Calcium
Calcium is a chemical element with symbol Ca and atomic number 20. Calcium is a soft gray alkaline earth metal, fifth-most-abundant element by mass in the Earth's crust. The ion Ca2+ is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate.
A stylized shell model. Electrons are quantum objects, not particles following these literal paths. Sizes and motion are illustrative.
18 is the [Ar] core total across three shells.
At a glance
- Atomic number
- 20
- Atomic mass
- 40.0784 u
- Phase
- Solid
- Density
- 1.55 g/cm³
- Melting point
- 1,115 K
- Boiling point
- 1,757 K
- First ionization energy
- 589.8 kJ/mol
- Electronegativity
- 1
- Electron affinity
- 2.37 kJ/mol
- Molar heat capacity
- 25.929 J/(mol·K)
- Period
- 4
- Appearance
- Unavailable
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.