Magnesium

Magnesium, ₁₂Mg
General properties
Pronunciation	/mæɡˈniːziəm/ (mag-NEE-zee-əm)
Appearance	shiny grey solid
Standard atomic weight (Ar, standard)	[24.304, 24.307] conventional: 24.305
Magnesium in the periodic table
	sodium ← magnesium → aluminium
Atomic number (Z)	12
Group	group 2 (alkaline earth metals)
Period	period 3
Element category	alkaline earth metal
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 (near r.t.)	1.738 g/cm3
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 J/(mol·K)
Atomic properties
Oxidation states	+2, +1(a strongly basic oxide)
Electronegativity	Pauling scale: 1.31
Ionization energies	1st: 737.7 kJ/mol; 2nd: 1450.7 kJ/mol; 3rd: 7732.7 kJ/mol; (more);
Atomic radius	empirical: 160 pm
Covalent radius	141±7 pm
Van der Waals radius	173 pm
	Spectral lines
	Spectral lines
Miscellanea
Crystal structure	hexagonal close-packed (hcp)
Speed of sound thin rod	4940 m/s (at r.t.) (annealed)
Thermal expansion	24.8 µm/(m·K) (at 25 °C)
Thermal conductivity	156 W/(m·K)
Electrical resistivity	43.9 nΩ·m (at 20 °C)
Magnetic ordering	paramagnetic
Magnetic susceptibility	+13.1·10−6 cm3/mol (298 K)
Young's modulus	45 GPa
Shear modulus	17 GPa
Bulk modulus	35.4 GPa
Poisson ratio	0.290
Mohs hardness	1–2.5
Brinell hardness	44–260 MPa
CAS Number	7439-95-4
History
Naming	after Magnesia, Greece
Discovery	Joseph Black (1755)
First isolation	Humphry Davy (1808)
Main isotopes of magnesium
	view; talk; edit; \| references \| in Wikidata

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: all group 2 elements have the same electron configuration in the outer electron shell and a similar crystal structure.

Magnesium is the ninth most abundant element in the universe. It is produced in large, aging stars from 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 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.

Magnesium occurs naturally only in combination with other elements, where it invariably has a +2 oxidation state. The free element (metal) can be produced artificially, and is highly reactive (though in the atmosphere, it is soon coated in a thin layer of oxide that partly inhibits reactivity — see passivation). The free metal burns with a characteristic brilliant-white light. The metal is now obtained mainly by electrolysis of magnesium salts obtained from brine, and is used primarily as a component in aluminium-magnesium alloys, sometimes called magnalium or magnelium. Magnesium is less dense than aluminium, and the alloy is prized for its combination of lightness and strength.

Magnesium is the eleventh most abundant element by mass in the human body and is essential to all cells and some 300 enzymes. 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, antacids (e.g., milk of magnesia), and to stabilize abnormal nerve excitation or blood vessel spasm in such conditions as eclampsia.