Element 20 · Alkaline earth metal
Calcium (Ca) — Element 20
Latin calx — lime
Calcium (Ca) is an alkaline earth metal in Period 4, Group 2 of the periodic table with atomic number 20, standard atomic weight 40.078 u, and ground-state electron configuration [Ar] 4s². At standard temperature and pressure it is classified as a solid with 2 valence electrons and common oxidation states +2.
Bones, cement, steelmaking
What are the atomic properties and physical constants of Calcium?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 20
- Standard atomic mass
- 40.078 u
- Chemical family
- Alkaline earth metal
- Ground-state configuration
- [Ar] 4s²
- Electrons per shell
- 2, 8, 8, 2
- Valence electrons
- 2
- Common ion charges / oxidation states
- +2
- Phase at STP
- Solid
- Pauling electronegativity
- 1.00 Pauling
- First ionization energy
- 590 kJ/mol
- Atomic radius
- 194 pm
- Melting point
- 842 °C
- Boiling point
- 1,484 °C
- Discovery year
- 1808
- Table coordinate
- Period 4, Group 2
- Radioactivity
- Has stable isotope(s)
How are electrons arranged across Calcium’s shells?
A neutral Calcium atom contains 20 electrons distributed across 4 occupied principal energy shells ([Ar] 4s²). The table below compares Calcium’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in Ca | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 8 e⁻ | 18 e⁻ |
| n = 4 | N | 2 e⁻ | 32 e⁻ |
Frequently Asked Questions about Calcium (Ca)
What is the atomic mass and atomic number of Calcium (Ca)?
Calcium (Ca) has atomic number Z = 20 (20 protons in its nucleus) and an IUPAC standard atomic weight of 40.078 u. It sits in Period 4, Group 2 and is classified as an alkaline earth metal.
What is the ground-state electron configuration of Calcium?
The neutral ground-state electron configuration of Calcium (Z = 20) is [Ar] 4s². Across its 4 occupied principal shells (n = 1 to n = 4), the electrons per shell are 2, 8, 8, 2, with 2 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Calcium?
Calcium commonly forms +2 oxidation states or ion charges in compounds. Its Pauling electronegativity is 1.00 and its first ionization energy is 590 kJ/mol.
When was Calcium discovered and what is it used for?
Calcium was discovered in 1808 (Latin calx — lime). Bones, cement, steelmaking
How does Calcium compare to neighboring elements?
Other alkaline earth metal elements: