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  Wikipedia: Manganese

Wikipedia: Manganese
Manganese
From Wikipedia, the free encyclopedia.

Chromium - Manganese - Iron
Mn
Tc  
 
 
General
Name, Symbol, NumberManganese, Mn, 25
Chemical series Transition metals
Group, Period, Block7 , 4 , d
Density, Hardness 7470 kg/m3, 6.0
Appearance silvery metallic
Atomic properties
Atomic weight 54.938049 amu
Atomic radius (calc.) 140 (161) pm
Covalent radius 139 pm
van der Waals radius n/a pm
Electron configuration [Ar]3d3d54s2
e- 's per energy level2, 8,13,2
Oxidation states (Oxide) 7,6,4,2,3 (strong acid)
Crystal structure Cubic body centered
Physical properties
State of matter solid (usually nonmagnetic)
Melting point 1517 K (2271 F)
Boiling point 2235 K (3564 F)
Molar volume 7.35 ×1010-6 m3/mol
Heat of vaporization 226 kJ/mol
Heat of fusion 12.05 kJ/mol
Vapor pressure 121 Pa at 1517 K
Velocity of sound 5150 m/s at 293.15 K
Miscellaneous
Electronegativity 1.55 (Pauling scale)
Specific heat capacity 480 J/(kg*K)
Electrical conductivity 0.695 106/m ohm
Thermal conductivity 7.82 W/(m*K)
1st ionization potential 717.3 kJ/mol
2nd ionization potential 1509 kJ/mol
3rd ionization potential 3248 kJ/mol
4th ionization potential 4940 kJ/mol
5th ionization potential 6990 kJ/mol
6th ionization potential 9220 kJ/mol
7th ionization potential 11500 kJ/mol
Most stable isotopes
isoNAhalf-life DMDE MeVDP
52Mn{syn.}5.591 days &epsilon4.71252Cr
53Mn{syn.}3.74 million yearsε0.59753Cr
54Mn{syn.}312.3 daysε1.37754Cr
54Mn{syn.}312.3 daysβ-0.69754Fe
55Mn100%Mn is stable with 30 neutrons
SI units & STP are used except where noted.
Manganese is a chemical element in the periodic table that has the symbol Mn and atomic number 25.

Notable characteristics

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

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 domestic 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 aluminum alloys. Manganese oxide is used in the original type of dry cell battery. 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 foreign countries for manganese ore.

Substitutes: Manganese has no satisfactory substitute in its major applications.

History

Manganese 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 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, the German chemist Glauber first produced permanganate, a useful laboratory reagent. By the mid 18th century, manganese oxide 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, J. G. 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.

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

Land-based resources are large but irregularly distributed; those of the United States are very low grade and have potentially high extraction costs. South Africa and Ukraine account for more than 80% of the world's identified resources; South Africa accounts for more than 80% of the total exclusive of China and Ukraine.

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.

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 dioxide is used in dry cells, and can be used to decolorize glass that is colored green by trace amounts of iron. Manganese compounds can color glass an amethyst color, and is responsible for the color of true amethyst. Manganese dioxide is also used in the manufacture of oxygen and chlorine, and in drying black paints.

Isotopes

Naturally occurring manganese is composed of 1 stable isotope; 55-Mn. 18 radioisotopes have been characterized with the most stable being 53-Mn with a half-life of 3.7 million years, 54-Mn with a half-life of 312.3 days, and 52-Mn 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. Manganese-53 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. 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 (46-Mn) to 65 amu (65-Mn). The primary decay mode before the most abundant stable isotope, 55-Mn, is electron capture and the primary mode after is beta.

Precautions

Manganese in excess is toxic. Exposure to manganese dusts, fume, and compounds should not exceed the ceiling value of 5 mg/m3 for even short periods because of the element's toxicity level.

Acidic permanganate solutions will destroy any organic material they come in contact with, and can set them on fire.

Reference

External Links


  

From Wikipedia, the free encyclopedia. 
Modified by Geona