---
title: "Magnesium (Mg) — element 12"
description: "Magnesium is element 12, symbol Mg, atomic weight 24.305. Configuration, properties, uses and neighbours."
url: https://atoneplace.net/element/magnesium/
site: "At One Place"
---

# Magnesium (Mg)

**Magnesium — element 12: Mg**

24.305 u · Alkaline earth metal · period 3, group 2

Magnesium is the lightest structural metal in ordinary use, about a third lighter than aluminium, and it is the fourth most abundant element in the Earth as a whole. A magnesium atom sits at the centre of every chlorophyll molecule, so the colour of every leaf on the planet depends on it. Burning magnesium reaches around 3,100 °C and keeps burning inside carbon dioxide or steam, which is why a magnesium fire in a machine shop cannot be fought with an ordinary extinguisher.

## Properties

- **Atomic number:** 12
- **Symbol:** Mg
- **Standard atomic weight:** 24.305 u
- **Category:** Alkaline earth metal
- **Group:** 2
- **Period:** 3
- **Block:** s-block
- **Electron configuration:** [Ne] 3s²
- **Electrons per shell:** 2, 8, 2
- **Melting point:** 923 K — 649.9 °C — 1201.7 °F
- **Boiling point:** 1,363 K — 1089.8 °C — 1993.7 °F
- **Density:** 1.74 g/cm³
- **Electronegativity:** 1.31 (Pauling)
- **Oxidation states:** +2
- **Discovered:** 1808 by Humphry Davy

## Electron configuration

- **Full:** 1s² 2s² 2p⁶ 3s²
- **Noble gas shorthand:** [Ne] 3s²
- **Shells:** K: 2 · L: 8 · M: 2

## What it is used for

- Lightweight alloy castings for gearboxes, laptops and camera bodies
- Sacrificial anodes in water heaters and buried steel pipelines
- Epsom salts and milk of magnesia
- Magnesium chloride for de-icing roads
- Flares, fireworks and emergency fire-starters

## Hazards

- Burning magnesium cannot be extinguished with water, foam or carbon dioxide
- The flame emits enough ultraviolet to damage eyes at close range
- Fine swarf and dust are an explosion hazard in machine shops

> IUPAC publishes an interval, [24.304, 24.307]; 24.305 is the conventional value.

## Neighbours in the table

| Z | Element | Symbol | Mass |
| --- | --- | --- | --- |
| 10 | Neon | Ne | 20.18 |
| 11 | Sodium | Na | 22.99 |
| 12 | Magnesium ← | Mg | 24.305 |
| 13 | Aluminum | Al | 26.982 |
| 14 | Silicon | Si | 28.085 |

## Group 2

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Magnesium sits in group 2 with beryllium, calcium, strontium, barium, radium.

## Common questions

### What is the atomic number of magnesium?

12. That is the number of protons in its nucleus, which is what defines the element.

### What is the symbol for magnesium?

Mg.

### What is the electron configuration of magnesium?

1s² 2s² 2p⁶ 3s², or [Ne] 3s² in noble-gas shorthand.

### What is the melting point of magnesium?

923 K — 649.9 °C — 1201.7 °F

## Related pages

- [Neon (Ne)](https://atoneplace.net/element/neon/)
- [Sodium (Na)](https://atoneplace.net/element/sodium/)
- [Aluminum (Al)](https://atoneplace.net/element/aluminum/)
- [Silicon (Si)](https://atoneplace.net/element/silicon/)
- [Beryllium (Be)](https://atoneplace.net/element/beryllium/)
- [Calcium (Ca)](https://atoneplace.net/element/calcium/)
- [Strontium (Sr)](https://atoneplace.net/element/strontium/)
- [Barium (Ba)](https://atoneplace.net/element/barium/)
- [Radium (Ra)](https://atoneplace.net/element/radium/)

## Sources

- Official vendor product documentation — At One Place (/about/)