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Manganese

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                25               chromium ← manganese → iron
                 -
                ↑
                Mn
                ↓
                Tc

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                    Name, Symbol, Number manganese, Mn, 25
                                         Chemical series transition metals
                                              Group, Period, Block 7, 4, d
                                               Appearance silvery metallic
                                           Atomic mass 54.938045 (5) g/mol
                                     Electron configuration [Ar] 3d^5 4s^2
                                           Electrons per shell 2, 8, 13, 2
                                                       Physical properties
                                                               Phase solid
                                       Density (near r.t.) 7.21 g·cm^−3
                                    Liquid density at m.p. 5.95 g·cm^−3
                                                     Melting point 1519  K
                                                    (1246 ° C, 2275 ° F)
                                                      Boiling point 2334 K
                                                    (2061 ° C, 3742 ° F)
                                         Heat of fusion 12.91 kJ·mol^−1
                                     Heat of vaporization 221 kJ·mol^−1
                          Heat capacity (25 °C) 26.32 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                      P/Pa   1    10  100  1 k  10 k 100 k
                                     at T/K 1228 1347 1493 1691 1955 2333

                                                         Atomic properties
                                     Crystal structure cubic body centered
                                            Oxidation states 7, 6, 4, 2, 3
                                                   (strongly acidic oxide)
                                    Electronegativity 1.55 (Pauling scale)
                                                       Ionization energies
                                           ( more) 1st: 717.3 kJ·mol^−1
                                                  2nd: 1509.0 kJ·mol^−1
                                                    3rd: 3248 kJ·mol^−1
                                                      Atomic radius 140 pm
                                              Atomic radius (calc.) 161 pm
                                                    Covalent radius 139 pm
                                                             Miscellaneous
                                             Magnetic ordering nonmagnetic
                              Electrical resistivity (20 °C) 1.44 µΩ·m
                       Thermal conductivity (300 K) 7.81 W·m^−1·K^−1
                       Thermal expansion (25 °C) 21.7 µm·m^−1·K^−1
                               Speed of sound (thin rod) (20 °C) 5150 m/s
                                                   Young's modulus 198 GPa
                                                      Bulk modulus 120 GPa
                                                         Mohs hardness 6.0
                                                  Brinell hardness 196 MPa
                                             CAS registry number 7439-96-5
                                                         Selected isotopes

                CAPTION: Main article: Isotopes of manganese

                            iso   NA   half-life   DM    DE ( MeV)    DP
                           ^52Mn syn  5.591 d      ε   -             ^52Cr
                                                   β^+ 0.575         ^52Cr
                                                   γ   0.7, 0.9, 1.4 -
                           ^53Mn syn  3.74 ×10^6 y ε   -             ^53Cr
                           ^54Mn syn  312.3 d      ε   -             ^54Cr
                                                   γ   0.834         -
                           ^55Mn 100% Mn is stable with 30 neutrons

                                                                References

   Manganese ( IPA: /ˈmaŋgəniːz/, /ˈmæŋgəniːz/) is a chemical element in
   the periodic table that has the symbol Mn and atomic number 25.

Notable characteristics

   Manganese
   Enlarge
   Manganese

   Manganese is a gray-white metal, resembling iron. It is a hard metal
   and is very brittle, fusible with difficulty, but easily oxidized.
   Manganese metal is ferromagnetic only after special treatment.

   The most common oxidation states of manganese are +2, +3, +4, +6 and
   +7, though oxidation states from +1 to +7 are observed. Mn^2+ often
   competes with Mg^2+ in biological systems, and manganese compounds
   where manganese is in oxidation state +7 are powerful oxidizing agents.

