What is the electron configuration of calcium?

Calcium (Ca, Z=20) has the ground-state electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 4s². The 20 electrons fill six subshells across four principal energy levels.

What is the noble-gas shorthand for calcium?

The condensed (noble-gas) notation is [Ar] 4s², where [Ar] represents the filled 1s² 2s² 2p⁶ 3s² 3p⁶ core shared with argon (18 electrons).

Why does calcium form a +2 ion?

Calcium loses its two 4s valence electrons to form Ca²⁺, which achieves the stable [Ar] noble-gas core (1s² 2s² 2p⁶ 3s² 3p⁶). The energy needed to remove a third electron (from the 3p subshell) is far too high, so +2 is the only common oxidation state.

How many valence electrons does calcium have?

Calcium has 2 valence electrons, both in the 4s subshell. This is characteristic of all Group 2 alkaline earth metals.

What block and period is calcium in?

Calcium is in Period 4, Group 2 (IIA), and belongs to the s-block of the periodic table, since its outermost electrons are in the 4s subshell.

Is calcium paramagnetic or diamagnetic?

Calcium is diamagnetic. Both 4s electrons are spin-paired in the single 4s orbital, leaving no unpaired electrons. Diamagnetic substances are weakly repelled by a magnetic field.

What is the electron configuration of Ca²⁺?

The Ca²⁺ ion has the configuration 1s² 2s² 2p⁶ 3s² 3p⁶, identical to argon (Ar). It is isoelectronic with the noble gas argon, with 18 electrons total.

Calcium Electron Configuration

Name: Calcium Electron Configuration
Availability: InStock
Author: Nham Vu

Interactive reference for calcium's electron configuration (1s² 2s² 2p⁶ 3s² 3p⁶ 4s²), orbital diagram, quantum numbers, and the Ca²⁺ ion formed by losing both 4s electrons.

Z = 20 Ca Calcium

Calcium — Electron Configuration

Atomic number 20 · Alkaline earth metal · Period 4, Group 2 · s-block

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² [Ar] 4s² 20 electrons 2 valence e⁻

Subshell Breakdown

Subshell	Type	Electrons	Max Capacity	Notation
1s	s orbital, shell n=1	2	2	1s²
2s	s orbital, shell n=2	2	2	2s²
2p	p orbitals, shell n=2	6	6	2p⁶
3s	s orbital, shell n=3	2	2	3s²
3p	p orbitals, shell n=3	6	6	3p⁶
4s	s orbital, shell n=4 (valence)	2	2	4s²
Total		20

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

All subshells written explicitly (20 electrons total).

Noble-Gas Shorthand

[Ar] 4s²

[Ar] = 1s² 2s² 2p⁶ 3s² 3p⁶ (the 18-electron argon core).

Shell Fill Summary

Shell 1 (n=1) — 1s² 2 / 2 electrons (100%)

Shell 2 (n=2) — 2s² 2p⁶ 8 / 8 electrons (100%)

Shell 3 (n=3) — 3s² 3p⁶ 8 / 18 electrons (44%)

Shell 4 (n=4) — 4s² (valence) 2 / 32 electrons (6%)

Shell 3 can hold up to 18 electrons (3s + 3p + 3d), but calcium fills only the 3s and 3p subshells — 3d remains empty. Shell 4 contains only the two valence electrons in 4s.

Orbital Box Diagram

2 electrons (paired) — filled

6 electrons across 3 orbitals — filled

2 electrons (paired) — filled

6 electrons across 3 orbitals — filled

2 electrons (paired) — valence shell, lost to form Ca²⁺

Each box represents one orbital. Opposing arrows represent paired electrons with opposite spins (+½ and −½). Calcium is diamagnetic — all electrons are paired, leaving no net magnetic moment.

Quantum Numbers for All 20 Electrons

Electron #	n	l	mₗ	mₛ	Subshell
1	1	0	0	+½	1s
2	1	0	0	−½	1s
3	2	0	0	+½	2s
4	2	0	0	−½	2s
5	2	1	-1	+½	2p
6	2	1	-1	−½	2p
7	2	1	0	+½	2p
8	2	1	0	−½	2p
9	2	1	1	+½	2p
10	2	1	1	−½	2p
11	3	0	0	+½	3s
12	3	0	0	−½	3s
13	3	1	-1	+½	3p
14	3	1	-1	−½	3p
15	3	1	0	+½	3p
16	3	1	0	−½	3p
17	3	1	1	+½	3p
18	3	1	1	−½	3p
19 (valence)	4	0	0	+½	4s
20 (valence)	4	0	0	−½	4s

n = principal quantum number; l = azimuthal (l=0 → s, l=1 → p); mₗ = magnetic; mₛ = spin. Electrons 19–20 (highlighted) are the valence electrons removed when Ca becomes Ca²⁺.

Ca²⁺ Ion Formation

Neutral Atom

[Ar] 4s²

20 protons / 20 electrons

Loses 2 electrons

e⁻ e⁻

both 4s electrons removed

Ca²⁺

Ca²⁺ Ion

[Ar] = 1s² 2s² 2p⁶ 3s² 3p⁶

20 protons / 18 electrons

When calcium loses its two 4s valence electrons, the resulting Ca²⁺ ion is isoelectronic with argon — it has 18 electrons in the stable [Ar] noble-gas configuration. This filled-shell arrangement explains why calcium almost exclusively forms +2 compounds: a third ionization would require breaking into the stable argon core, requiring roughly 4,912 kJ/mol — far too high for typical chemistry.

Ca vs Ca²⁺ Comparison

Property	Ca (neutral)	Ca²⁺ (ion)
Electron count	20	18
Configuration	[Ar] 4s²	[Ar] (same as argon)
Valence electrons	2 (in 4s)	0 (4s empty)
Magnetic behavior	Diamagnetic	Diamagnetic
Ionic radius	197 pm (atomic)	100 pm (smaller — fewer e⁻)
Common role	Pure metal (reducing agent)	Mineral, biological ion

Ionization Energies

1st IE — removes 1st 4s electron 589.8 kJ/mol

2nd IE — removes 2nd 4s electron 1145.4 kJ/mol

3rd IE — would break [Ar] core (3p) 4,912.4 kJ/mol

The large jump from the 2nd to 3rd ionization energy (1145 → 4912 kJ/mol) confirms that calcium has exactly 2 valence electrons. Removing a 3rd electron would disrupt the stable argon core.

Summary