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 2p&sup6; 3s² |
| Oxidation States | +2 |
| Phase at STP | Solid |
| Category | Alkaline-earth metal |
| Period / Group | 3 / 2 |
| CAS Number | 7439-95-4 |
Electron Configuration
1s2 2s2 2p6 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, making up nearly 79% of all natural magnesium. All three isotopes are stable with no radioactive decay.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Magnesium-24 | ²⁴Mg | 12 | 12 | 78.99% | Stable |
| Magnesium-25 | ²⁵Mg | 12 | 13 | 10.00% | Stable |
| Magnesium-26 | ²⁶Mg | 12 | 14 | 11.01% | Stable |
Abundance & Occurrence
Magnesium is the eighth most abundant element in Earth's crust at approximately 23,300 ppm, and is the third most abundant element dissolved in seawater. In the universe it ranks seventh by mass abundance, formed primarily by carbon burning in massive stars. On Earth it occurs in important mineral deposits including dolomite, magnesite, and serpentine, and is extracted commercially from both ore and seawater.
EARTH'S CRUST COMPOSITION (BY MASS)
GLOBAL MAGNESIUM DEMAND BY SECTOR
Discovery & History
Safety & Handling
- Fire hazard — powder and ribbon: Finely divided magnesium powder and thin ribbon ignite easily and burn with an extremely intense white flame. Once ignited, magnesium is very difficult to extinguish.
- Do not use water on magnesium fires: Water reacts with burning magnesium to produce hydrogen gas, which can cause explosive flare-ups. Use dry sand, dry Class D extinguishers, or graphite powder instead.
- UV radiation hazard: Burning magnesium emits intense ultraviolet light that can cause permanent eye damage. Never look directly at burning magnesium without UV-rated eye protection.
- Bulk metal is generally safe: Solid ingots and castings are not readily flammable at room temperature and pose minimal hazard under normal handling. The fire risk increases dramatically with surface area (turnings, powder, ribbon).
- Magnesium compounds are generally non-toxic: Common compounds such as magnesium oxide, hydroxide, and sulfate are non-toxic and are widely used in food and medicine. Magnesium sulfate (Epsom salt) is used as a laxative and in therapeutic bath soaks.
- Storage: Store magnesium powder and ribbon in cool, dry conditions, away from oxidising agents, halogens, and moisture. Containers should be tightly sealed and clearly labelled as flammable solid.
Magnesium in the Real World
Real-World Uses
- Lightweight structural alloys — Magnesium is alloyed with aluminium to produce lightweight, high-strength materials used in aircraft fuselages, spacecraft, and automotive parts. Magnesium alloys are among the lightest structural metals, with density two-thirds that of aluminium.
- Pyrotechnics and flares — Magnesium powder and ribbon burn with intense white light, making them essential in military illumination flares, emergency signal flares, fireworks, and flash photography. Combustion temperatures can exceed 3000 °C.
- Antacid and laxative medicines — Magnesium hydroxide (milk of magnesia) neutralises stomach acid and relieves heartburn and indigestion. Magnesium sulfate (Epsom salt) acts as a saline laxative and is used intravenously to treat pre-eclampsia in pregnancy.
- Fertiliser additive — Magnesium is the central atom in the chlorophyll molecule and is essential for photosynthesis. Magnesium-deficient soils are treated with dolomitic limestone or magnesium sulfate to improve crop yields and plant health.
- Die-casting for electronics and automotive — Magnesium alloys are used in die-cast components for laptop housings, camera bodies, steering wheels, seat frames, and instrument panels, combining light weight with good dimensional stability and vibration damping.
- Steel desulfurisation — Magnesium metal is injected into molten steel to remove sulfur impurities, improving the toughness and weldability of the final product. This is one of the largest single industrial uses of magnesium worldwide.
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 engineering, as a component in pyrotechnics and military flares, in antacid and laxative medicines (as magnesium hydroxide), as a fertiliser additive to correct soil deficiencies, and in die-casting for electronics and car parts. It is also a critical mineral for human health, supporting muscle function and bone density.
Is magnesium a metal?
Yes. Magnesium is an alkaline-earth metal in Group 2, Period 3 of the periodic table. It is a shiny, silvery-white solid at room temperature with a density of 1.738 g/cm³ — making it one of the lightest structural metals available. It has a melting point of 649.85 °C and conducts both heat and electricity well.
Why does magnesium burn with a bright white flame?
When magnesium burns it reacts vigorously with oxygen in the air to form magnesium oxide (MgO). The reaction releases a large amount of energy, producing intense white light across the visible and ultraviolet spectrum. The temperature of burning magnesium can reach around 3100 °C, which is why it is used in flares, fireworks, and incendiary devices.
Is magnesium essential for human health?
Yes. Magnesium is an essential mineral for human health, involved in over 300 enzymatic reactions including energy production (ATP synthesis), DNA replication, protein synthesis, and muscle and nerve function. The human body contains approximately 25 g of magnesium, most of it stored in bones and muscles. Deficiency can cause muscle cramps, fatigue, and irregular heart rhythm.
Who discovered magnesium?
Magnesium as a distinct element was identified by Joseph Black in Edinburgh in 1755, who distinguished magnesia alba from calcium-containing compounds. Humphry Davy first isolated magnesium metal by electrolysis in 1808, and Antoine Bussy produced the first sizeable sample of pure magnesium metal in 1828 by reducing magnesium chloride with potassium.