Magnesium
Magnesium is a lightweight, silvery alkaline earth metal known for burning with an intensely bright white flame and for sitting at the center of every chlorophyll molecule, making it essential to photosynthesis. It's also one of the most useful lightweight structural metals, widely alloyed with aluminum for parts where reducing weight matters.
- Group · Period
- 2 · 3
- At room temp
- solid
- Melts at
- 923 K
- Density
- 1.74 g/cm³
- Discovered
- 1808
Uses
Magnesium’s biggest structural role is in lightweight alloys, most often combined with aluminum, to make parts for cars, aircraft, and portable electronics housings where every gram of weight saved matters. Its bright, intense burn also makes it useful in flares, fireworks, and other pyrotechnic applications, a property first exploited in early photographic flashbulbs.
Magnesium compounds have their own wide range of uses: magnesium oxide is used in refractory materials that line furnaces because it withstands extreme heat, and magnesium hydroxide is the active ingredient in some antacids and laxatives. Magnesium is also a nutritionally essential mineral, required by the body for muscle and nerve function and involved in hundreds of enzyme reactions.
History
Magnesium was identified as a distinct element in 1808 by English chemist Humphry Davy, who used electrolysis to isolate it after earlier chemists had already recognized that magnesia — a mineral long confused with lime — was actually a different substance. Its name comes from the Magnesia region of Greece, an area associated with magnesium-bearing minerals found there long before the element itself was understood.
Fun facts
- Magnesium sits at the center of the chlorophyll molecule, the pigment that lets plants capture sunlight and carry out photosynthesis.
- It burns with such an intensely bright white light that it was used in early photography flashbulbs and is still used in flares and fireworks today.
- As one of the lightest structural metals available, magnesium is commonly alloyed with aluminum to make parts stronger without adding much weight.
Frequently asked questions
Why is magnesium so hard to put out once it catches fire?
Burning magnesium reacts so vigorously with oxygen that it releases enormous heat and light, and it can even react with nitrogen and carbon dioxide, meaning ordinary fire extinguishers or even water often can't smother it. Specialized dry powder extinguishers are needed for magnesium fires precisely because common suppression methods can make it worse.
Is magnesium metal the same thing as the magnesium in supplements?
No. Dietary supplements use stable magnesium compounds, such as magnesium citrate or magnesium oxide, which dissolve safely in the body and provide magnesium ions needed for muscle function, nerve signaling, and hundreds of enzyme reactions. Reactive magnesium metal is nothing like the compounds found in a supplement bottle.
Why is magnesium used in cars and aircraft?
It's one of the lightest metals with useful structural strength, especially when alloyed with aluminum or other metals. Reducing weight in vehicles and aircraft improves fuel efficiency and performance, making magnesium alloys attractive for wheels, frames, and other components despite being more expensive than steel.
Compounds
4 notable compounds containing Mg
- MgCl2salt
Magnesium chloride
A highly soluble ionic salt that readily absorbs moisture from air, and one of the major dissolved salts extracted from seawater.
Used for: Road de-icing, tofu coagulant (nigari), magnesium metal production
- Mg(OH)2base
Magnesium hydroxide
A weak, poorly soluble base that forms a milky suspension in water, giving rise to its common name.
Used for: Antacid and laxative (milk of magnesia), flame retardant filler
- MgOoxide
Magnesium oxide
An ionic oxide with a very high melting point, known in its mineral form as magnesia.
Used for: Refractory furnace linings, antacid and laxative, dietary supplement
- MgSO4salt
Magnesium sulfate
An ionic salt best known in its hydrated form, Epsom salt, which dissolves readily in water to give a bitter-tasting solution.
