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25 chromiummanganeseiron


Name, Symbol, Number manganese, Mn, 25
Chemical series transition metals
Group, Period, Block 74, d
Appearance silvery metallic
Standard atomic weight 54.938045(5) g·mol−1
Electron configuration [Ar] 4s2 3d5
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
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 A12
Oxidation states 7, 6, 4, 2, 3
(oxides: acidic, basic or amphoteric
depending on the oxidation state)
Electronegativity 1.55 (Pauling scale)
Ionization energies
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
Magnetic ordering paramagnetic
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
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 ×106 y ε - 53Cr
54Mn syn 312.3 d ε - 54Cr
γ 0.834 -
55Mn 100% Mn is stable with 30 neutrons
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Manganese (IPA: /ˈmæŋgəniːz/) is a chemical element that has the symbol Mn and atomic number 25. It is found as the free element in nature (often in combination with iron), and in many minerals. The free element is a metal with important industrial metal alloy uses. Manganese ions are variously colored, and are used industrially as pigments and as oxidation chemicals. Manganese (II) ions function as cofactors for a number of enzymes and the element is thus a required trace mineral for all known living organisms.


[edit] Notable chemical characteristics


Manganese is a grey-white metal, resembling iron. It is a hard metal and is very brittle, fusible with difficulty, but easily oxidized. Manganese metal and its common ions are paramagnetic. This means that, while manganese metal does not form a permanent magnet, it does exhibit strong magnetic properties in the presence of an external magnetic field.

The most common oxidation states of manganese are +2, +3, +4, +6 and +7, though oxidation states from +1 to +7 are observed. Mn2+ often competes with Mg2+ in biological systems, and manganese compounds where manganese is in oxidation state +7 are powerful oxidizing agents.

[edit] Applications

[edit] The metal

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.

The metal is very occasionally used in coins; the only United States coins to use manganese were the "Wartime" nickel from 1942–1945, and, since 2000, dollar coins. The EU uses manganese in 1 and 2 Euro coins due to greater and cheaper availability.

[edit] Compounds

Some manganese compounds have been added to gasoline to boost octane rating and reduce engine knocking. 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 an amethyst-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.

Manganese(IV) oxide (manganese dioxide) was used in the original type of dry cell battery, and is the black material found when opening carbon-zinc type flashlight cells. The same material also functions in newer alkaline batteries (usually battery cells), which use the same basic reaction but a different electrolyte.

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, which are related to metallurgical alloy use. In minor applications, (e.g., manganese phosphating), zinc and sometimes vanadium are viable substitutes. In disposable battery manufacture, standard and alkaline cells using manganese will probably eventually be mostly replaced with lithium battery technology.

[edit] History

The origin of the name manganese is complex. In ancient times, two black minerals from Magnesia in what is now modern Greece were both called magnes, but were thought to differ in gender. The male magnes attracted iron, and was the iron ore we now know as loadstone or magnetite, and which probably gave us the term magnet. The female magnes ore did not attract iron, but was used to decolorize glass. This feminine magnes was later called magnesia, known now in modern times as pyrolusite or manganese dioxide. This mineral is never magnetic (although manganese itself is paramagnetic). In the 16th century, it was called manganesum by glassmakers, possibly as a corruption of two words since alchemists and glassmakers eventually had to differentiate a magnesia negra (the black ore) from magnesia alba (a white ore, also from Magnesia, also useful in glassmaking). Mercati called magnesia negra Manganesa, and finally the metal isolated from it became known as manganese (German: Mangan). The name magnesia eventually was then used to refer only to the white magnesia alba (magnesium oxide), which provided the name magnesium for that free element, when it was eventually isolated, much later. [1]

Manganese compounds were 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 color 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 (which it produces when mixed with hydrochloric acid, or commercially with a mixture of dilute sulfuric acid and sodium chloride). 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.

In the 20th century, manganese dioxide has seen wide commercial use as the chief cathodic material for commercial disposable dry cells and dry batteries of both the standard (carbon-zinc) and alkaline type.

[edit] 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, the diphtheria toxin, and Mn-containing superoxide dismutase (Mn-SOD), which is the enzyme typically present in eukaryotic mitochondria, and also in many bacteria (this fact is in keeping with the bacterial-origin theory of mitochondria). The Mn-SOD enzyme is probably one of the most ancient, for nearly all organisms living in the presence of oxygen use it to deal with the toxic effects of superoxide, formed from by the 1-electron reduction of dioxygen. Exceptions include a few kinds of bacteria such as Lactobacillus plantarum and related lactobacilli, which use a different non-enzymatic mechanism, involving manganese (Mn2+) ions complexed with polyphosphate directly for this task, indicating how this function possibly evolved in aerobic life.

[edit] Occurrence

Manganese ore
Manganese ore

Manganese occurs principally as pyrolusite (MnO2), and to a lesser extent as rhodochrosite (MnCO3). 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.

See also manganese minerals.

[edit] 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 color 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 (MnSO4) and manganese(II) chloride (MnCl2). 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.

See also manganese compounds.

[edit] Isotopes

Template:Isotopes of manganese 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 u (46Mn) to 65 u (65Mn). The primary decay mode before the most abundant stable isotope, 55Mn, is electron capture and the primary mode after is beta decay.

[edit] 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/m3 for even short periods because of its toxicity level. Manganese posses a particular risk for children due to its propensity to bind to CH-7 receptors. Manganese poisoning has been linked to impaired motor skills and cognitive disorders.

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.[1] 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.[2]

[edit] Manganese in popular culture

  • In the film Caddyshack, Carl the Groundskeeper (Bill Murray) refers to manganese as one of the things he is learning about in order to become the head greenskeeper. During a conversation in his shack with Ty Webb, Carl says, "Manganese—most people don't even know what that is."

[edit] See also

[edit] References

  1. ^
  2. ^

[edit] External links

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