Calcium (Ca)
[Ar] 4s². 0 unpaired electrons, period 4, group 2, s block.
Element or ion
Type a symbol, a name or an atomic number, add a charge such as Fe3+ or Cl-, or tap an element in the table. Orbitals fill from m = −l up, spin +½ first.
CaCalcium, Z = 20, 40.078 u
[Ar] 4s2
In full: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
- Blocks block
- Period4
- Group2
- Valence2
- Unpaired0
- MagneticDia
Last electron 4s
- n4shell
- l0s subshell
- m0orbital
- s−½spin down
Step by step
- Calcium has 20 electrons.
- Fill in (n + l) order: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s².
- Write the subshells in order of n: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s².
- Replace the argon core with [Ar]: [Ar] 4s².
Calcium (Ca): the numbers
| Atomic number | 20 |
|---|---|
| Atomic mass | 40.078 u |
| Period | 4 |
| Group | 2 |
| Block | s block |
| Valence electrons | 2 |
| Unpaired electrons | 0 |
| Magnetic | diamagnetic |
| Last electron | 4s: n = 4, l = 0, m = 0, s = −1/2 |
Calcium (Ca): quick answers
What is the electronic configuration of calcium?
Calcium has 20 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s², or [Ar] 4s² in short.
How many unpaired electrons does calcium have?
Calcium has 0 unpaired electrons, so it is diamagnetic. Put one electron in each box of a subshell before pairing (Hund’s rule) to see them.
What are the quantum numbers of the last electron of calcium?
The last electron goes into 4s: n = 4, l = 0, m = 0, s = −1/2. Orbitals fill from m = −l up, spin +½ first.