Magnesium
Atomic Data
| Atomic Number | 12 |
| Symbol | Mg |
| Atomic Weight | 24.305 u |
| Density (STP) | 1.738 g/cm³ |
| Melting Point | 649.85 °C (923 K) |
| Boiling Point | 1089.85 °C (1363 K) |
| Electronegativity | 1.31 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 |
| Oxidation States | +2 |
| Phase at STP | Solid |
| Category | Alkaline-Earth Metal |
| Period / Group | 3 / 2 |
| CAS Number | 7439-95-4 |
Electron Configuration
[Ne] 3s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| Total | 12 | 12 | ||
Isotopes of Magnesium
Magnesium has three naturally occurring stable isotopes. The most abundant is ²⁴Mg, comprising 78.99% of all naturally occurring Magnesium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Magnesium-24 | ²⁴Mg | 12 | 12 | 78.99 | Stable |
| Magnesium-25 | ²⁵Mg | 12 | 13 | 10.0 | Stable |
| Magnesium-26 | ²⁶Mg | 12 | 14 | 11.01 | Stable |
Abundance & Occurrence
Magnesium is present in Earth's crust at approximately 23300 ppm by mass and at approximately 6000 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Fire and flammability: Magnesium ribbon and powder ignite readily and burn with an intensely bright white flame reaching ~3100 °C; once ignited, magnesium is extremely difficult to extinguish.
- Water and CO2 incompatibility: Water and carbon dioxide extinguishers must never be used on magnesium fires — both react with burning magnesium, potentially causing explosions and spreading the fire; use dry sand or Class D extinguisher only.
- Dust explosion risk: Finely divided magnesium powder or swarf forms explosive mixtures with air; grinding and machining must be performed with ventilation and spark controls.
- Eye and skin hazard: Magnesium particles or the intense UV radiation from a magnesium flame can cause severe eye injury; use appropriate eye protection when handling or when any risk of ignition exists.
Magnesium in the Real World
Real-World Uses
- Lightweight structural alloys — Magnesium alloys (Mg-Al, Mg-Zn) are the lightest structural metals available, used in laptop and camera housings, car gearbox casings, steering wheels, and aircraft seat frames.
- Pyrotechnics and incendiaries — Magnesium metal burns with an intensely bright white flame (~3100 K), making it the active ingredient in military flares, signal rockets, incendiary munitions, and photographic flash powder.
- Dietary supplement and medicine — Magnesium is essential for over 300 enzyme reactions; magnesium sulfate (Epsom salt) is used to treat eclampsia, as a laxative, and in muscle-relaxing bath salts.
- Refractory materials — Magnesium oxide (periclase) withstands temperatures above 2800 °C and is used to line steel furnaces, cement kilns, and electrical resistance heating elements.
- Desulfurisation of steel and iron — Magnesium granules are injected into molten iron in ladle metallurgy to react with and remove sulfur, improving the quality and ductility of the final steel product.
- Chlorophyll and photosynthesis — Magnesium is the central atom of every chlorophyll molecule; plants, algae, and cyanobacteria depend on it to capture sunlight and drive photosynthetic carbon fixation.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is magnesium used for?
Magnesium is used in lightweight alloys for aerospace and automotive components, in incendiary flares and fireworks (it burns very brightly), in dietary supplements (essential for hundreds of enzyme reactions), in refractory materials for furnace linings, and in medical treatments such as magnesium sulfate (Epsom salt) for eclampsia and laxative use. It is also the central atom in chlorophyll, making it essential for photosynthesis.
Is magnesium a lightweight metal?
Yes, magnesium is the lightest structural metal in practical use, with a density of 1.74 g/cm³ — about two-thirds the weight of aluminium and a quarter of steel. Magnesium alloys offer an excellent strength-to-weight ratio, making them valuable where weight reduction is critical, such as in laptop and camera housings, car parts, aircraft seat frames, and aerospace structures.
Is magnesium good for your health?
Yes, magnesium is an essential mineral for human health. It is required for over 300 enzymatic reactions including those involved in energy production (ATP synthesis), protein synthesis, DNA replication, and nerve transmission. Magnesium deficiency (hypomagnesaemia) is relatively common and associated with muscle cramps, anxiety, sleep disturbances, and cardiovascular disease. Good dietary sources include nuts, seeds, legumes, whole grains, and dark green vegetables.
Why does magnesium burn so brightly?
Magnesium burns with an extraordinarily bright white light because it reacts very exothermically with both oxygen and nitrogen in air, producing magnesium oxide and magnesium nitride at temperatures around 3100°C. At this temperature, the white-hot magnesium oxide particles emit intense visible and ultraviolet light across a broad spectrum. The brightness is intense enough to cause temporary blindness — burning magnesium should never be looked at directly and cannot be extinguished with water or CO₂.