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Magnesium is a chemical element with symbol Mg and atomic number 12. Its common oxidation number is +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole. Magnesium is the fourth most common element in the Earth as a whole, making up 13% of the planet's mass and a large fraction of the planet's mantle. Due to magnesium ion's high solubility in water, it is the third most abundant element dissolved in seawater.
In human biology, magnesium is the eleventh most abundant element by mass in the human body; its ions are essential to all living cells, where they play a major role in manipulating important biological polyphosphate compounds like ATP, DNA, and RNA. Hundreds of enzymes thus require magnesium ions to function. Magnesium compounds are used medicinally as common laxatives, antacids (e.g., milk of magnesia), and in a number of situations where stabilization of abnormal nerve excitation and blood vessel spasm is required (e.g., to treat eclampsia). Magnesium ions are sour to the taste, and in low concentrations they help to impart a natural tartness to fresh mineral waters.
In vegetation magnesium is the metallic ion at the center of chlorophyll, and is thus a common additive to fertilizers.
Physical and chemical properties
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 nitrogen (forming magnesium nitride), carbon dioxide (forming magnesium oxide and carbon) and water (forming magnesium oxide and hydrogen). This property was used in incendiary weapons used in the firebombing of cities in World War II, the only practical civil defense being to smother a burning flare under dry sand to exclude the atmosphere. On burning in air, magnesium produces a brilliant white light which includes strong ultraviolet. Thus magnesium powder (flash powder) was used as a source of illumination in the early days of photography. Later, magnesium ribbon was used in electrically ignited flash bulbs. Magnesium powder is used in the manufacture of fireworks and marine flares where a brilliant white light is required. Flame temperatures of magnesium and magnesium alloys can reach 3,100 °C (3,370 K; 5,610 °F), although flame height above the burning metal is usually less than 300 mm (12 in). Magnesium may be used as an ignition source for thermite, an otherwise difficult to ignite mixture of aluminium and iron oxide powder.
Application:
Magnesium is the third most commonly used structural metal, following iron and aluminium. It has been called the lightest useful metal by The Periodic Table of Videos.
The main applications of magnesium are, in order: component of aluminium alloys, in die-casting (alloyed with zinc), to remove sulfur in the production of iron and steel, the production of titanium in the Kroll process.
Magnesium, in its purest form, can be compared with aluminium, and is strong and light, so it is used in several high volume part manufacturing applications, including automotive and truck components. Specialty, high-grade car wheels of magnesium alloy are called "mag wheels", although the term is often more broadly misapplied to include aluminum wheels.
As metal:
The second application field of magnesium is electronic devices. Because of low weight, good mechanical and electrical properties, magnesium is widely used for manufacturing of mobile phones, laptop and tablet computers, cameras, and other electronic components.
In magnesium compounds
Magnesium compounds, primarily magnesium oxide (MgO), are used as a refractory material in furnace linings for producing iron, steel, nonferrous metals, glass and cement. Magnesium oxide and other magnesium compounds are also used in the agricultural, chemical, and construction industries.
Magnesium reacted with an alkyl halide gives a Grignard reagent, which is a very useful tool for preparing alcohols.
In agriculture and biology, the magnesium ion is necessary for all life (see magnesium in biology), so magnesium salts are frequently included in various foods, fertilizers (magnesium is a component of chlorophyll), and culture media.
Niche and illustrative uses of magnesium compounds
Biological
Pharmaceutical preparations of magnesium are used to treat magnesium deficiency and hypomagnesemia, as well as eclampsia. Usually in lower dosages, magnesium is commonly included in dietary mineral preparations, including many multivitamin preparations.
Sorted by type of magnesium salt, biological applications of magnesium include:
Magnesium sulfate, as the heptahydrate called Epsom salts, is used as bath salts, as a laxative, and as a highly soluble fertilizer.
Magnesium hydroxide, suspended in water, is used in milk of magnesia antacids and laxatives.
Magnesium chloride, oxide, gluconate, malate, orotate, glycinate and citrate are all used as oral magnesium supplements. Oral magnesium supplements have been claimed to be therapeutic for some individuals who suffer from Restless Leg Syndrome (RLS).
Magnesium borate, magnesium salicylate, and magnesium sulfate are all used as antiseptics.
Magnesium bromide is used as a mild sedative (this action is due to the bromide, not the magnesium).
Magnesium stearate is a slightly flammable white powder with lubricating properties. In pharmaceutical technology, it is used in the manufacturing of numerous kinds of tablets to prevent the tablets from sticking to the equipment during the tablet compression process (i.e., when the tablet's substance is pressed into tablet form).
Magnesium carbonate powder is used by athletes such as gymnasts, weightlifters and climbers to eliminate moisture and improving the grip on a gymnastic apparatus, lifting bar and climbing rocks.
Non biological
Dead-burned magnesite (magnesium oxide) is used for refractory purposes such as brick and liners in furnaces and converters.
Magnesium oxide from calcination is used as an electrical insulator in fire-resistant cables.
Magnesium sulfite is used in the manufacture of paper (sulfite process).
Magnesium phosphate is used to fireproof wood used in construction.
Magnesium hexafluorosilicate is used in mothproofing of textiles.
In the form of turnings or ribbons, Mg is useful in purification of solvents, for example the preparation of super-dry ethanol
Biological role
Main article: Magnesium in biology
Because of the important interaction between phosphate and magnesium ions, magnesium ions are essential to the basic nucleic acid chemistry of life, and thus are essential to all cells of all known living organisms. Over 300 enzymes require the presence of magnesium ions for their catalytic action, including all enzymes utilizing or synthesizing ATP, or those that use other nucleotides to synthesize DNA and RNA. ATP exists in cells normally as a chelate of ATP and a magnesium ion.
Plants have an additional use for magnesium in that chlorophylls are magnesium-centered porphyrins. Magnesium deficiency in plants causes late-season yellowing between leaf veins, especially in older leaves, and can be corrected by applying Epsom salts (which is rapidly leached), or else crushed dolomitic limestone to the soil.
Magnesium Oxide