Manganese

Manganese is chemical element 25 on the periodic table. Its symbol is Mn. (Some people get it confused with magnesium, the symbol is Mg). Manganese is used a lot in steel to make it stronger. This is the main use for manganese metal. Manganese compounds, particularly manganese(IV) oxide, are used in alkaline cells and Leclanche cells. Manganese metal is also alloyed with aluminium.

Our bodies and plants need manganese to work right. If we do not get enough manganese, we can get sick. We get manganese from our food and vitamins also have some manganese to make sure that we get enough. It has 25 protons. Its mass number is 54.94.

Properties

Manganese is a silvery-gray metal and is part of the group known as the transition metals. It is similar to iron. It is hard to melt, but easy to oxidize. Manganese forms chemical compounds in several oxidation states: +2, +4, and +7 are the most common. Manganese compounds can be black, brown, pink, red, green, blue, and purple. Manganese(II) compounds are pink or light brown. They are unreactive. Manganese(II) chloride is a common example. Manganese(III) compounds are weak oxidizing agents. Manganese(IV) compounds are stronger oxidizing agents, but they are rarer. They are normally black in colour. Manganese(IV) oxide is an example.

Manganese(V) compounds are not stable and disproportionate easily. They are bright blue. They are very rare. Hypomanganates are the most common manganese(V) compounds. Manganese(VI) compounds are made in the process used to make permanganates. They disproportionate too. Manganates are weak reducing agents and moderate oxidizing agents. They are bright green.

Manganese(VII) compounds are purple-black and are powerful oxidizing agents. Permanganates contain the MnO4- ion. They are normally purple-black and strong oxidizing agents. Potassium permanganate is an example.

Isotopes 
Manganese that is found in nature is made up of one stable isotope, which is manganese-55. Manganese has many radioisotopes ranging from manganese-44 to manganese-69. The most stable radioisotope is manganese-53. It has a half-life of 3.7 million years.

Occurrence
The Earth's crust contains about 1000 ppm of manganese. It is the 12th most abundant element in the Earth's crust. Soil contains 7–9000 ppm of manganese. Seawater only contains 10 ppm of manganese. The atmosphere contains 0.01 µg/m3 of manganese. Manganese mainly occurs as pyrolusite, braunite, psilomelane.

Manganese is sometimes found alloyed with iron naturally. These rocks, called meteorites, came from space. Pyrolusite is one of the main sources of manganese. It also occurs as manganese carbonate. Some silicates have manganese in them. The derivation of Manganese may have come from either the Latin 'magnes', meaning magnet, or from the black magnesium oxide, 'magnesia nigra'.

Preparation
Manganese is normally made in an alloy with steel. This is made by mixing manganese ore and iron ore in a furnace and reducing it with carbon. This forms an alloy called ferromanganese. Pure manganese is made by reacting the manganese ore with sulfuric acid and electrolyzing it.

Our bodies and plants need manganese to work right. If we do not get enough manganese, we can get sick. We get manganese from our food and vitamins also have some manganese to make sure that we get enough.

Uses 
Manganese is used to make cheap stainless steel. Methylcyclopentadienyl manganese tricarbonyl is used as an additive in gasoline that does not have lead to reduce engine knocking.

Manganese(IV) oxide is used as a reagent in organic chemistry for the oxidation of benzylic alcohols. Manganese dioxide is also used in the manufacture of oxygen and chlorine. It is also used to dry black paints. Sometimes, it is used as a brown pigment for paint. It is a component of natural umber.

Manganese compounds have been used as pigments to color ceramics and glass. Tetravalent manganese is used as an activator in phosphors that glow red. Manganese oxide is also used in Portland cement mixtures.

Biological role 

There are lots of classes of enzymes that have manganese cofactors. They are oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases, lectins, and integrins. The reverse transcriptases of many retroviruses contain manganese.

Biological role in humans 
Manganese is an essential nutrient. It is found as a coenzyme in many biological processes. They include macronutrient metabolism, bone formation, and free radical immune system. It is a very important component in lots of proteins and enzymes. The human body contains about 12 mg of manganese. Manganese is found in the bones, liver, brain and kidneys. In the human brain, the manganese is bound to manganese metalloproteins.

Biological role in plants 
Manganese is also important in the photosynthetic oxygen evolution in the chloroplasts of plants. The oxygen-evolving complex is a part of photosystem II. The photosystem ll is found in the thylakoid membranes of chloroplasts. It is responsible for the photooxidation of water during the light reactions of photosynthesis. It has a metalloenzyme core that has four atoms of manganese.

Safety
Manganese dust can irritate lungs. Some manganese compounds cause toxicity when ingested. Manganese is less toxic than nickel or copper. Permanganates are the most toxic manganese compounds. When someone is exposed to manganese for a long time it can cause a problem with the nervous system.

Related pages
Manganese compounds
List of common elements

References

Other websites 

 National Pollutant Inventory - Manganese and compounds Fact Sheet 
 International Manganese Institute

Transition metals