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A light, silvery-white, moderately hard metallic element that in ribbon or powder form burns with a brilliant white flame. It is used in structural alloys, pyrotechnics, flash photography, and incendiary bombs. Atomic number 12; atomic weight 24.305; melting point 649°C; boiling point 1,090°C; specific gravity 1.74 (at 20°C); valence 2.
[From MAGNESIA.]
A metallic chemical element, Mg, in group 2 of the periodic system, atomic number 12, atomic weight 24.312. Magnesium is silvery white and extremely light in weight. The specific gravity is 1.74, and the density is 1740 kg/m3 (0.063 lb/in.3 or 108.6 lb/ft3). Because of this lightness combined with alloy strength suitable for many structural uses, magnesium has long been known as industry's lightest structural metal. See also Periodic table.
With a density only two-thirds that of aluminum, magnesium is used in countless applications where weight saving is an important consideration. The metal also has, however, many desirable chemical and metallurgical properties which account for its extensive use in a variety of nonstructural applications.
Magnesium is very abundant in nature, occurring in substantial amounts in many rock-forming minerals such as dolomite, magnesite, olivine, and serpentine. In addition, magnesium is also found in sea water, subterranean brines, and salt beds. It is the third most abundant structural metal in the Earth's crust, exceeded only by aluminum and iron.
Some of the properties of magnesium in metallic form are listed in Table 1. Magnesium is very active chemically. It will actually displace hydrogen from boiling water, and a large number of metals can be prepared by thermal reduction of their salts and oxides with magnesium. The metal will combine with most nonmetals and with practically all acids. Magnesium reacts only slightly or not at all with most alkalies and many organic chemicals, including hydrocarbons, aldehydes, alcohols, phenols, amines, esters, and most oils. As a catalyst, magnesium is useful for promoting organic condensation, reduction, addition, and dehalogenation reactions. It has long been used for the synthesis of complex and special organic compounds by the well-known Grignard reaction. Principal alloying ingredients include aluminum, manganese, zirconium, zinc, rare-earth metals, and thorium.
Property | Value |
|---|---|
Atomic number | 12 |
Atomic weight | 24.312 |
Atomic volume, cm3/g-atom | 14.0 |
Crystal structure | Close-packed hexagonal |
Electron arrangement in free atoms | (2) (8) 2 |
Mass numbers of the isotopes | 24, 25, 26 |
Percent relative abundances of 24Mg, 25Mg, 26Mg | 77, 11.5, 11.5 |
Density, g/cm3 at 20°C | 1.738 |
Specific heat, cal/g/°C at 20°C (1 cal = 4.2 joules) | 0.245 |
Melting point, °C | 650 |
Boiling point, °C | 1110 ±10 |
Magnesium compounds are used extensively in industry and agriculture. Table 2 lists the major magnesium compounds and indicates some of their more significant applications.
Compound | Uses |
|---|---|
Magnesium carbonte | Refractories, production of other magnesium compounds, water treatment, fertilizers |
Magnesium chloride | Cell feed for production of metallic magnesium, oxychloride cement, refrigerating brines, catalyst in organic chemistry, production of other magnesium compounds, flocculating agent, treatment of foliage to prevent fire and resist fire, magnesium melting and welding fluxes |
Magnesium hydroxide | Chemical intermediate, alkali, medicinal |
Magnesium oxide | Insulation, refractories, oxychloride and oxysulfate cements, fertilizers, rayon-textile processing, water treatment, papermaking, household cleaners, alkali, pharmaceuticals, rubber filler catalyst |
Magnesium sulfate | Leather tanning, paper sizing, oxychloride and oxysulfate cements, rayon delustrant, textile dyeing and printing medicinal, fertilizer ingredient, livestock-food additive, ceramics, explosives, match manufacture |
An essential mineral; present in all human tissues, especially bone. Involved in the metabolism of ATP. Present in chlorophyll and so in all green plant foods, and therefore generally plentiful in the diet. Deficiency in human beings leads to disturbances of muscle and nervous system; in cattle, to grass tetany. Magnesium-deficient plants are yellow (or chlorosed).
