The nature of the manganese

Dec 12 08:26 2012 David Yvon Print This Article

According to metal powder supplier, manganese is a metallic element, it is widespread in nature in compound form, the average content of manganese in earthcrust is about 0.1% (by  mass), in the Periodic Table, manganese is a transition element, adjacent to chromium, iron, its chemical activity is weaker than chromium, stronger than iron. 

The physical properties of the manganese,Guest Posting manganese is a cubic crystal, has ±, ², ³ and ´ four kinds allotropic body, in ambient temperature, the ± manganese is the most stable. Mechanical properties of manganese is hard and brittle, Mohs hardness is 5 to 6, the dense block manganese metal surface is silver-white, powdery is gray. The relative atomic weight of manganese is 54.9380 ± 1. Atomic volume is 7.39cm3/mol. The density of manganese atomic radius and at room temperature are slightly different with the different polymorphs, at room temperature, the atomic radius of manganese, density, are related to the polymorph.

Manganese is a reactive metal, susceptible to be oxidized. Manganese powderis easy to burn in air, but large massive metallic manganese is uneasy to be oxidized in the air erosion at ambient temperature, this is because the manganese metal surface in the air easy to generate a layer of oxide film, play a protective role on the inner metallic manganese. In water, it is easy to generate hydroxide film, and can further prevent the manganese on the replacement of the hydrogen in the water molecules. Due to the electrons in the outermost layer and the second outer (3d4s) can become a valence electron, so that manganese is an element of the price change. Manganese oxidation state have +2, +3, +4, +6 and +7. Valence of changes lead to changes in the ionic nature, such as the radius of the manganese ions smaller with a valence higher, ion potential and electrically negative increased with the valence increases correspondingly, the pH of their oxides with increased valence by alkaline to acidic changes. Homologous acid-base properties of oxide and hydrate of manganese is the most typical in the transition elements. It manifested that with the oxidation state of manganese, alkaline gradually weakened, acidic gradually increased.

Covalent radius of manganese is 117pm, the same as the covalent radius of the iron and copper; similar with the covalent radius of the chrome, diamond, nickel. Manganese belonging to the fourth period of the transition elements, compared with Sc, Ti, V, Cr, Fe, Co, Ni, especially compared with adjacent Cr and Fe, Mn has some special physical and chemical properties. These characteristics are with great significance for understanding the geochemical characteristics of manganese. The atomic radius of the transition elements in the fourth cycle, the general trend from Sc to Ni with the atomic number increases sequentially reduced, and only manganese is an exception. Its atomic radius is 136.6pm (³-Mn), larger than Cr (124.9pm) and Fe (124.1pm), undermining the law of diminishing. The fourth period transition in the oxidation state of the element, only the manganese has the highest +7 oxidation state. Transition elements before manganese (Sc of Cr) highest oxidation state is gradually increased from +3 to +6; transition elements after manganese (Fe to Ni) the highest oxidation state is gradually reduced from +6 to +3. The oxidation state of the transition elements before manganese increases is related to the increase number of valence electrons in the 3d orbitals. When the number of electrons in the 3d orbitals up to more than 5 (from Cr to Ni) 3d orbit gradually moving towards stability and high oxidation state gradually unstable, showing strong oxidizing gradually reduce the oxidation state of the transition elements manganese. In the fourth period transition element, manganese has the lowest melting point and boiling point. From Sc to of Cr, the melting point is 1539 ~ 1890, boiling point is 2483 to 3380; from Fe to Ni, the melting point is 1453 to 1535, the boiling point is 2732 to 3000 and manganese melting point is 1260, boiling point is 2077 its melting heat and heat of vaporization is also low. The standard electrode potential of the transition elements of the fourth cycle, substantially from Sc to Ni increases gradually. And their metallic weakened is consistent. But only manganese standard electrode potential is lower than chromium, undermining the law of this increment. Thus, manganese in the fourth cycle transition elements, has its unique physical and chemical properties.

Source:http://www.mhcmp.com

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