12
  Mg  
24.305000
Magnesium

Name: Magnesium
Symbol: Mg
Atomic Number: 12
Atomic Weight: 24.305000
Family: Alkaline Earth Metals
CAS RN: 7439-95-4
Description: Grayish-white metal. Reacts with hot water and burns in air when ignited.
State (25C): Solid
Oxidation states: +2

Molar Volume: 13.97 cm3/mole
Valence Electrons: 3s2

Boiling Point:  1363K, 1090C, 1994F
Melting Point:
922K, 649C,  200F
Electrons Energy Level: 2, 8, 2
Isotopes: 15 + 3 Stable
Heat of Vaporization: 127.4 kJ/mol
Heat of Fusion: 8.954 kJ/mol
Density: 1.738 g/cm3 @ 300K
Specific Heat: 1.02 J/gK
Atomic Radius: 1.72
Ionic Radius: 0.72
Electronegativity: 1.31 (Pauling); 1.23 (Allrod Rochow)
Vapor Pressure: 361 Pa @ 649C
4
Be
9.012
The name originates from the Greek word for a district in Thessaly called Magnesia.  It is related to Magnetite and Manganese, which also originated from this area, and required differentiation as separate substances.

Joseph Black in Scotland recognized Magnesium as being an element in 1755, Sir Humpry Davy electrolytically isolated pure Magnesium metal in 1808 from a mix of Magnesia and HgO, and A.A. 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.  In 1618 a farmer at Epsom in England attempted to give his cows water from a well.  This they refused to drink because of the water's bitter taste. However the farmer noticed that the water seemed to heal scratches and rashes.  The fame of Epsom salts spread.   Eventually they were recognised to be Magnesium Sulphate, MgSO4.  Black recognized Magnesium as an element in 1755.  It was isolated by Davy in 1808 who electrolysed a mixture of Magnesia (Magnesium Oxide, MgO) and Mercuric Oxide (HgO). Davy's first suggestion for a name was Magnium but the name Magnesium is now used.

Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. 

12
Mg
24.30
20
Ca
40.07
38
Sr
87.62
56
Ba
137.3
88
Ra
226.0

Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions).  This was further evidence for atoms.  Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about Strontium Oxalates published in the Philosophical Transactions.  Dalton published these ideas himself in the following year in the New System of Chemical Philosophy.

Humprey_davy.jpg (4729 bytes)

Humphry Davy

Characteristics

1s2 2s2p6 3s2

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.  Magnesium ion is essential to all living cells. The free element (metal) is not found in nature.  Once produced from magnesium salts, this alkaline earth metal is used as an alloying agent to make Aluminum-Magnesium alloys, sometimes called "magnalium" or "magnelium".

magnesium.gif (933 bytes)

Alchemical Symbol, Magnesium

It reacts with hot water and acids. The metal is widely distributed in the environment in a number of minerals and a significant amount is found in sea water.

Elemental Magnesium is a fairly strong, silvery-white, light-weight metal (two thirds the density of Aluminum).  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 impermeable 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.  Magnesium also reacts with Hydrochloric Acid, HCl, and produces heat and Hydrogen when added to it.  The Magnesium will begin to bubble and become hot, too hot to touch comfortably.  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).

1s2
2s2 2p6
3s2

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 of little practical importance, because the high temperature alone generally prevents human contact.

magnesium1.jpg (1939 bytes) magnesium2.jpg (1410 bytes) magnesium3.jpg (1764 bytes) magnesium4.jpg (1922 bytes) magnesium5.jpg (1715 bytes)
Additional Representations of Alchemical Symbols for Magnesium

Magnesium compounds are typically white crystals.  Most are soluble in water, providing the sour-tasting magnesium 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 laxative, and Magnesium Sulfate (Epsom Salts) is sometimes used for this purpose.  So-called "Mile 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.

Occurrence

Although Magnesium is found in over 60 minerals, only Dolomite, Magnesite, Brucite, Carnallite, Talc, and Olivine are of commercial importance.