A metallic element essential for life and which has a number of indispensable roles in exercise. Magnesium is an important component of some of the chemicals that aid respiration (the release of energy from food). It also plays a role in the function of nerves, and the contraction of heart and other muscles. Good sources are milk, dairy products, wholegrain cereals, nuts, legumes, and leafy green vegetables, which contain magnesium within their green pigment, chlorophyll. After being absorbed, magnesium is stored in the bones. Excessive intake may cause diarrhoea. A deficiency is rare, but it can lead to neuromuscular problems. High fat diets may reduce magnesium absorption. Not all the fat can be absorbed through the small intestine. Fat remaining in the gut may bind with magnesium to form insoluble soaps which cannot pass through the intestinal wall. The magnesium may be absorbed from the colon after fermentation of the soaps by gut bacteria. However, if these are not functioning properly, serious losses of magnesium may occur. Very high calcium intakes may also interfere with the absorption of magnesium. Magnesium supplements are taken in the belief that they can offer some protection or relief from atherosclerosis, insomnia, premenstrual tension and other menstrual problems, alcoholism, insomnia, heart disorders, and, in children, hyperactivity. Magnesium has been used in some hospitals to reduce the recurrence of a heart attack. The magnesium is given as salts in solution directly into a vein during the first 24 hours after a heart attack.
An elemental metal with an atomic weight of 24.32. Magnesium is an essential nutritional substance. Deficiency produces irritability of the nervous system and trophic disturbances.
Description
Magnesium is an element (Mg) with an atomic weight of 24.312 and the atomic number 12. In its elemental form, magnesium is a light, silver-white metal. It is a cation, which means that its ion has a positive charge. Of the cations in the human body, magnesium is the fourth-most abundant. Ninety-nine percent of the body's magnesium is contained within its cells: about 60% in the bones, 20% in the muscles, 19%–20% in the soft tissue, and 1% circulates in the blood. Important to both nutrition and medicine, magnesium, like calcium and phosphorus, is considered a major mineral. Magnesium in its carbonate and sulfate forms has been used for centuries as a laxative. The name of the element comes from Magnesia, a city in Greece where large deposits of magnesium carbonate were discovered in ancient times.
Magnesium is an important element in the body because it activates or is involved in many basic processes or functions, including:
General Use
Magnesium has a number of general uses, primarily in standard allopathic medicine, but also in some alternative therapies.
Nutrition
The Food and Nutrition Board of the National Academy of Sciences has established the following dietary reference intakes (DRIs) and tolerable upper limits (ULs) for magnesium: Infants and children 0–6 months, 30 mg; 7–12 months, 75 mg; 1–3 years, 80 mg; 4–8 years, 130 mg; 9–13 years 240 mg. Males 14–18 years, 410 mg; 19–30 years, 400 mg; over 30 years, 420 mg. Females 14–18 years, 360 mg; 19–30 years, 310 mg; over 30 years, 320 mg. The ULs apply only to magnesium taken as a dietary supplement or given for medical reasons, since no toxicity from magnesium occurring naturally in foods has been reported. The ULs for magnesium are: 1–3 years, 65 mg; 4–8 years, 110 mg; 9 years and over, 350 mg.
Good dietary sources of magnesium include nuts; dried peas and beans; whole grain cereals such as oatmeal, millet, and brown rice; dark green vegetables; bone meal; blackstrap molasses; brewer's yeast; and soy products. Dark green vegetables are important sources of magnesium because it is the central atom in the structure of chlorophyll. Drinking hard water or mineral water can also add magnesium to the diet.
A severe magnesium deficiency in a healthy person is unusual because normal kidneys are very efficient in keeping magnesium levels balanced. This condition, called hypomagnesemia, is usually caused either by disease (kidney disease, severe malabsorption, chronic diarrhea, hyperparathyroidism, or chronic alcoholism) or as a side effect of certain medications, most commonly diuretics, cisplatin (a cancer medication), and a few antibiotics. The symptoms of hypomagnesemia include disturbances of the heart rhythm, muscle tremors or twitches, seizures, hyperactive reflexes, and occasional personality changes (depression or agitation). A patient with hypomagnesemia may also produce Chvostek's sign, which is a facial spasm caused when the doctor taps gently over the facial nerve. This condition of painful intermittent muscle contractions and spasms is known as tetany. Hypomagnesemia can be treated with either oral or intravenous preparations containing magnesium.
Magnesium toxicity (hypermagnesemia) is rare because excessive amounts are usually excreted in the urine and feces. Most cases of hypermagnesemia are caused by overuse of dietary supplements containing magnesium. The symptoms of magnesium toxicity include central nervous system depression, muscle weakness, fatigue, and sleepiness. In extreme cases, hypermagnesemia can cause death. It can be treated with intra-venous calcium gluconate along with respiratory support. Severe hypermagnesemia can be treated by hemodialysis or peritoneal dialysis.
