MANGANESE (Mn)

 

MANGANESE (Mn)Atomic Number:25Atomic Weight:54.9380Melting Point:1244 C (2271.2 F)Boiling Point:1962 C (3563.6 F)Oxidation States:+2,+3,+4,+7

A metallic element, Mn, atomic number 25, and atomic weight 54.9380 g/mole. Manganese is one of the transition elements of the first long period of the periodic table, falling between chromium and iron. The principal properties of manganese are given in the table. It is the twelfth most abundant element in the Earth's crust (approximately 0.1%) and occurs naturally in several forms, primarily as the silicate (MnSiO3) but also as the carbonate (MnCO3) and a variety of oxides, including pyrolusite (MnO2) and hausmannite (Mn3O4). Weathering of land deposits has led to large amounts of the oxide being washed out to sea, where they have aggregated into the so-called manganese nodules containing 15–30% Mn. Vast deposits, estimated at over 1012 metric tons, have been detected on the seabed, and a further 107 metric tons is deposited every year. The nodules also contain smaller amounts of the oxides of other metals such as iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu). The economic importance of the nodules as a source of these important metals is enormous.  See also: Hausmannite; Manganese nodules; Periodic table; Pyrolusite

Manganese is more electropositive than its near neighbors in the periodic table, and consequently more reactive. The bulk metal undergoes only surface oxidation when exposed to atmospheric oxygen, but finely divided metal is pyrophoric.

Manganese is a trace element essential to a variety of living systems, including bacteria, plants, and animals. In contrast to iron (Fe), its neighbor in the periodic table, the exact function of the manganese in many of these systems was determined only recently. The manganese superoxide dismutases have been isolated from bacteria, plants, and animals, and are relatively small enzymes with molecular weights of approximately 20,000. The function of the enzyme is believed to be protection of living tissue from the harmful effects of the superoxide ion (O2−), a radical formed from partial reduction of O2 in the cells of respiring (O2-utilizing) cells.

The most important biological role yet recognized for manganese is in the enzyme responsible for photosynthetic water oxidation to oxygen in plants and certain photosynthetic bacteria. This reaction represents the source of oxygen gas on the Earth and is therefore responsible for the development of the most common forms of life.

All steels contain some manganese, the major advantage being an increase in hardness, although it also serves as a scavenger of oxygen and sulfur impurities that would induce defects and consequent brittleness in the steel. Manganese even has some use in the electronics industry, where manganese dioxide, either natural or synthetic, is employed to produce manganese compounds possessing high electrical resistivity; among other applications, these are utilized as components in every television set.  See also: Electrolysis; Glass; Metal; Transition elements

Bibliography

  • F. A. Cotton et al., Advanced Inorganic Chemistry, 6th ed., Wiley-Interscience, 1999
  • Ali Fazeli = egeology.blogfa.com
  • N. N. Greenwood and A. Earnshaw, Chemistry of the Elements, 2d ed., 1997
  • Ali Fazeli = egeology.blogfa.com
  • A. G. Sykes (ed.), Advances in Inorganic Chemistry, vol. 49, 1999
  • Ali Fazeli = egeology.blogfa.com

 

Additional Readings

  •  WebElements periodic table
  • Ali Fazeli = egeology.blogfa.com