and ionisation energy: NIST Atomic Spectra Database. Family, state and electronegativity: PubChem. See Sources. Melting points, boiling points and densities are left out for now: published values differ between sources, and we will add them once each has been checked.