Atomic number 12 · Alkaline earth metal
Magnesium Mg
Magnesium is a light, silvery alkaline earth metal and the lightest metal widely used in structural parts. It sits at the centre of every chlorophyll molecule, making it essential for photosynthesis, and it is a vital mineral for hundreds of enzymes in the human body.
Key properties
| Atomic number | 12 |
|---|---|
| Atomic weight | 24.305 (CIAAW 2024 abridged standard atomic weight) |
| Category | Alkaline earth metal |
| Group | 2 |
| Period | 3 |
| Block | s |
| State (25 °C, 1 atm) | Solid |
| Melting point | 923 K (649.9 °C) |
| Boiling point | 1363 K (1089.8 °C) |
| Density | 1.74 g/cm³ |
| Electronegativity (Pauling) | 1.31 |
| Atomic radius (van der Waals) | 173 pm |
| First ionization energy | 7.646 eV |
| Electron affinity | — |
| Oxidation states | +2 |
| Discovered | 1808 |
Electron configuration
- Condensed
- [Ne]3s2
- Full
- 1s2 2s2 2p6 3s2
- Electrons per shell
- 2 · 8 · 2
Orbital diagram
Position in the table
Discovery
In 1618, according to tradition, a farmer at Epsom in England noticed that his cattle would not drink from a bitter spring. The water turned out to contain magnesium sulfate, which became famous as Epsom salt, a remedy for many ailments.
In 1755 the Scottish chemist Joseph Black showed that magnesia (magnesium oxide and carbonate) was a distinct substance from lime (calcium compounds), an important step in recognising magnesium as separate. Humphry Davy obtained an impure amalgam of the metal by electrolysis in 1808, and the French chemist Antoine Bussy produced a coherent sample around 1831 by reducing magnesium chloride with potassium. Robert Bunsen later developed the electrolysis of molten magnesium chloride, the forerunner of modern production methods.
Origin of the name
The name comes from Magnesia, a district of Thessaly in Greece, where minerals such as magnesia alba were found. The same place-name gave rise to the words magnet and manganese, which caused much confusion among early chemists. The symbol is Mg.
Main uses
- Lightweight alloys: magnesium alloys are used in car steering wheels, gearbox housings, laptop and camera bodies, and power tools.
- Aluminium alloys: small additions of magnesium strengthen the aluminium in drink cans and many structural parts.
- Metallurgy: magnesium removes sulfur from molten iron and reduces titanium tetrachloride to titanium metal in the Kroll process.
- Pyrotechnics: burning magnesium gives an intense white light used in flares and fireworks.
- Medicine and industry: magnesium hydroxide is an antacid and laxative, and heat-resistant magnesium oxide lines furnaces.
Isotopes
Magnesium has three stable isotopes: magnesium-24 (about 79 percent), magnesium-25 (about 10 percent) and magnesium-26 (about 11 percent). Some meteorite minerals contain extra magnesium-26 formed by the decay of the short-lived isotope aluminium-26, allowing scientists to measure the timing of events in the first few million years of the solar system. Magnesium-25 is useful in NMR and biological tracer studies. Its radioactive isotopes are short-lived.
In everyday life
An adult body contains roughly 25 grams of magnesium, mostly in bones, and it is needed by more than 300 enzymes, including those that handle energy and build DNA. Leafy greens, nuts, seeds and whole grains are good sources; green vegetables are green because of magnesium-containing chlorophyll.
Magnesium ribbon and shavings burn fiercely once ignited, and water can make a magnesium fire worse, so special extinguishers are used.
Good to know
- With a density of about 1.74 g/cm³, magnesium is roughly two thirds as dense as aluminium.
- Early photographers used burning magnesium powder as a flash.
- Magnesium is abundant in seawater, from which it is commercially extracted in some plants.
Same group (2)
Data sources · Properties: PubChem Periodic Table (US NIH/NLM public data) · Atomic weights: CIAAW 2024 abridged standard atomic weights · Names: Wikidata (CC0); Korean names follow the Korean Chemical Society. Retrieved 2026-09-23.