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.
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.
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
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 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
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
Magnesium bromide is used as a mild sedative (this action is due to the bromide, not
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.
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
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
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