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Magnesium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                12             sodium ← magnesium → aluminium
                Be
                ↑
                Mg
                ↓
                Ca

                                  Periodic Table - Extended 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] 3s^2
                                               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

   CAPTION: 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
                                                         Selected isotopes

                CAPTION: 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 ( IPA: /magˈniːziəm, -ʒəm/) 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. 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 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 it early history.

   It is conventional to plot ^26Mg/^24Mg against an Al/Mg ratio. In an
   isochron dating plot, the Al/Mg ratio plotted is^27Al/^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 impermeable and hard to
   remove. Like its lower periodic table group neighbour 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 of little practical import, 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 Mg^2+. 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 Scotland 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.

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 sex, weight and size, is
   300-400 mg/day. Inadequate magnesium intake frequently causes muscle
   spasms, and has been associated with cardiovascular disease, diabetes,
   high blood pressure, anxiety disorders and osteoporosis. Acute
   deficiency (see hypomagnesemia) 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
   when given parenterally) are used therapeutically for a number of
   medical conditions, especially the hypertension of eclampsia. See epsom
   salts for a list of conditions which have been treated with
   supplemental magnesium ion. 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.

Applications

As the metal

   Magnesium is the third most commonly used structural metal, following
   steel and aluminium.
   Products made of magnesium: firestarter and shavings, sharpener,
   magnesium band
   Enlarge
   Products made of magnesium: firestarter and shavings, sharpener,
   magnesium band

   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 to 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 completely 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.
   However, there is renewed interest in magnesium engine blocks, as
   featured in the 2006 BMW 325i and 330i models. The award-winning 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 . New alloy development and
   lower costs, which are becoming competitive to aluminium, will further
   the number of automotive applications.

   In December 2005, for the first time on record, the automotive grade
   magnesium alloy price per cm³ dropped below the A380 aluminium alloy
   price per cm³.

   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, laptops, cameras, etc.
   housings 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. However, 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 in aerospace
   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:
     * Removal of sulfur from iron and steel.
     * Photoengraved plates in the printing industry.
     * Combined in alloys, this metal is essential for airplane and
       missile construction.
     * When used as an alloying agent, this metal improves the mechanical,
       fabrication and welding characteristics of aluminium.
     * Additive agent for conventional propellants and used in producing
       nodular graphite in cast iron.
     * Reducing agent for the production of pure uranium and other metals
       from their salts.
     * Magnesium turnings or ribbon are used to prepare Grignard reagents,
       which are useful in organic synthesis
     * Easily reacting with water, it can serve as a desiccant
     * Magnesium is also flammable, burning at a temperature of
       approximately 2500 K (2200 °C, 4000 °F).
     * The autoignition temperature of magnesium is approximately 744 K
       (473 °C, 883 °F).
     * The extremely high temperature at which magnesium burns makes it a
       handy tool for starting emergency fires during outdoor recreation.
     * Other uses include flashlight photography, flares, pyrotechnics,
       sparklers, and incendiary bombs.

In magnesium compounds

     * Magnesium's hydroxide is used in milk of magnesia, its chloride and
       citrate used as oral magnesium supplements, and its sulfate ( Epsom
       salts) for various purposes in medicine, and elsewhere.
     * Dead-burned magnesite is used for refractory purposes such as brick
       and liners in furnaces and converters.
     * Magnesium carbonate (Mg CO[3]) powder is also used by athletes,
       such as gymnasts and weightlifters, to improve the grip on objects
       – the apparatus or lifting bar.
     * Magnesium stearate is a slightly flammable white powder with
       lubricative properties. In pharmaceutical technology it is used in
       the manufacturing 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).
     * The magnesium ion is necessary for all life (see magnesium in
       biological systems), so magnesium salts are an additive for foods,
       fertilizers (Mg is a component of chlorophyll), and culture media.

Precautions

   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)] + 2 H[2]O [(g)] → Mg(OH)[2] [(aq)] + H[2] [(g)]
          or in words:
          Magnesium [(solid)] + steam → Magnesium hydroxide [( aqueous)] +
          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.

   Retrieved from " http://en.wikipedia.org/wiki/Magnesium"
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