Standard Medical Practice
DIAGNOSIS. The levels of magnesium in a patient's blood or body fluids can help diagnose several illnesses. A high magnesium level in the blood may indicate kidney failure, hypothyroidism, severe dehydration, Addison's disease, or overingestion of antacids containing magnesium. A low blood level of magnesium may indicate hypomagnesemia. Because 99% of the body's magnesium is contained in its cells, blood tests can only measure the approximately 1% of magnesium that is extra-cellular (circulating in the bloodstream). This makes it difficult to diagnose low magenesium levels.
Fortunately, magnesium levels in urine can also aid diagnosis. High levels of urinary magnesium may indicate overconsumption of supplemental magnesium, overuse of diuretics, hypercalcemia (too much calcium in the body), hypophosphatemia (too little phosphate in the body), or metabolic acidosis (high blood acid levels). Low levels of magnesium in the urine may point to hypomagnesemia or hypocalcemia (too little magnesium or calcium in the body), an underactive parathyroid gland, or metabolic alkalosis (high blood alkaline levels).
TREATMENT. Magnesium is used to treat tachycardia (excessively rapid heartbeat) and low levels of electrolytes (chloride, potassium, and sodium). It helps manage premature labor, and can be given prophylactically to prevent seizures in toxemia of pregnancy. In 2002, a major international study verified the effectiveness of magnesium sulfate in preventing eclampsia, a potentially fatal seizure condition in pregnant women. Not only is it effective, but at a cost of about $5 per patient, it proves less expensive as well.
Magnesium helps control seizures resulting from hypomagnesemia associated with alcoholism, Crohn's disease, or hyperthyroidism. Magnesium injections are also used to treat acute asthma attacks.
Magnesium preparations may be given as antacids in the treatment of peptic ulcers and hyperacidity. They are also given as laxatives for the short-term relief of constipation or to empty the patient's bowel prior to surgery or certain diagnostic procedures. Magnesium hydroxide is used to treat patients who have been poisoned by mineral acids or arsenic.
Magnesium in the form of magnesium sulfate is known as Epsom salts. It can be taken by mouth as a laxative, but is also used externally to reduce tissue swelling, inflammation, and itching from insect bites, heat rash, or other minor skin irritations. Epsom salts can be applied to the affected skin or body part in moist compresses, or dissolved in warm bath water.
Recent research indicates that magnesium deficiency may contribute to atherosclerosis (hardening of the arteries), as well as to necrotizing enterocolitis (NEC), a sometimes-deadly inflammation that destroys the bowel in premature infants. Magnesium may also be useful in treating attention-deficit hyperactivity disorder (ADHD) and migraine headaches.
Alternative Medicine
HOMEOPATHY. Phosphate of magnesia is a staple homeopathic remedy, called Magnesia phosphorica (Mag. phos.) It is recommended for symptoms that are relieved by the application of warmth and gentle pressure, such as hiccups accompanied by colic in infants, menstrual cramps that are relieved when the woman bends forward, and abdominal pain without nausea and vomiting. Patients who benefit from Mag. phos. are supposedly less irritable or angry in temperament than those who need Colocynthis or Chamomilla.
NATUROPATHY. Naturopaths emphasize the importance of proper food selection and preparation to obtain an adequate supply of nutrients in the diet. They maintain that modern methods of agriculture promote overcropping and soil depletion, which they believe reduces the amount of magnesium (and other minerals) available from food grown in that soil. The processing and refining of wheat and rice, which discards the magnesium contained in the bran, wheat germ, or rice husks, also reduces the amount of magnesium in these foods. For these reasons naturopaths often recommend organic produce, which they believe contains higher levels of minerals, and suggest that they not be overcooked or boiled in too much water. In addition, this water, or "pot liquor," is often rich in magnesium that cooks out of the vegetables. It should not be discarded but saved for use in soups or stews.
Many naturopaths believe that the official government recommended daily allowance (RDA) of magnesium is too low. They think that it should be doubled to about 600 or 700 mg daily for adults. Most recommend the use of dietary supplements containing magnesium to make up the difference.