Used for: Epsom salt baths, soil magnesium supplement, medical treatment
Isotopes
23 known isotopes
Swipe to see all columns →
| Isotope | Natural abundance | Half-life | Decay mode | Mass excess | Binding energy / nucleon | Decay width |
|---|---|---|---|---|---|---|
| Mg-24 stable | 78.965% | Stable | — | -13,933.58 keV | 8,260.71 keV | — |
| Mg-25 stable | 10.011% | Stable | — | -13,192.78 keV | 8,223.5 keV | — |
| Mg-26 stable | 11.025% | Stable | — | -16,214.54 keV | 8,333.87 keV | — |
Show all 23 isotopes
| Mg-18 | — | 0.12 MeV | Two-proton emission (100%) | — | — | 1.20 × 105 eV |
| Mg-19 | — | 1.14E-4 eV | Two-proton emission (100%) | 31,838.39 keV | 5,901.5 keV | 1.14 × 10-4 eV |
| Mg-20 | — | 90.4 ms | Beta-plus decay (100%), Beta-plus, proton emission (30.3%) | 17,477.69 keV | 6,728.03 keV | 5.05 × 10-15 eV |
| Mg-21 | — | 122 ms | Electron capture / beta-plus decay (100%), Beta-plus, proton emission (32.6%), Beta-plus, alpha emission (0.5%) | 10,903.85 keV | 7,105.03 keV | 3.74 × 10-15 eV |
| Mg-22 | — | 3.8755 s | Electron capture / beta-plus decay (100%) | -399.99 keV | 7,662.76 keV | 1.18 × 10-16 eV |
| Mg-23 | — | 11.3046 s | Electron capture / beta-plus decay (100%) | -5,473.68 keV | 7,901.12 keV | 4.04 × 10-17 eV |
| Mg-27 | — | 9.458 m | Beta-minus decay (100%) | -14,586.59 keV | 8,263.85 keV | 8.04 × 10-19 eV |
| Mg-28 | — | 20.915 h | Beta-minus decay (100%) | -15,019.95 keV | 8,272.45 keV | 6.06 × 10-21 eV |
| Mg-29 | — | 1.30 s | Beta-minus decay (100%) | -10,612.36 keV | 8,113.53 keV | 3.51 × 10-16 eV |
| Mg-30 | — | 335 ms | Beta-minus decay (100%) | -8,881.37 keV | 8,054.43 keV | 1.36 × 10-15 eV |
| Mg-31 | — | 270 ms | Beta-minus decay (100%), Beta-minus, neutron emission (6.2%) | -3,122.15 keV | 7,869.19 keV | 1.69 × 10-15 eV |
| Mg-32 | — | 86 ms | Beta-minus decay (100%), Beta-minus, neutron emission (5.5%) | -828.9 keV | 7,803.84 keV | 5.31 × 10-15 eV |
| Mg-33 | — | 90.5 ms | Beta-minus decay (100%), Beta-minus, neutron emission (14%) | 4,962.87 keV | 7,636.44 keV | 5.04 × 10-15 eV |
| Mg-34 | — | 20 ms | Beta-minus decay (100%), Beta-minus, neutron emission | 8,323.32 keV | 7,550.39 keV | 2.28 × 10-14 eV |
| Mg-35 | — | 11.3 ms | Beta-minus decay (100%), Beta-minus, neutron emission (52%), B-3N | 15,639.79 keV | 7,356.23 keV | 4.04 × 10-14 eV |
| Mg-36 | — | 7.6 ms | Beta-minus decay (100%), Beta-minus, neutron emission | 20,380.16 keV | 7,244.42 keV | 6.00 × 10-14 eV |
| Mg-37 | — | 8 ms | Neutron emission, Beta-minus, neutron emission, Beta-minus decay | 28,211.48 keV | 7,055.11 keV | 5.70 × 10-14 eV |
| Mg-38 | — | — | Beta-minus decay (100%), Beta-minus, neutron emission, B-2N | 34,074 keV | 6,928 keV | — |
| Mg-39 | — | 180 ns | Neutron emission | 42,775 keV | 6,734 keV | 2.53 × 10-9 eV |
| Mg-40 | — | — | Beta-minus decay (100%), B-7N, B-6N | 49,550 keV | 6,598 keV | — |