In the United States this metal is principally obtained by electrolysis of fused Magnesium Chloride from brines, wells, and sea water:

Cathode: Mg2+ + 2 e- rarrow.gif (63 bytes) Mg

Anode: 2Cl- rarrow.gif (63 bytes) Cl2 (gas) + 2 e-

The United States has traditionally been the major world supplier of this metal, supplying 45% of world production even as recently as 1995.  Today, the US market share is at 7%, with a single domestic producer left, US Magnesium, a company born from now-defunct Magcorp.  As of 2005 China has taken over as the dominant supplier, pegged at 60% world market share, which increased from 4% in 1995.  Unlike the above described electrolytic process, China is almost completely reliant on a different method of obtaining the metal from its ores, the Silicothermic Pidgeon Process (the reduction of the oxide at high temperatures with silicon).

Compounds in Living Organisms

Magnesium ion is essential to the basic nucleic acid chemistry of life, and thus is essential to all cells of all known living organisms.  Plants have an additional use for Magnesium in that chlorophylls are Magnesium-centered porphyrins.  Many enzymes require the presence of Magnesium ions for their catalytic action, especially enzymes utilizing ATP, or those which use other nucleotides to synthesize DNA and RNA.

Magnesium deficiency in humans was first described in the medical literature in 1934.   The adult human daily nutritional requirement, which is affected by various factors including gender, weight and size, is 300-400 mg/day.  Inadequate Magnesium intake frequently causes muscle spasms, and has been associated with cardiovasular disease, diabetes, high blood pressure, anxiety disordrers and osteoporosis.  Acute deficiency is rare, and is more common as a drug side effect (such as chronic alcohol or diuretic use) than from low food intake per se.  The incidence of chronic deficiency resulting in less than optimal health, is debated.

The DRI upper tolerated limit for supplemental Magnesium is 350 mg/day (calculated as mg of Mg elemental in the salt). (Supplements based on Amino Acid Chelates, Glycinate, Lysinate etc. are much better tolerated by the digestive system and do not have the side effects of the older compounds used.)  The most common symptom of excess oral Magnesium intake is diarrhea.  Since the kidneys of adult humans excrete excess Magnesium efficiently, oral Magnesium poisoning in adults with normal renal function, is very rare.  Infants, which have less ability to excrete excess Magnesium even when healthy, should not be given Magnesium supplements, except under a physician's care.

Magnesium salts (usually in the form of Magnesium Sulfate or Chloride) are used therapeutically for a number of medical conditions, especially the hypertension of eclampsia.   Magnesium is absorbed with reasonable efficiently (30% to 40%) by the body from any soluble Magnesium salt, such as the chloride or citrate.  Magnesium is similarly absorbed from epsom salts, although the sulfate in these salts adds to their laxative effect at higher doses.  Magnesium absorption from the insoluble oxide and hydroxide salts (Milk of Magnesia) is erratic and of poorer efficiency, since it depends on the neutralization and solution of the salt by the acid of the stomach, which may not be (and usually is not), complete.

Food Sources

Green vegetables such as spinach provide Magnesium because the center of the chlorophyll molecule contains magnesium.  Nuts (especially cashews and almonds), seeds and some whole grains are also good sources of magnesium.

Although magnesium is present in many foods, it usually occurs in dilute form.  As with most nutrients, daily needs for magnesium are unlikely to be met from a single serving of any single food.  Eating a wide variety of foods, including five servings of fruits and vegetables daily and plenty of whole grains, helps to ensure an adequate intake of magnesium.

Because magnesium readily dissolves in the water used to refine foods, and also in the water-rich parts of certain foods which are removed during refining, the magnesium content of many refined foods is low.  Whole-wheat bread, for example, has twice as much magnesium as white bread because the magnesium-rich germ and bran are removed when white flour is processed. The table of food sources of magnesium suggests many dietary sources of magnesium.

Water can provide magnesium, but the amount varies according to the water supply.   "Hard" water contains more magnesium than "soft" water.   Dietary surveys do not estimate magnesium intake from water, which may lead to underestimating total magnesium intake and its variability.

Too much magnesium may make it difficult for the body to absorb calcium.  Not enough magnesium can lead to hypomagnesemia with irregular heartbeats, high blood pressure (a sign in humans but not some experimental animals such as rodents), insomnia and muscle spasms (fasciculation).  However, as noted, symptoms of low magnesium from pure dietary deficiency are thought to be rarely encountered.

