MANGANESE Manganese Metal

Physical Properties

Atomic Number: 25
Mass Number: 54.9380
Electron Configuration: 1s²2s²2p⁶3s²3p⁶4s²3d⁵
Atomic Radius: 117 pm
Ionic Radius: 80 pm (Mn²⁺), 66 pm (Mn³⁺)
Melting Point: 1244^oC
Important Oxidation States: +2, +4, +7


Elemental Properties

Mangese is a hard metal, with a distinctive bronze color. Like cobalt, manganese is not particularly useful in elemental form; the primary use of manganese is in the manufacture of steel. The addition of manganese to steel increases the toughness and durability of steel. Manganese is also used to make alloys such as manganese bronze, which is an alloy of copper, zinc, and manganese. In elemental from, manganese is fairly reactive and will displace hydrogen from acids. Manganese exists in a wide range of oxidation states, including +7, +6, +5, +4, +2, and +2.

The +2 Oxidation State

The +2 oxidation state is very common for manganese and the most stable. Some example compounds include manganese sulfate and manganese chloride. In aqueous solution, the manganous ion exist as Mn(H₂O)₆²⁺ ion and has an octahedral geometry. Such compounds are usually pale pink in color. The paleness of the color is a consequence of the d⁵ electron configuration. Each orbital has a single electron and any electron transitions are spin-forbidden. In nonaqueous solvents the manganous ion forms numerous complexes that have a tetrahedral geometry. These tend to be much more intensely colored than the pale-pink octahedral ions. They are yellow-green in color, and some exhibit fluorescence. Rhodocrosite, MnCO₃, is a mineral which contains manganese in the +2 oxidation state.

Photos of the mineral rhodocrosite. Courtesy of R. Weller, Cochise College

The +4 Oxidation State

The +4 oxidation state is also a rather common oxidation state for manganese. Manganese dioxide, MnO₂ is comonly encountered compound that contains manganese in this oxidation state, This is a black insoluble solid that is generally consisdered to be ionic. It is commonly employed as an oxidizing agent in dry cells.

The +6 Oxidation State

The +6 oxidation state is not a common oxidation state for manganese. One example of manganese in this oxidation state is the manganate ion, MnO₄^2-. This ion is green in color and can be produced by treating the permangante ion, MnO₄^-, with a mild reducing agent such as dilute hydrogen peroxide.

The +7 Oxidation State

The highest oxidation state of manganese is the +7 state and corresponds to the complete removal of all the electrons from the 4s and 3d orbitals. A very good example of a compound in this oxidation state is the permanganate ion, MnO₄^-, This is also perhaps one of the most commonly encountered manganese compounds in the chemistry laboratory. As a solid, crystals of potassium permangante are so intensely colored they appear black. Solutions containing the permanganate ion are also intensely colored. The permanganate ion is a very good oxidizing agent and is commonly used in chemistry laboratory for this purpose. A common oxidation-reduction titration involves the addition of a potassium permanganate solution to a solution containing the oxalate ion or the ferrous ion. In this case the intense color of the permangante ion serves as a built-in indictaor, as even a small excess imparts a pink color to the solution bein titrated.

Solutions containing the MnO4- ion (left) and mn+2 ion (right).