Naturopathic practitioners regard magnesium to be important in the relief or cure of the following conditions:
Preparations
Dietary Supplements
Naturopaths generally recommend supplemental magnesium for people with high blood cholesterol, post-menopausal women, women taking birth control pills, diabetics, people who eat a lot of fast food or other highly processed food, and people who drink alcohol. Many nutrition experts recommend supplements that contain a balanced ratio of calcium to magnesium, usually two parts of calcium to one of magnesium. People who increase their calcium intake should increase their dose of magnesium (and phosphate) as well, because they work together and complement each other.
Some naturopaths recommend taking magnesium in the form of an aspartate or a citrate, arguing that these compounds are more easily absorbed by the body than magnesium carbonate or magnesium oxide. Others prefer magnesium chelated (combined with a metallic ion) with amino acids. Magnesium can also be obtained from herbal sources, such as red raspberries.
Standard Medical Preparations
Magnesium hydroxide is a common over-the-counter antacid, available as either a tablet or liquid. Most antacid tablets contain about 200 mg of magnesium hydroxide; liquid magnesium hydroxide is sometimes called milk of magnesia. Magnesium carbonate works as a cathartic or laxative when combined with citric acid to produce magnesium citrate; it is often flavored with lemon or cherry to make it more pleasant to swallow. Magnesium sulfate (in the form of Epsom salts) is available over the counter, usually in half-pound or pound boxes. Epsom salts are small whitish or colorless crystals that dissolve easily in water and have a bitter or salty taste.
Magnesium for intravenous dosage is prepared as a sulfate in a 50% solution. In general, intravenous administration of magnesium is reserved for patients with such serious symptoms as seizures, preeclampsia or eclampsia of pregnancy, acute asthma attacks, or severe cardiac arrhythmias. Magnesium sulfate can also be given by intramuscular injection.
Precautions
Preparations containing magnesium should not be given as laxatives to patients with kidney disease, nausea and vomiting, diarrhea, abdominal pain, rectal bleeding, symptoms of appendicitis, or symptoms of intestinal obstruction or perforation. In addition, these preparations should not be used routinely to relieve constipation, as the patient may become dehydrated, lose calcium from the body, or develop a dependence on them. Antacids containing magnesium should be used with caution in patients with kidney disease.
Side Effects
Magnesium preparations taken internally may cause hypermagnesemia, especially with prolonged use; electrolyte imbalance; and abdominal cramps when taken as a laxative. Milk of magnesia occasionally produces nausea or diarrhea. There are no known side effects of Epsom salts when used externally.
Interactions
Milk of magnesia will decrease the patient's absorption of chlordiazepoxide, digoxin, isoniazid, quinolones, or tetracycline antibiotics. Because it increases the gastrointestinal tract's mobility, magnesium can also decrease the absorption (and thereby the effectiveness) of many other drugs and supplements as well. Magnesium sulfate, if given intravenously, is incompatible with calcium gluceptate, clindamycin, dobutamine, polymyxin B sulfate, procaine, and sodium bicarbonate.
Resources
Books
Baron, Robert B., MD, MS. "Nutrition." In Current Medical Diagnosis & Treatment 2000. Edited by Lawrence M. Tierney, Jr., MD, et al. New York: Lange Medical Books/McGraw-Hill, 2000.
Beers, Mark H., MD, and Robert Berkow, MD, eds. The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 1999.
Burton Goldberg Group. Alternative Medicine: The Definitive Guide. Fife, WA: Future Medicine Publishing, Inc., 1995.
Murray, Michael, ND, and Joseph Pizzorno, ND. Encyclopedia of Natural Medicine. Rocklin, CA: Prima Publishing, 1991.
Okuda, Toshihiro, MD, PhD, Kiyoshi Kurokawa, MD, MACP, and Maxine A. Papadakis, MD. "Fluid & Electrolyte Disorders." In Current Medical Diagnosis and Treatment 2000, edited by Lawrence M. Tierney, Jr., MD et al. New York: Lange Medical Books/McGraw-Hill, 2000.
Russell, Percy J., and Anita Williams. The Nutrition and Health Dictionary. New York: Chapman & Hall, 1995.
Periodicals
"Help for Eclampsia." American Medical News (June 17, 2002): 32.
Organizations
American Association of Naturopathic Physicians. P. O. Box 20386. Seattle, WA 98112.
Committee on the Scientific Evaluation of Dietary Reference Intakes. Institute of Medicine (1997) Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academy Press, 1997.
