Magnesium
[Ne] 3s² · 2 · 8 · 2
A light structural metal and the central atom of chlorophyll. Magnesium is nearly a quarter lighter than aluminium, burns with a blinding white flame, and sits inside every green leaf on the planet.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 12
- Atomic mass
- 24.305 а.е.м.
- Electron configuration
- [Ne] 3s²
- Electrons per shell
- 2 · 8 · 2
- Block
- s-block
- Group
- Alkaline earth metals
- Period
- 3
- Electronegativity (Pauling)
- 1.31
- Electronegativity (Allen)
- 1.29
- Atomic radius
- 145 pm
- Covalent radius
- 141 pm
- Van der Waals radius
- 173 pm
- Ionisation energy 1
- 737.7 kJ/mol
- Ionisation energy 2
- 1 450.7 kJ/mol
- Ionisation energy 3
- 7 732.7 kJ/mol
- Electron affinity
- 0 kJ/mol
- Common oxidation states
- +2
- Oxidation states
- +1, +2
Physical properties
- State at 25 °C
- solid
- Density
- 1.738 g/cm³
- Melting point
- 923 K · 649.9 °C
- Boiling point
- 1 363 K · 1 089.9 °C
- Speed of sound
- 4 940 m/s
Thermal properties
- Heat of fusion
- 8.48 kJ/mol
- Heat of vaporisation
- 128 kJ/mol
- Specific heat capacity
- 1.023 J/(g·K)
- Thermal conductivity
- 156 W/(m·K)
Mechanical properties
- Young's modulus
- 45 GPa
- Shear modulus
- 17 GPa
- Bulk modulus
- 45 GPa
- Poisson ratio
- 0.29
- Mohs hardness
- 2.5
- Brinell hardness
- 260 MPa
Electrical and magnetic properties
- Electrical resistivity
- 43.9 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- hexagonal close-packed (hcp)
- Lattice constants
- a = 320.94 pm · c = 521.05 pm
Abundance
- In the crust
- 23 300 mg/kg
- In the ocean
- 1 290 mg/L
- In the universe
- 600 000 mg/kg
- In the human body
- 270 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 24Mg | 78.99 % | stable | — |
| 25Mg | 10 % | stable | — |
| 26Mg | 11.01 % | stable | — |
Magnesium-26 in meteorites is the decay product of aluminium-26, and its excess dates the first solids of the Solar System.
Discovery
- Year of discovery
- 1755
- Discovered by
- Joseph Black
- Where
- Scotland
- Origin of the name
- from Magnesia, a district in Thessaly, source of magnesite
History
Joseph Black showed in 1755 that magnesia and lime were different substances. Davy isolated the metal in 1808; industrial production started a century later.
Where it occurs
The eighth most abundant element in the crust at 23 300 mg/kg, and the second most abundant cation in seawater. The main minerals are dolomite, magnesite and carnallite.
How it is produced
By electrolysing molten magnesium chloride recovered from seawater or brine, or by the silicothermic Pidgeon process from dolomite.
Role in living things
Magnesium is a cofactor for over three hundred enzymes, including every one that handles ATP. In chlorophyll it is the magnesium ion that holds the porphyrin ring and starts photosynthesis.
Safety
Burning magnesium is bright enough to damage the retina, and water must never be used on it — that releases hydrogen. Magnesium salts are of low toxicity; excess acts as a laxative.
Uses
- Alloys for automotive and aerospace parts — the lightest structural metal
- Reducing agent in the Kroll process for titanium
- Sacrificial anodes protecting steel structures from corrosion
- Pyrotechnics and illumination flares
- Magnesium oxide as a refractory and as an antacid
Curiosities
- Without magnesium there would be no photosynthesis: it is the centre of the chlorophyll molecule.
- Burning magnesium keeps burning in carbon dioxide, and even in sand.
- Epsom salts are magnesium sulfate.
- Magnesium is six times lighter than steel at comparable specific strength.