Following are some foods and the amount of magnesium in them:

  • spinach (1/2 cup) = 80 milligrams (mg)
  • peanut butter (2 tablespoons) = 50 mg
  • black-eyed peas (1/2 cup) = 45 mg
  • milk: low fat (1 cup) = 40 mg
The U.S. RDA/RDV is 400 mg of magnesium.

Applications

As a Metal

Magnesium is the third most commonly used structural metal, following steel and aluminum.

Magnesium compounds, primarily magnesium oxide, are used mainly as refractory material in furnace linings for producing iron, steel, nonferrous metals, glass and cement.   Magnesium oxide and other compounds also are used in agricultural, chemical and construction industries.  As a metal, this element's principal use is as an alloying additive to aluminum with these aluminum-magnesium alloys being used mainly for beverage cans.

Magnesium, in its purest form, can be compared to aluminum, 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".  In 1957 a Corvette SS, designed for racing, was constructed with magnesium body panels.  Volkswagen has used magnesium in its engine components for many years.  For a long time, Porsche used magnesium alloy for its engine blocks due to the weight advantage.  There is renewed interest in magnesium engine blocks, as featured in the 2006 BMW 325i and 330i models.  The BMW engine uses an aluminum alloy insert for the cylinder walls and cooling jackets surrounded by a high temperature magnesium alloy AJ62A . The application of magnesium AE44 alloy in the 2006 Corvette Z06 engine cradle has advanced the technology of designing robust automotive parts in magnesium.  Both of these alloys are recent developments in high temperature low creep magnesium alloys.  The general strategy for such alloys is to form intermetallic precipitates at the grain boundaries, for example by adding mischmetal or calcium.  New alloy development and lower costs, which are becoming competitive to aluminum, will further the number of automotive applications.

In December 2005, for the first time on record, the automotive grade magnesium alloy price per cm dropped below the A380 aluminum alloy price per cm.

The second application field of magnesium is electronic devices.  Due to low weight, good mechanical and electrical properties, magnesium is widely used for manufacturing of mobile phones, laptop computers, cameras, and other electronic components.

Historically, magnesium was one of the main aerospace construction metals and was used for German military aircraft as early as World War I and extensively for German aircraft in World War II. The Germans coined the name 'Elektron' for magnesium alloy which is still used today.  Due to perceived hazards with magnesium parts in the event of fire, the application of magnesium in the commercial aerospace industry was generally restricted to engine related components.  Currently the use of magnesium alloys in aerospace is increasing, mostly driven by the increasing importance of fuel economy and the need to reduce weight.  The development and testing of new magnesium alloys notably Elektron 21 which has successfully undergone extensive aerospace testing for suitability in both engine, internal and airframe components.  European Community runs three R&D magnesium projects in Aerospace priority of Six Framework Program.

Other Uses

Supplements

Autism

According to a recent online survey, approximately 30% of parents give their autistic children a supplement of magnesium and vitamin B6 (Green 2006).  There are conflicting studies as to whether or not this is an effective therapy for autism (Martineau 1985, Tolbert 1993, Findling 1997, Lelord 1981).  There is no stantardization of what dosages of magnesium and vitamin B6, or types of magnesium should be used.  If it is an effective therapy, variance of dosages and preparations used may be affecting the findings of studies.  The aim of magnesium supplementation being the normalizarion of low levels in tissues, appopriate assays, such as erythrocyte magnesium measurements, should be used in dose ranging studies.  One poorly controlled study showed positive and significant behavioral effects of combined vitamin B6 and magnesium therapy, but not vitamin B6 or magnesium.

Mousain-Bosc and colleagues (2006) showed that children with autism - pervasive developmental disorder (PDD) (n = 33) had significantly lower red blood cell magnesium levels than controls (n = 36).  Intervention with magnesium and vitamin B6 (pyridoxine) reduced PDD symptoms in 23 children out of 33, stereotyped restricted behavior (18 children), and abnormal/delayed functioning (17 children); it improved social interactions in 23 children and communication in 24 children.

Attention Deficit Hyperactivity Disorder (ADHD)

Mousain-Bosc and colleagues (2006) showed that children with ADHD (n = 46) had significantly lower red blood cell magnesium levels than controls (n = 30).   Intervention with magnesium and vitamin B6 (pyridoxine) reduced hyperactivity, hyperemotivity/aggressiveness and improved school attention.

