Magnesium | ||||||||||||||||||||||||||
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Pronunciation | /mæɡˈniːziəm/ | |||||||||||||||||||||||||
Appearance | shiny grey solid | |||||||||||||||||||||||||
Standard atomic weight Ar°(Mg) | ||||||||||||||||||||||||||
Magnesium in the periodic table | ||||||||||||||||||||||||||
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Atomic number (Z) | 12 | |||||||||||||||||||||||||
Group | group 2 (alkaline earth metals) | |||||||||||||||||||||||||
Period | period 3 | |||||||||||||||||||||||||
Block | s-block | |||||||||||||||||||||||||
Electron configuration | [Ne] 3s2 | |||||||||||||||||||||||||
Electrons per shell | 2, 8, 2 | |||||||||||||||||||||||||
Physical properties | ||||||||||||||||||||||||||
Phase at STP | solid | |||||||||||||||||||||||||
Melting point | 923 K (650 °C, 1202 °F) | |||||||||||||||||||||||||
Boiling point | 1363 K (1091 °C, 1994 °F) | |||||||||||||||||||||||||
Density (at 20° C) | 1.737 g/cm3[3] | |||||||||||||||||||||||||
when liquid (at m.p.) | 1.584 g/cm3 | |||||||||||||||||||||||||
Heat of fusion | 8.48 kJ/mol | |||||||||||||||||||||||||
Heat of vaporization | 128 kJ/mol | |||||||||||||||||||||||||
Molar heat capacity | 24.869[4] J/(mol·K) | |||||||||||||||||||||||||
Vapor pressure
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Atomic properties | ||||||||||||||||||||||||||
Oxidation states | common: +2 0,[5] +1[6] | |||||||||||||||||||||||||
Electronegativity | Pauling scale: 1.31 | |||||||||||||||||||||||||
Ionization energies |
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Atomic radius | empirical: 160 pm | |||||||||||||||||||||||||
Covalent radius | 141±7 pm | |||||||||||||||||||||||||
Van der Waals radius | 173 pm | |||||||||||||||||||||||||
Spectral lines of magnesium | ||||||||||||||||||||||||||
Other properties | ||||||||||||||||||||||||||
Natural occurrence | primordial | |||||||||||||||||||||||||
Crystal structure | hexagonal close-packed (hcp) (hP2) | |||||||||||||||||||||||||
Lattice constants | a = 320.91 pm c = 521.03 pm (at 20 °C)[3] | |||||||||||||||||||||||||
Thermal expansion | 25.91×10−6/K (at 20 °C)[3][a] | |||||||||||||||||||||||||
Thermal conductivity | 156[7] W/(m⋅K) | |||||||||||||||||||||||||
Electrical resistivity | 43.9[8] nΩ⋅m (at 20 °C) | |||||||||||||||||||||||||
Magnetic ordering | paramagnetic | |||||||||||||||||||||||||
Molar magnetic susceptibility | +13.1×10−6 cm3/mol (298 K)[9] | |||||||||||||||||||||||||
Young's modulus | 45 GPa | |||||||||||||||||||||||||
Shear modulus | 17 GPa | |||||||||||||||||||||||||
Bulk modulus | 35.4[10] GPa | |||||||||||||||||||||||||
Speed of sound thin rod | 4940 m/s (at r.t.) (annealed) | |||||||||||||||||||||||||
Poisson ratio | 0.290 | |||||||||||||||||||||||||
Mohs hardness | 1–2.5 | |||||||||||||||||||||||||
Brinell hardness | 44–260 MPa | |||||||||||||||||||||||||
CAS Number | 7439-95-4 | |||||||||||||||||||||||||
History | ||||||||||||||||||||||||||
Naming | after Magnesia, Greece[11] | |||||||||||||||||||||||||
Discovery | Joseph Black (1755[11]) | |||||||||||||||||||||||||
First isolation | Humphry Davy (1808[11]) | |||||||||||||||||||||||||
Isotopes of magnesium | ||||||||||||||||||||||||||
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Magnesium is a chemical element; it has symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic table) it occurs naturally only in combination with other elements and it almost always has an oxidation state of +2. It reacts readily with air to form a thin passivation coating of magnesium oxide that inhibits further corrosion of the metal. The free metal burns with a brilliant-white light. The metal is obtained mainly by electrolysis of magnesium salts obtained from brine. It is less dense than aluminium and is used primarily as a component in strong and lightweight alloys that contain aluminium.
In the cosmos, magnesium is produced in large, aging stars by the sequential addition of three helium nuclei to a carbon nucleus. When such stars explode as supernovas, much of the magnesium is expelled into the interstellar medium where it may recycle into new star systems. Magnesium is the eighth most abundant element in the Earth's crust[13] and the fourth most common element in the Earth (after iron, oxygen and silicon), making up 13% of the planet's mass and a large fraction of the planet's mantle. It is the third most abundant element dissolved in seawater, after sodium and chlorine.[14]
This element is the eleventh most abundant element by mass in the human body and is essential to all cells and some 300 enzymes.[15] Magnesium ions interact with polyphosphate compounds such as ATP, DNA, and RNA. Hundreds of enzymes require magnesium ions to function. Magnesium compounds are used medicinally as common laxatives and antacids (such as milk of magnesia), and to stabilize abnormal nerve excitation or blood vessel spasm in such conditions as eclampsia.[15]
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