Homeopathic Pharmacopoeia of the United States. P. O. Box 2221. Southeastern, PA 19399-2221. (610) 783-5124. Fax: (610) 783-5180. Publishes and distributes the Homeopathic Pharmacopoeia of the U.S., which defines the contents of homeopathic remedies and other preparations.
[Article by: Rebecca J. Frey, PhD; Teresa G. Odle]
For more information on magnesium, visit Britannica.com.
A gray-white, light metal (64% the weight of aluminum); easily drawn and machined; immune to alkalies.
A metallic element essential for good health. Magnesium is a constituent of coenzymes that play a role in the conversion of ATP to ADP. It also helps muscles and nerves function efficiently. Magnesium is absorbed and stored in the bones. Good dietary sources include milk, dairy products, wholegrain cereals, nuts, legumes, and especially leafy green vegetables. Excessive intakes may cause diarrhoea; a deficiency can result in neuromuscular problems. Serum magnesium levels can fall dramatically after intense activity in heat and during endurance activity (for example, decreases of 20% have been recorded after a marathon). However, this appears to be due to a redistribution of the magnesium in the body. The magnesium lost in sweat represents only a small proportion of the magnesium stored in the body, suggesting that magnesium replacement by supplementation after exercise is probably not necessary.
Properties
Magnesium is a ductile, silver-white, chemically active metal with a hexagonal close-packed crystalline structure. It is malleable when heated. Magnesium is one of the alkaline-earth metals in Group 2 of the periodic table. It reacts very slowly with cold water. It is not affected by dry air but tarnishes in moist air, forming a thin protective coating of basic magnesium carbonate, MgCO3·Mg(OH)2. When heated, magnesium powder or ribbon ignites and burns with an intense white light and releases large amounts of heat, forming the oxide, magnesia, MgO. A magnesium fire cannot be extinguished by water, since water reacts with hot magnesium and releases hydrogen. Magnesium reacts with the halogens and with almost all acids. It is a powerful reducing agent and is used to free other metals from their anhydrous halides.
Compounds
Magnesium forms many compounds. The oxide, hydroxide, chloride, carbonate, and sulfate are commercially important. They are used in ceramics, cosmetics, fertilizers, insulation, leather tanning, and textile processing. Epsom salts (magnesium sulfate heptahydrate, MgSO4·7H2O), milk of magnesia (magnesium hydroxide, Mg(OH)2), and citrate of magnesia are used in medicine. Magnesium reacts with organic halides to form the Grignard reagents of organic chemistry.
Natural Occurrence
Magnesium is the eighth most abundant element in the earth's crust but does not occur uncombined in nature. It is found in abundance in the minerals brucite, magnesite, dolomite, and carnalite. It is also found (as the silicate) in asbestos, meerschaum, serpentine, and talc. Magnesium chloride is found in seawater, brines, and salt wells. Mineral waters often contain salts of magnesium; the magnesium ion imparts a bitter flavor. Magnesium is a constituent of the chlorophyll in green plants and is necessary in the diet of animals and humans.
Commercial Preparation
Two methods of producing magnesium commercially are used. The principal method is the electrolysis of fused magnesium chloride, which is used in the extraction of magnesium from seawater (the principal source) and from dolomite. In recovery from seawater, the magnesium is precipitated as magnesium hydroxide by treatment with lime (calcium oxide) obtained from oyster shells. The hydroxide is collected and treated with hydrochloric acid to form the chloride. The chloride is fused and electrolyzed, forming magnesium metal and chlorine gas. The molten metal is cast into ingots for further processing; the chlorine gas is made into hydrochloric acid and is reused to form magnesium chloride. About 1 lb of magnesium is recovered from each 100 gal of seawater; the oceans are a virtually inexhaustible source of this metal. A second method of magnesium production, called the ferrosilicon process, involves the reduction of magnesium oxide (prepared by calcining dolomite) with an iron-silicon alloy.
Uses
Magnesium is a commercially important metal with many uses. It is only two thirds as dense as aluminum. It is easily machined, cast, forged, and welded. It is used extensively in alloys, chiefly with aluminum and zinc, and with manganese. Magnesium alloys were used as early as 1910 in Germany. Early structural uses of magnesium alloys were in aircraft fuselages, engine parts, and wheels. They are now also used in jet-engine parts, rockets and missiles, luggage frames, portable power tools, and cameras and optical instruments. Duralumin and magnalium are alloys of magnesium. The metal is also used in pyrotechnics, especially in incendiary bombs, signals, and flares, and as a fuse for thermite. It is used in photographic flashbulbs and is added to some rocket and missile fuels. It is used in the preparation of malleable cast iron. An important use is in preventing the corrosion of iron and steel, as in pipelines and ship bottoms. For this purpose a magnesium plate is connected electrically to the iron. The rapid oxidation of the magnesium prevents the slower oxidation and corrosion of the iron.
