Magnesium
Magnesium is a chemical element with symbol Mg and atomic number 12. It is a shiny gray solid which bears a close physical resemblance to the other five elements in the second column (Group 2, or alkaline earth metals) of the periodic table:they each have the same electron configuration in their outer electron shell producing a similar crystal structure. Magnesium is the ninth most abundant element in the universe.
Identity
- Atomic mass
- [24.304, 24.307] u
- Category
- Alkaline earth metals
- Group
- 2
- Period
- 3
- Block
- s
- Oxidation States
- +2
- Phase (25 °C)
- Solid
- Appearance
- shiny grey solid
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2
- Short configuration
- [Ne] 3s2
- Electrons per shell
- 2, 8, 2
- Electronegativity (Pauling)
- 1.31
- Electron affinity
- -40 kJ/mol
- 1st ionization energy
- 738 kJ/mol
- Ionization energies
- 738 · 1451 · 7733 · 10543 · 13630… kJ/mol
Physical properties
- Melting point
- 649.9 °C (923 K)
- Boiling point
- 1089.8 °C (1363 K)
- Density
- 1.738 g/cm³
- Molar heat capacity
- 24.9 J/(mol·K)
Chemical behavior of magnesium
Magnesium has two valence electrons ([Ne] 3s2) that it readily cedes to keep neon's octet: it acts almost always as +2 in ionic or polar bonds, with low electronegativity (1.31). It is less reactive than alkali metals because its second ionization energy is higher and it is shielded by an oxide layer, but once started it burns with a blinding flame. Its small, strongly hydrated cation (Mg2+) is the one in chlorophyll and hundreds of enzymes.
Reactivity
2 Mg + O₂ → 2 MgO
It burns in air with a blinding white flame (about 3,100 C) giving magnesium oxide. The light is so intense it was used in photographic flashes and flares; looking at it harms eyesight.
Mg + 2 H₂O → Mg(OH)₂ + H₂
With cold water it reacts slowly because of its protective oxide layer, but with steam or hot water it gives hydroxide and releases hydrogen. Water does not put out a magnesium fire: it feeds it.
3 Mg + N₂ → Mg₃N₂
Heated in nitrogen it forms magnesium nitride, which few metals achieve given the strength of N triple N. With water, the nitride releases ammonia.
2 Mg + CO₂ → 2 MgO + C
It burns even in carbon dioxide, stealing its oxygen and leaving carbon. So CO2 extinguishers are banned on magnesium fires: only dry sand or special powder work.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Magnesium oxide | MgO | Furnace refractories, antacids and cement |
| Magnesium sulfate | MgSO₄ | Epsom salts, fertilizers and medicine |
| Magnesium hydroxide | Mg(OH)₂ | Antacid (milk of magnesia) and flame retardant |
| Magnesium carbonate | MgCO₃ | Magnesite, sport chalk and fireproof materials |
| Chlorophyll a | C₅₅H₇₂MgN₄O₅ | Photosynthesis pigment in all plants |
Electron shell distribution
View in the atom builderIsotopes
Natural magnesium combines three stable isotopes: magnesium-24 (24Mg, about 79%), magnesium-25 (about 10%) and magnesium-26 (about 11%), all with twelve protons. 26Mg, daughter of extinct aluminium-26, dates the formation of the Solar System's first solids in meteorites.
Occurrence and production
It is the eighth crust element (about 2.3%) and the third dissolved in the sea (1,300 ppm). It appears in dolomite, magnesite, olivine and carnallite, and as Mg2+ in seawater. It is obtained by electrolysis of molten chloride or by thermal reduction (Pidgeon process), and increasingly from seawater.
History and origin of the name
Joseph Black distinguished magnesia from lime in 1755, and Humphry Davy isolated the metal by electrolysis in 1808. It takes its name from Magnesia, the Greek region rich in magnesite. Its blinding flame made it a star of 19th-century photography and of incendiary bombs in the world wars.
Applications and relevance of magnesium
Uses of the element
Alloyed with aluminium it forms ultralight metals for wheels, laptop cases, bicycles and aircraft parts. It burns in flares, flashes and pyrotechnics, and deoxidizes steel and titanium in metallurgy.
Uses of its compounds
Milk of magnesia relieves acidity; Epsom salts relax muscles and fertilize fields; magnesite lines furnaces; chlorophyll magnesium captures sunlight.
Health, safety and environment
Biological role
It is essential: chlorophyll centers it, and hundreds of enzymes and muscles need Mg2+. Nuts, legumes and greens supply it; deficiency brings cramps.
Safety
Solid metal is safe, but powder and machining chips ignite easily and burn at extreme heat; water and CO2 feed the fire. Only dry sand or class D powder work.
Environment
Abundant and recyclable, with low toxicity. Electrolysis production consumes much energy, but light alloys save fuel in transport.
Frequently asked questions about Magnesium
Why does magnesium burn with such blinding light?
Because its combustion releases huge energy at about 3,100 C, and at that temperature glowing oxide emits intense white light rich in ultraviolet. Before the electric flash, photographers burned magnesium ribbon for portraits. Looking straight at it can injure the retina.
What has magnesium to do with plants?
Everything: every chlorophyll molecule carries one magnesium atom at its center, capturing sunlight for photosynthesis. Without soil magnesium, leaves yellow and the plant starves. Fertilizers include it as a secondary nutrient. Every green bite owes something to Mg2+.
Why do wheels and laptops use magnesium?
Because its alloys are the lightest structural ones: 35% lighter than aluminium with comparable strength. Less weight means less consumption in cars and planes, and laptops that do not break backs. The trick is alloying it with aluminium or zinc, which curb corrosion.
Could seawater give us endless magnesium?
Almost: each litre of sea holds 1.3 grams of magnesium, and plants already extract it by precipitating hydroxide with lime. The obstacle is energy and cost, not geology: today mining dolomite is cheaper. If energy gets cheaper, the sea will be the magnesium mine of the future.
Why must a magnesium fire not be put out with water?
Because red-hot magnesium splits water into hydrogen, which burns in turn, and CO2 into carbon and oxygen feeding the flame: pouring water is like pouring petrol. Only dry sand, which smothers it, or special class D powders work.
Do magnesium supplements help cramps?
Only with deficiency: magnesium regulates muscle contraction and lack raises cramps, common in athletes. But with normal levels extra gives no more performance and excess causes diarrhoea. Bananas, nuts, legumes and whole grains usually suffice.
What are Epsom salts?
Hydrated magnesium sulfate, found at Epsom springs in England: a bitter powder used since the 17th century as a purgative, muscle relaxant in hot baths and fertilizer. In medicine it is injected against preeclampsia and arrhythmias. A classic remedy modern chemistry confirmed.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.