Applications

   Manganite, a manganese oxide
   Enlarge
   Manganite, a manganese oxide

   Manganese is essential to iron and steel production by virtue of its
   sulfur-fixing, deoxidizing, and alloying properties. Steelmaking,
   including its ironmaking component, has accounted for most manganese
   demand, presently in the range of 85% to 90% of the total demand. Among
   a variety of other uses, manganese is a key component of low-cost
   stainless steel formulations and certain widely used aluminium alloys.
   It is also added to gasoline in order to reduce engine knocking.
   Manganese(IV) oxide (manganese dioxide) is used in the original type of
   dry cell battery. Manganese dioxide is also used as a reagent in
   organic chemistry for the oxidation of benzylic alcohols (i.e. adjacent
   to an aromatic ring). Manganese is used to decolorize glass (removing
   the greenish tinge that presence of iron produces) and, in higher
   concentration, make violet-colored glass. Manganese oxide is a brown
   pigment that can be used to make paint and is a component of natural
   umber. Potassium permanganate is a potent oxidizer and used in
   chemistry and in medicine as a disinfectant. Manganese phosphating is
   used for rust and corrosion preventation on steel. It is very
   occasionally used in coins; the only United States coins to use
   manganese were the "Wartime" nickel from 1942–1945, and the Sacagawea
   Dollar (2000–present).

   The overall level and nature of manganese use in the United States is
   expected to remain about the same in the near term. No practical
   technologies exist for replacing manganese with other materials or for
   using domestic deposits or other accumulations to reduce the complete
   dependence of the United States on other countries for manganese ore.

   Substitutes: Manganese has no satisfactory substitute in its major
   applications. In minor applications, (e.g., manganese phosphating),
   zinc and sometimes vanadium are viable substitutes.

History

   Manganese (apparently from Latin magnes, meaning "magnet") was in use
   in prehistoric times; paints that were pigmented with manganese dioxide
   can be traced back 17,000 years. The Egyptians and Romans used
   manganese compounds in glass-making, to either remove color from glass
   or add colour to it. Manganese can be found in the iron ores used by
   the Spartans. Some speculate that the exceptional hardness of Spartan
   steels derives from the inadvertent production of an iron-manganese
   alloy.

   In the 17th century, German chemist Johann Glauber first produced
   permanganate, a useful laboratory reagent (although some people believe
   that it was discovered by Ignites Kaim in 1770). By the mid 18th
   century, manganese dioxide was in use in the manufacture of chlorine.
   The Swedish chemist Scheele was the first to recognize that manganese
   was an element, and his colleague, Johan Gottlieb Gahn, isolated the
   pure element in 1774 by reduction of the dioxide with carbon. Around
   the beginning of the 19th century, scientists began exploring the use
   of manganese in steelmaking, with patents being granted for its use at
   the time. In 1816, it was noted that adding manganese to iron made it
   harder, without making it any more brittle. In 1837, British academic
   James Couper noted an association between heavy exposure to manganese
   in mines with a form of Parkinson's Disease. In 1912, manganese
   phosphating electrochemical conversion coatings for protecting firearms
   against rust and corrosion were patented in the United States, and have
   seen widespread use ever since.

Biological role

   Manganese is an essential trace nutrient in all forms of life.

   The classes of enzymes that have manganese cofactors are very broad and
   include such classes as oxidoreductases, transferases, hydrolases,
   lyases, isomerases, ligases, lectins, and integrins. The best known
   manganese-containing polypeptides may be arginase, Mn-containing
   superoxide dismutase, and the diphtheria toxin.

Occurrence

   Manganese ore
   Enlarge
   Manganese ore

   Manganese occurs principally as pyrolusite ( MnO[2]), and to a lesser
   extent as rhodochrosite ( MnCO[3]). Land-based resources are large but
   irregularly distributed; those of the United States are very low grade
   and have potentially high extraction costs. Over 80% of the known world
   manganese resources are found in South Africa and Ukraine. Other
   important manganese deposits are in China, Australia, Brazil, Gabon,
   India, and Mexico.

   US Import Sources (1998-2001): Manganese ore: Gabon, 70%; South Africa,
   10%; Australia, 9%; Mexico, 5%; and other, 6%. Ferromanganese: South
   Africa, 47%; France, 22%; Mexico, 8%; Australia, 8%; and other, 15%.
   Manganese contained in all manganese imports: South Africa, 31%; Gabon,
   21%; Australia, 13%; Mexico, 8%; and other, 27%.