Compounds

Dolomite, CaCO3MgCO3 Carnallite, KClMgCl26H2O
Magnesium Carbonate, MgCO3 Magnesium Fluoride, MgF2
Magnesium Phosphate, Mg3(PO4)2
Epsom Salts, Magnesium Sulphate (MgSO47H2O)
Milk of Magnesia, Magnesium Hydroxide Mg(OH)2
Magnesia, Magnesium Oxide MgO
Magnesium Stearate, Mg(C18H35O2)2

Isotopes

26Mg is a stable isotope that has found application in isotopic geology, similar to that of Aluminum.  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 meterorites.  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 early history.

It is conventional to plot 26Mg/24Mg against an Al/Mg ratio.   In an isochron dating 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.

atom.gif (700 bytes)

Isotope Atomic Mass Half-Life
Mg20 20.0189 95 ms
Mg21 21.0117 122 ms
Mg22 21.9996 3.857 seconds
Mg23 22.9941 11.317 seconds
Mg24 23.985 Stable
Mg25 24.9858 Stable
Mg26 25.9826 Stable
Mg27 26.9843 9.458 minutes
Mg28 27.9839 20.91 hours
Mg29 28.9886 1.3 seconds
Mg30 29.9905 335 ms
Mg31 30.9965 230 ms
Mg32 31.999 120 ms
Mg33 33.006 90 ms
Mg34 34.009 20 ms
Mg35 35.017 >200 ns
Mg36 36.022 >200 ns
Mg37 37.031 > 260 ns

Precautions

80px-Flammable.jpg (2186 bytes) Magnesium metal and alloys are highly flammable in their pure form when molten, as a powder, or in ribbon form.  Burning or molten Magnesium metal reacts violently with water.  Magnesium powder is an explosive hazard. 

One should wear safety glasses while working with Magnesium.  The bright white light (including ultraviolet) produced by burning Magnesium can damage the eyes.   Water should not be used to extinguish Magnesium fires, because it can actually feed the fire, according to the reaction:

Mg (s) + 2H2O (g) rarrow.gif (63 bytes) Mg(OH)2 (aq) + H2 (g)

or in words:

Magnesium (solid) + Steam rarrow.gif (63 bytes) Magnesium Hydroxide (aq) + Hydrogen (gas)

Carbon Dioxide fire extinguishers should not be used either, because Magnesium can burn in Carbon Dioxide (forming Magnesium Oxide, MgO, and Carbon.  A Class D dry chemical fire extinguisher should be used if available, or else the fire should be covered with sand or Magnesium foundry flux.  An easy way to put out small metal fires is to place a polyethene bag filled with dry sand on top of the fire. The heat of the fire will melt the bag and the sand will flow out onto the fire.


atom.gif (700 bytes)

Magnesium Data

 

Atomic Structure

Atomic Radius (): 1.72
Atomic Volume cm3/mol : 13.97cm3/mol
Covalent Radius: 1.36
Crystal Structure: Hexagonal
Ionic Radius: 0.72

Chemical Properties

Electrochemical Equivalents: 0.45341 g/amp-hr
Electron Work Function: 3.66eV
Electronegativity: 1.31 (Pauling); 1.23 (Allrod Rochow)
Heat of Fusion: 8.954 kJ/mol
Incompatibilities: unknown
First Ionization Potential: 7.646
Second Ionization Potential: 15.035
Third Ionization Potential: 80.143
Valence Electron Potential(-eV): 40
Ionization Energy (eV): 7.646 eV

Physical Properties

Atomic Mass Average: 24.305
Boiling Point: 1363K, 1090C, 1994F
Melting Point: 922K, 649C,  200F
Heat of Vaporization: 127.4 kJ/mol
Coefficient of Lineal Thermal Expansion/K-1: 26.1E-6
Electrical Conductivity: 0.226 106/cm
Thermal Conductivity: 1.56 W/cmK
Density: 1.738 g/cm3 @ 300K
Elastic Modulus (Bulk): 35.6/GPa
Elastic Modulus (Rigidity): 17.3/GPa
Elastic Modulus Youngs: 44.7/GPa
Enthalpy of Atomization: 148.5 kJ/mole @ 25C
Enthalpy of Fusion: 8.95 kJ/mole
Enthalpy of Vaporization: 128.7 kJ/mole
Hardness Scale (Brinell): 260 MN m-2
Hardness Scale (Mohs): 2.5
Hardness Scale (Vickers): unknown
Flammability Class: unknown
Molar Volume: 13.97 cm3/mole
Optical Reflectivity: 74%
Optical Refractive Index: unknown
Relative Gas Density (Air=1): unknown
Specific Heat: 1.02 J/gK
Vapor Pressure: 361 Pa @ 649C
Estimated Crustal Abundance: 2.33104 milligrams per kilogram
Estimated Oceanic Abundance:
1.29103 milligrams per liter


