Calcium (Ca): Electron Configuration, Properties and Uses
Calcium (Ca): Electron Configuration, Properties and Uses
Electron configuration [Ar] 4s2 · group 2 · period 4 · Ar 40.078
Calcium data
- Atomic number
- 20
- Relative atomic mass
- 40.078
- Group
- 2
- Period
- 4
- Block
- s
- Category
- Alkaline earth metal
- Electron configuration
- [Ar] 4s2
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2
- Electrons per shell
- 2, 8, 8, 2 (K L M N)
- Valence electrons
- 2
- Electronegativity (Pauling)
- 1
- First ionisation energy
- 6.113 eV
- Atomic radius (van der Waals)
- 231 pm
- State at room temperature
- Solid
- Melting point
- 842 °C
- Boiling point
- 1484 °C
- Density
- 1.54 g/cm³
- Common oxidation states
- +2
- Discovered
- ancient times
Source: PubChem (NIH, accessed 13 Nov 2026); atomic mass: IUPAC standard atomic weight.
Electron shell diagram
K 2 · L 8 · M 8 · N 2
Orbital diagram (outer electrons)
About calcium
Calcium, symbol Ca, is element number 20 in the periodic table. It is an alkaline earth metal in group 2, period 4, s-block. Calcium has been known and used since ancient times. Calcium is a solid at room temperature, melting at 842 °C and boiling at 1484 °C.
Calcium electron configuration
The electron configuration of calcium is 1s2 2s2 2p6 3s2 3p6 4s2, or in short [Ar] 4s2. Its electrons occupy 4 shells: K = 2, L = 8, M = 8, N = 2. Calcium has 2 valence electrons in the N shell (4s2), which is why it sits in group 2. When it forms cations, electrons leave the outermost subshell first: Ca2+ = [Ar] (like argon).
Filling order: 1s2(2) → 2s2(4) → 2p6(10) → 3s2(12) → 3p6(18) → 4s2(20)
Uses of calcium
Well-known applications of calcium include cement and lime, bones and teeth, calcium carbonate for paper and antacids, and as a reducing agent in metal production. For research and analysis you can browse calcium compounds in the AMI Scientific catalogue.
Safety
Calcium metal reacts with water to release hydrogen, though less violently than the alkali metals. Always read the safety data sheet (SDS) before working with a chemical.
Other elements in group 2
Frequently asked questions
What is the electron configuration of calcium?
The electron configuration of calcium (Ca, atomic number 20) is 1s2 2s2 2p6 3s2 3p6 4s2, or [Ar] 4s2 in short. By shell: 2, 8, 8, 2.
How many valence electrons does calcium have?
Calcium has 2 valence electrons.
Which group and period is calcium in?
Calcium is in group 2, period 4, s-block.
What is the atomic mass of calcium?
The relative atomic mass of calcium is 40.078. Use it to calculate molar mass with the molar mass calculator.
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