   Manganese is mined in Burkina Faso and Gabon.

   Vast quantities of manganese exist in manganese nodules on the ocean
   floor. Attempts to find economically viable methods of harvesting
   manganese nodules were abandoned in the 1970s.

Compounds

   Potassium permanganate, also called Condy's crystals, is a commonly
   used laboratory reagent because of its oxidizing properties and finds
   use as a topical medicine (for example, in the treatment of fish
   diseases).

   Manganese(IV) oxide (manganese dioxide) is used in dry cells, and can
   be used to decolorize glass that is polluted by trace amounts of iron.
   Manganese compounds can color glass an amethyst color, and are
   responsible for the colour of true amethyst. Manganese dioxide is also
   used in the manufacture of oxygen and chlorine, and in drying black
   paints.

   The most stable oxidation state for manganese is +2, and many
   manganese(II) compounds are known, such as manganese(II) sulfate
   (MnSO[4]) and manganese(II) chloride (MnCl[2]). This oxidation state is
   also seen in the mineral rhodochrosite, ( manganese(II) carbonate). The
   +3 oxidation state is also known, in compounds such as manganese(III)
   acetate, but these are quite powerful oxidizing agents.

   Methylcyclopentadienyl manganese tricarbonyl is used as an additive in
   unleaded gasoline.

Isotopes

   Naturally occurring manganese is composed of 1 stable isotope; ^55Mn.
   18 radioisotopes have been characterized with the most stable being
   ^53Mn with a half-life of 3.7 million years, ^54Mn with a half-life of
   312.3 days, and ^52Mn with a half-life of 5.591 days. All of the
   remaining radioactive isotopes have half lives that are less than 3
   hours and the majority of these have half lives that are less than 1
   minute. This element also has 3 meta states.

   Manganese is part of the iron group of elements which are thought to be
   synthesized in large stars shortly before supernova explosion. ^53Mn
   decays to ^53Cr with a half-life of 3.7 million years. Because of its
   relatively short half-life, ^53Mn is an extinct radionuclide. Manganese
   isotopic contents are typically combined with chromium isotopic
   contents and have found application in isotope geology and radiometric
   dating. Mn-Cr isotopic ratios reinforce the evidence from ^26Al and
   ^107Pd for the early history of the solar system. Variations in
   ^53Cr/^52Cr and Mn/Cr ratios from several meteorites indicate an
   initial ^53Mn/^55Mn ratio that suggests Mn-Cr isotopic systematics must
   result from in-situ decay of ^53Mn in differentiated planetary bodies.
   Hence ^53Mn provides additional evidence for nucleosynthetic processes
   immediately before coalescence of the solar system.

   The isotopes of manganese range in atomic weight from 46 amu (^46Mn) to
   65 amu (^65Mn). The primary decay mode before the most abundant stable
   isotope, ^55Mn, is electron capture and the primary mode after is beta
   decay.

Precautions

   Manganese compounds are less toxic than those of other widespread
   metals such as iron, nickel and copper compounds. However manganese is
   toxic in excess. Exposure to manganese dusts and fumes should not
   exceed the ceiling value of 5 mg/m^3 for even short periods because of
   its toxicity level.

   Acidic permanganate solutions will oxidize any organic material they
   come into contact with. The oxidation process can generate enough heat
   to ignite some organic substances.

   In 2005, a study suggested a possible link between manganese inhalation
   and central nervous system toxicity in rats. It is hypothesized that
   long-term exposure to the naturally-occurring manganese in shower water
   puts up to 8.7 million Americans at risk.

   A form of Parkinson's Disease-type neurodegeneration called "
   Manganism" has been linked to manganese exposure amongst miners and
   smelters since the early 19th Century. Allegations of
   inhalation-induced manganism have been made regarding the welding
   industry. Manganese exposure is regulated by OSHA.

   Retrieved from " http://en.wikipedia.org/wiki/Manganese"
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   with only minor checks and changes (see www.wikipedia.org for details
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