Manganese

What is Manganese?

Manganese is a silvery metal. It is found on the periodic table with the transition metals, and resembles iron. It has the largest number of stable isotopes of any element. It was a component of pigments used by Stone Age people to draw cave paintings over 30,000 years ago. Today, it is used in alloys of iron and aluminum, in pigments, and in batteries. It is also essential to life.

Manganese’s Place in the Periodic Table

Manganese is a transition metal in period 4 and group 7. It can form compounds with oxygen, alkali, and alkali earth metals to form strong oxidizing agents. Like other transition metals, pure manganese reacts with air to form rust. Some forms of manganese are paramagnetic, which means that they are weakly attracted to magnets. Manganese was present in a black mineral from Magnesia, which is a region in Greece after which the element is named.

Atomic number: 25
Atomic Radius: 127 picometers
Atomic mass: 54.94
Symbol: Mn
Group: 7
Period: 4
Number of Protons: 25
Number of Electrons: 25
Number of Neutrons: ~30
Number of Isotopes: 2 natural isotopes

Properties of Manganese

Manganese is a silvery gray metal. It is stable at room temperature but reacts with air to form an oxidized layer on its surface (right). It is hard, brittle, and difficult to fuse. It has numerous oxidations states with varying stabilities. It can be extracted from ores using strong acid. Manganese conducts heat poorly and has high resistance to electric current. It is essential in most biological systems but its compounds can be very toxic.

Physical Properties

Manganese is solid at room temperature and has a density similar to zinc and iron. It melts at 1246°C. At that temperature, paper would spontaneously combust. It has a boiling point of 2061°C, which is close to cast iron, a carbon and iron alloy.

Melting Point: 1246°C.
Boiling Point: 2061°C.
Density of Solid Manganese: 21 g cm^-3
Phase at Room Temperature: solid

Chemical Properties

Manganese has 2 valence electrons. It has several oxidation states with varying stabilities The most common oxidation states of manganese are +2, +3, +4, +6, and +7. It forms many compounds that dissolve in water. Manganese(VII) and Manganese(III) compounds are very reactive and strong oxidizing agents. Manganese(III) compounds are unstable and can spontaneously decompose into two compounds, one with a higher oxidations state, and one with a lower oxidation state. Mn(II) compounds are the most stable, and include chlorides, carbonates, and oxides.

Oxidation states: -3, -2, -1, +1, +2, +3, +4, +5, +6, +7
Specific Heat: 0.48 J g^-1K^-1
Electronegativity: 1.55 (Pauling scale)
Heat of Fusion: 91 kj mol^-1
Heat of Vaporization: 221 kj mol^-1
Electron Configuration: [Ar] 3d⁵ 4s²

Isotopes

There is only one , Manganese-55, and one radioactive isotope, Manganese-53. Manganese-53 exist in trace amounts naturally. Manganese-53 has a half-life of about 4 million years. The universe is 1000 times older than that half-life, so most Mangese-53 is produced by the collision of iron with cosmic rays. Seventeen other radioactive isotopes have been identified in laboratories. These have half-lives ranging from a few nanoseconds to about a year. Manganese isotopes are used by geologists to date materials in the solar system, such as meteorites.

Alloys and Allotropes

Manganese is used in the production of iron and steel, which accounts for 85 to 90% of its demand. Steel that contains manganese has improved tensile strength, which means that it can resist greater bending forces without breaking. Manganese is also used in aluminum alloys to reduce its susceptibility to corrosion.

Compounds of Manganese

Potassium permanganate (KMnO₄) is a bright purple solid that is one of the strongest manganese oxidizing agents. It was one of the first chemicals used to dye fabrics. As a strong oxidizer, it is generally toxic, and has been used to treat skin infections. MnO₂can be used as a brown pigment. It is also used in alkaline batteries as an acceptor of electrons from zinc. Manganese fluorides have red luminescence and so can be used to produce red light in LEDs.

Interesting Facts about Manganese

Rhodochrosite, an ore of manganese, is the national stone of Argentina. It is also known as the Inca Rose, referring to its pink and red color.
The purple color of amethyst crystals is due to the presence of manganese.
High levels of manganese in drinking water can accumulate in the body and become toxic. This can have broad effects, including neurological disorders. Some scientists claim that children provided with water that had lower levels of manganese were associated with higher cognitive function and intelligence.
or molecules with an extra electron, making them unstable and reactive. In the body, free radicals can cause damage to DNA and lead to the development of cancer. Manganese is used by enzymes inside the cell to detoxify free radicals.

Occurrence and Abundance of Manganese

Manganese makes up 0.0008% of the universe. It is the 12^th most abundant element in the Earth’s crust and makes up about 0.11% of it. It exists mostly as oxides in the mineral deposits. Pyrolusite contains MnO₂ and rhodochrosite is a bright red, crystalline form of MnCO_3. The primary countries that have significant manganese deposits are China, Australia, South Africa, Gabon, and Brazil. There are also 500 billion tons of manganese in the form of golf ball-sized nodules on the ocean floor. Humans are composed of 0.00002% manganese, and it is recommended that adults consume around 2mg of manganese in their diet per day. Good sources of manganese include nuts, beans, grains, vegetables, and fruit. Or, you could just eat some dark chocolate.

Uses of Manganese

Most Notable Uses in General

Organic compounds that contain manganese are added to gasoline to improve octane ratings. It can be used to neutralize the green color in some forms of glass that is caused by contamination with iron. Over 230,000 tons of manganese are used each year to produce batteries. It is also part of alloys used to make coins. Metal cans also contain small amounts of manganese to prevent corrosion. Manganese oxide is a common component used in cement.

Most Notable Uses in Science

Manganese compounds are common in chemistry laboratories. Their strong oxidizing properties make them ideal in the synthesis of other chemical compounds. Manganese as a dietary supplement can be used to treat various medical conditions. Some people have natural manganese deficiencies. It can also promote bone and joint health and anemia.

Discovery of Manganese

Manganese dioxide has been used since the Stone Age as a pigment and in glassmaking. Chemists long knew that the material used for these applications contained an unknown element that they could not isolate. It was not until 1774 that Johan Gottlieb Gahn produced impure manganese metal by reducing it with carbon. However, given its long history, Gahn did not name the element.

Manganese in the Future

High purity manganese is now highly sought for the production of high performance lithium ion batteries that are being developed. It is believed that the enhancements in battery performance will triple the range of electric cars while maintaining the same weight.