---
title: "Magnesium (Mg): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/magnesium.html
description: "Magnesium (Mg), element 12: atomic mass 24.305, electron configuration [Ne] 3s², group 2, period 3, s-block alkaline earth metal. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
12Mg24.305

# Magnesium (Mg) – element 12

Magnesium is a chemical element with the symbol **Mg** and atomic number **12**. It is a alkaline earth metal in group 2 (alkaline earth metals), period 3 of the periodic table (s-block), and is a solid at room temperature.

Magnesium (Mg) has atomic number 12, atomic mass 24.305 u and electron configuration [Ne] 3s2.

[Download periodic table PDF](https://www.moldraw.com/printables/periodic-table.pdf)[Open interactive periodic table](https://www.moldraw.com/tools/free-chem-tools/interactive-periodic-table.html)

## Magnesium facts

| Symbol | Mg |
| --- | --- |
| Atomic number | 12 |
| Atomic mass | 24.305 u (g/mol) |
| Category | alkaline earth metal |
| Group | group 2 (alkaline earth metals) |
| Period | 3 |
| Block | s-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 |
| Noble-gas notation | [Ne] 3s2 |
| Electrons per shell | 2, 8, 2 |
| Valence electrons | 2 |

## Bohr model and shells

Magnesium has 12 electrons in 3 shells: 2, 8, 2. Full configuration and noble-gas notation are in the table; work out any element or ion with the [electron configuration calculator](https://www.moldraw.com/tools/free-chem-tools/electron-configuration-calculator.html).

## Physical and atomic properties

| Melting point | 923 K (649.9 °C) |
| --- | --- |
| Boiling point | 1363 K (1089.8 °C) |
| Density | 1.738 g/cm³ |
| Electronegativity (Pauling) | 1.31 |
| Electron affinity | -40 kJ/mol |
| Ionization energies | 737.7, 1450.7, 7732.7 kJ/mol (1st, 2nd, 3rd) |
| Molar heat capacity | 24.869 J/(mol·K) |
| Discovered by | Joseph Black |

Use the atomic mass in the [molar mass calculator](https://www.moldraw.com/tools/free-chem-tools/molar-mass-calculator.html) for any formula containing Mg.

## Position in the periodic table

Tap any element to open its page.

## Frequently asked questions

### What is the atomic mass of magnesium?

The atomic mass of magnesium is 24.305 u, so one mole of magnesium atoms weighs 24.305 g.

### What is the electron configuration of magnesium?

Magnesium has 12 electrons: 1s² 2s² 2p⁶ 3s², or [Ne] 3s² in noble-gas notation. Electrons per shell: 2, 8, 2.

### How many valence electrons does magnesium have?

Magnesium has 2 valence electrons (group 2).

### Is magnesium a metal?

Yes. Magnesium is a alkaline earth metal.

### Where is magnesium on the periodic table?

Magnesium is in group 2 (alkaline earth metals), period 3, in the s-block.

Data: [Periodic-Table-JSON](https://github.com/Bowserinator/Periodic-Table-JSON) (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.