(Magnesia, district in Thessaly) Compounds of magnesium have long been known. Black recognized magnesium as an element in 1755. It was isolated by Davy in 1808, and prepared in coherent form by Bussy in 1831. Magnesium is the eighth most abundant element in the earth's crust. It does not occur uncombined, but is found in large deposits in the form of magnesite, dolomite, and other minerals. the metal is now principally obtained in the U.S. by electrolysis of fused magnesium chloride derived from brines, wells, and sea water. Magnesium is a light, silvery-white, and fairly tough metal. It tarnishes slightly in air, and finely divided magnesium readily ignites upon heating in air and burns with a dazzling white flame. It is used in flashlight photography, flares, and pyrotechnics, including incendiary bombs. It is on third lighter than aluminium, and in alloys is essential for airplane and missile construction. the metal improves the mechanical, fabrication, and welding characteristics of aluminum when used as an alloying agent. magnesium is used in producing nodular graphite in cast iron, and is used as an additive to conventional propellants. It is also used as a reducing agent in the production of pure uranium and other metals from their salts. The hydroxide (milk of magnesia), chloride, sulfate (Epsom salts), and citrate are used in medicine. Dead-burned magnesite is employed for refractory purposes such as brick and liners in furnaces and converters. Organic magnesium compounds are important. Magnesium is an important element in both plant and animal life. Chlorophylls are magnesium-centered perphyrins. The adult daily requirement of magnesium is about 300 mg/day, but this is affected by various factors. Great care should be taken in handling magnesium metal, especially in the finely divided state, as serious fires can occur. Water should not be used on burning magnesium or on magnesium fires.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond


Although it is the eighth most abundant element in the universe and the seventh mostabundant element in the Earth's crust, magnesium is never found free in nature. Magnesium was first isolated by Sir Humphry Davy, an English chemist, through the electrolysis of a mixture of magnesium oxide (MgO) and mercuric oxide (HgO) in 1808.   Today, magnesium can be extracted from the minerals dolomite (CaCO3MgCO3) and carnallite (KClMgCl26H2O), but is most often obtained from seawater. Every cubic kilometer of seawater contains about 1.3 billion kilograms of magnesium (12 billion pounds per cubic mile).

Magnesium burns with a brilliant white light and is used in pyrotechnics, flares and photographic flashbulbs. Magnesium is the lightest metal that can be used to build things, although its use as a structural material is limited since it burns at relatively low temperatures. Magnesium is frequently alloyed with aluminum, which makes aluminum easier to roll, extrude and weld. Magnesium-aluminum alloys are used where strong, lightweight materials are required, such as in airplanes, missiles and rockets. Cameras, horseshoes, baseball catchers' masks and snowshoes are other items that are made from magnesium alloys.

Magnesium oxide (MgO), also known as magnesia, is the second most abundant compound in the Earth's crust.  Magnesium oxide is used in some antacids, in making crucibles and insulating materials, in refining some metals from their ores and in some types of cements. When combined with water (H2O), magnesia forms magnesium hydroxide (Mg(OH)2), better known as milk of magnesia, which is commonly used as an antacid and as a laxative.

Hydrated magnesium sulphate (MgSO47H2O), better known as Epsom salt, was discovered in 1618 by a farmer in Epsom, England, when his cows refused to drink the water from a certain mineral well. He tasted the water and found that it tasted very bitter. He also noticed that it helped heal scratches and rashes on his skin. Epsom salt is still used today to treat minor skin abrasions.

Other magnesium compounds include magnesium carbonate (MgCO3) and magnesium fluoride (MgF2). Magnesium carbonate is used to make some types of paints and inks and is added to table salt to prevent caking. A thin film of magnesium fluoride is applied to optical lenses to help reduce glare and reflections.