What is the electron configuration of magnesium?

Magnesium (Mg, Z=12) has the ground-state electron configuration 1s² 2s² 2p⁶ 3s². Its 12 electrons fill the first two shells completely, with 2 valence electrons in the 3s subshell.

What is the noble-gas shorthand for magnesium?

The condensed (noble-gas) notation is [Ne] 3s², where [Ne] represents the filled 1s² 2s² 2p⁶ core shared with neon (atomic number 10).

Why does magnesium form a +2 ion?

Magnesium loses both 3s² valence electrons to achieve the stable [Ne] (1s² 2s² 2p⁶) noble-gas core, resulting in the Mg²⁺ ion.

How many valence electrons does magnesium have?

Magnesium has 2 valence electrons, both located in the 3s subshell. This is why it is in Group 2 of the periodic table.

What block and period is magnesium in?

Magnesium is in Period 3, Group 2 (the alkaline earth metals), and belongs to the s-block of the periodic table because its outermost electrons are in an s subshell.

How does magnesium's configuration differ from sodium?

Sodium (Na, Z=11) is 1s² 2s² 2p⁶ 3s¹ — one electron in 3s. Magnesium adds one more electron to complete the 3s subshell: 1s² 2s² 2p⁶ 3s². Both are Period 3 elements.

What is the 2p subshell in magnesium?

The 2p subshell contains 3 orbitals, each holding 2 electrons, for a total of 6 electrons (2p⁶). This subshell is fully filled in magnesium, making it part of the [Ne] core.

Magnesium Electron Configuration

Name: Magnesium Electron Configuration
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Author: Nham Vu

Interactive reference for magnesium's electron configuration (1s² 2s² 2p⁶ 3s²), orbital diagram, shell fill, and key atomic properties.

Z = 12 Mg Magnesium

Magnesium — Electron Configuration

Atomic number 12 · Alkaline earth metal · Period 3, Group 2 · s-block

1s² 2s² 2p⁶ 3s² [Ne] 3s² 12 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 (×3), shell n=2	6	6	2p⁶
3s	s orbital, shell n=3 (valence)	2	2	3s²
Total		12

Full Configuration

1s² 2s² 2p⁶ 3s²

All subshells written explicitly in Aufbau order.

Noble-Gas Shorthand

[Ne] 3s²

[Ne] = 1s² 2s² 2p⁶ (the filled neon core, 10 electrons).

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 only (valence) 2 / 18 electrons (11%)

Shell 3 can hold up to 18 electrons (3s + 3p + 3d). Magnesium uses only the 3s subshell, leaving 3p and 3d empty.

Orbital Box Diagram

2 electrons (paired) — filled

mₗ=−1

mₗ=0

mₗ=+1

6 electrons (3 pairs) — filled

2 valence electrons (paired) — outermost shell

Each box represents one orbital. Opposing arrows represent paired electrons with opposite spins (+½ and −½), satisfying the Pauli exclusion principle. The highlighted 3s orbital is the valence shell.

Quantum Numbers for All 12 Electrons

e⁻ #	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

Summary

Interactive reference for magnesium's electron configuration (1s² 2s² 2p⁶ 3s²), orbital diagram, shell fill, and key atomic properties.

How it works

The Aufbau principle fills subshells from lowest to highest energy: 1s, 2s, 2p, then 3s.
Magnesium's 12 electrons fill three complete subshells (1s², 2s², 2p⁶) and one valence subshell (3s²).
The orbital box diagram represents each orbital as a box; paired arrows show electrons with opposite spins (Pauli exclusion principle).
Noble-gas notation replaces the inner filled core with the nearest noble gas in brackets: [Ne] 3s².
The three interactive tabs let you explore the configuration, orbital diagram, and element data separately.

Use cases

Quick reference for chemistry homework or exam review on electron configuration.
Visualize how the Aufbau principle fills the 1s, 2s, 2p, and 3s subshells.
Understand why magnesium forms a +2 ion by losing both 3s valence electrons.
Compare magnesium to other alkaline earth metals such as beryllium and calcium.
Learn noble-gas shorthand notation using [Ne] 3s² as a clear example.
Teaching aid for introductory atomic structure and periodic table lessons.
Reference quantum numbers for each of magnesium's 12 electrons.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu