Article: Magnesium

12 sodium ← magnesium → aluminium Be ↑ Mg ↓ Ca periodic table
General
Name, Symbol, Number	magnesium, Mg, 12
Chemical series	alkaline earth metals
Group, Period, Block	2, 3, s
Appearance	silvery white
Atomic mass	24.3050(6) g/mol
Electron configuration	[Ne] 3s2
Electrons per shell	2, 8, 2
Physical properties
Phase	solid
Density (near r.t.)	1.738 g·cm−3
Liquid density at m.p.	1.584 g·cm−3
Melting point	923 K (650 °C, 1202 °F)
Boiling point	1363 K (1090 °C, 1994 °F)
Heat of fusion	8.48 kJ·mol−1
Heat of vaporization	128 kJ·mol−1
Heat capacity	(25 °C) 24.869 J·mol−1·K−1
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 701 773 861 971 1132 1361
Atomic properties
Crystal structure	hexagonal
Oxidation states	2 (strongly basic oxide)
Electronegativity	1.31 (Pauling scale)
Ionization energies (more)	1st: 737.7 kJ·mol−1
	2nd: 1450.7 kJ·mol−1
	3rd: 7732.7 kJ·mol−1
Atomic radius	150 pm
Atomic radius (calc.)	145 pm
Covalent radius	130 pm
Van der Waals radius	173 pm
Miscellaneous
Magnetic ordering	paramagnetic
Electrical resistivity	(20 °C) 43.9 nΩ·m
Thermal conductivity	(300 K) 156 W·m−1·K−1
Thermal expansion	(25 °C) 24.8 µm·m−1·K−1
Speed of sound (thin rod)	(r.t.) (annealed) 4940  m·s−1
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
CAS registry number	7439-95-4
Notable isotopes
Main article: Isotopes of magnesium iso NA half-life DM DE (MeV) DP 24Mg 78.99% Mg is stable with 12 neutrons 25Mg 10% Mg is stable with 13 neutrons 26Mg 11.01% Mg is stable with 14 neutrons
References

Magnesium is the chemical element in the periodic table that has the symbol Mg and atomic number 12 and an atomic mass of 24.31. Magnesium is the eighth most abundant element and constitutes about 2% of the Earth's crust by weight, and it is the third most plentiful element dissolved in seawater. The free element (metal) is not found in nature. Once produced from magnesium salts, this alkaline earth metal is primarily used as an alloying agent to make aluminium-magnesium alloys, sometimes called "magnalium" or "magnelium".

Isotopes

²⁶Mg is a stable isotope that has found application in isotopic geology, similar to that of aluminium. ²⁶Mg is a radiogenic daughter product of ²⁶Al, which has a half-life of 717,000 years. Large enrichments of stable ²⁶Mg have been observed in the Ca-Al-rich inclusions of some carbonaceous chondrite meteorites. The anomalous abundance of ²⁶Mg is attributed to the decay of its parent ²⁶Al in the inclusions. Therefore, the meteorite must have formed in the solar nebula before the ²⁶Al had decayed. Hence, these fragments are among the oldest objects in the solar system and have preserved information about its earliest history.

It is conventional to plot ²⁶Mg/²⁴Mg against an Al/Mg ratio. In an isochrone plot, the Al/Mg ratio plotted is²⁷Al/²⁴Mg. The slope of the isochron has no age significance, but indicates the initial ²⁶Al/²⁷Al ratio in the sample at the time when the systems were separated from a common reservoir.

Notable characteristics of element and compounds

Elemental magnesium is a fairly strong, silvery-white, light-weight metal (two thirds the density of aluminium). It slightly tarnishes when exposed to air, although unlike the alkaline metals, storage in an oxygen free environment is unnecessary because magnesium is protected by a thin layer of oxide which is fairly impermeant and hard to remove. Like its lower periodic table group neighbor calcium, magnesium reacts with water at room temperature, though it reacts much more slowly than calcium. When it is submerged in water hydrogen bubbles will almost unnoticably begin to form on the surface of the metal, though if powdered it will react much more rapidly. The reaction will occur faster with higher temperatures (see precautions). Magnesium is a highly flammable metal, but while it is easy to ignite when powdered or shaved into thin strips, it is difficult to ignite in mass or bulk. Once ignited it is difficult to extinguish, being able to burn in both nitrogen (forming magnesium nitride), and carbon dioxide (forming magnesium oxide and carbon).

Magnesium, when it burns in air, produces a brilliant white light. This was used in the early days of photography when magnesium powder was used as a source of illumination (flash powder). Later, magnesium ribbon was used in electrically ignited flash bulbs. Magnesium powder is still used in the manufacture of fireworks and marine flares where a brilliant white light is required.

Magnesium, when glowing white, has many chemical properties that it does not possess at lower temperatures. It also becomes more toxic, although this is irrelevant because the high temperature alone is extremely dangerous.

Magnesium compounds are typically white crystals. Most are soluble in water, providing the sour-tasting magnesion ion Mg²⁺. Small amounts of dissolved magnesium ion contributes to the tartness and taste of natural waters. Magnesium ion in large amounts is an ionic laxitive, and magnesium sulfate (Epsom salts) is sometimes used for this purpose. So-called "milk of magnesia" is a water suspension of one of the few insoluble magnesium compounds, magnesium hydroxide; the undissolved particles give rise to its appearance and name. Milk of magnesia is a mild base, and is commonly used as an antacid.

History

The name originates from the Greek word for a district in Thessaly called Magnesia. Joseph Black in England recognized magnesium as being an element in 1755, Sir Humphry Davy electrolytically isolated pure magnesium metal in 1808 from a mix of magnesia and HgO, and A. A. B. Bussy prepared it in coherent form in 1831. Magnesium is the eighth most abundant element in the earth's crust. It is an alkaline earth metal and therefore does not occur uncombined with other elements. It is found in large deposits of magnesite, dolomite, and other minerals.