A chemical element, atomic number 12, atomic weight 24.312, symbol Mg. See Table 6. Its salts are essential in nutrition, being required for the activity of many enzymes, especially those concerned with oxidative phosphorylation. It is found in the intra- and extracellular fluids and is excreted in urine and feces.
An element with atomic number 12; symbol: Mg. Magnesium is contained in the minerals olivine and pyroxene, and is very abundant in the mantles of the inner planets.
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| Name, symbol, number | magnesium, Mg, 12 | ||||||||||||||||||||||||
| Chemical series | alkaline earth metals | ||||||||||||||||||||||||
| Group, period, block | 2, 3, s | ||||||||||||||||||||||||
| Appearance | silvery white solid at room temp |
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| Standard atomic weight | 24.3050(6) g·mol−1 | ||||||||||||||||||||||||
| 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 ° |
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| Boiling point | 1363 K (1090 °C, 1994 ° |
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| 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 | ||||||||||||||||||||||||
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| Atomic properties | |||||||||||||||||||||||||
| Crystal structure | hexagonal | ||||||||||||||||||||||||
| Oxidation states | 2 (strongly basic oxide) |
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| 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 |
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| 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 | ||||||||||||||||||||||||
| Selected isotopes | |||||||||||||||||||||||||
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Magnesium has the symbol Mg, the atomic number 12, and an atomic mass of 24.31. Magnesium is the ninth most abundant element in the universe by mass. It constitutes about 2% of the Earth's crust by mass, and it is the third most abundant element dissolved in seawater. Magnesium ion is essential to all living cells, and is the 11th most abundant element by mass in the human body. 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 aluminium-magnesium alloys, sometimes called "magnalium" or "magnelium". Magnesium is priced at around $4 per kilogram.
Magnesium has three stable
26Mg has found application in
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.
Elemental magnesium is a fairly strong, silvery-white, light-weight metal (two thirds the density of aluminium). It tarnishes slightly 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 unnoticeably begin to form on the surface of the metal, though if powdered it will react much more rapidly. Magnesium also reacts with hydrochloric acid 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).
Magnesium, when it burns in air, produces a brilliant white light (images of burning magnesium). 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.
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 "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.
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. See manganese for this history.
Magnesium is the eighth most abundant element in the earth's crust. It is found in large deposits of magnesite, dolomite, and other minerals, and in mineral waters, where magnesium ion is soluble. 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 hydrated magnesium sulphate, MgSO4.
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. Davy's first suggestion for a name was magnium, but the name magnesium is now used.
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:
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.[1] 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).
Sea water frequently contains the Mg2+ cation, and to extract the magnesium, calcium carbonate is added to sea water to form magnesium carbonate precipitate.
MgCl2 + CaCO3 → MgCO3 + CaCl2
Magnesium carbonate is insoluble in water so it can be filtered out, and reacted with hydrochloric acid to obtain concentrated magnesium chloride.
MgCO3 + 2HCl → MgCl2 + CO2 + H2O
From magnesium chloride, electrolysis produces magnesium.
Magnesium ions are essential to the basic nucleic acid chemistry of life, and thus are 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 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 crushed dolomitic limestone to the soil.
Magnesium is a vital component of a healthy human diet and deficiency has been implicated in a number of human diseases. Magnesium is readily available in many common foods but studies indicate that many Americans are magnesium deficient. Supplemental magnesium is readily available and it is also difficult to overdose on magnesium. General failure of the kidneys may also lead to magnesium imbalance.
Magnesium is the third most commonly used structural metal, following steel and aluminium.
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 aluminium with these aluminium-magnesium alloys being used mainly for beverage cans.
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". 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 aluminium 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.[2] New alloy development and lower costs, which are becoming competitive to aluminium, will further the number of automotive applications.
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 include:
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, and if burning it, these should include a heavy U.V. filter, similar to welding eye protection. The bright white light (including ultraviolet) produced by burning magnesium can permanently damage the retinas of the eyes, similar to welding arc burns.[3]
Water should not be used to extinguish magnesium fires, because it can produce hydrogen which will feed the fire, according to the reaction:[4]
