Manganese arsenides

MnAs MANGANESE ARSENIDE 1035 Mo02CI2 MOLYBDENUM DICHLORIDE DIOXIDE 1074 

Mn5SI3 5-MANGANESE 3-SILICON 1060 Na3As TRISODIUM ARSENIDE 1107 

On the basis of the expected charges on the monatomic ions, give the chemical formula of each of the following compounds (a) manganese(II) telluride (b) barium arsenide  

Rammelsbergite is readily oxidised by aerated waters, the oxidation proceeding much more rapidly than in the case of niccolite and other arsenide minerals 3 the oxidation is accelerated by the presence of iron pyrites, manganese dioxide or platinum black.4 

The increase in the overlap of the 3d shells observed in the series of compounds MnBi— MnSb — MnAs is due both to an increase of the radius of the electron shell and to a decrease of the distance between atoms in the [001] direction, which varies from df. j = 2.85 A in manganese arsenide to = 3.06 A in MnBi. The overlap of the 3d-shells of manganese atoms, 

The intermetallic compounds MnAs, MnSb, and MnBi crystallize with a nickel arsenide-type structure, and they have many features in common regarding their structure and nature of physical properties. At room temperature, all these compounds are ferromagnetic. The Curie point of manganese arsenide is 45°C of MnSb and MnBi it is 314 and 360°C, respectively. Their ferromagnetism is due to the uncompensated spins of the 3d electron shells of the manganese atoms, located at the crystal lattice points with the coordinates 0, 0, 0 and 0, 0, i. 

As can be seen in Fig. 3, the distinctive feature of the density distribution in MnAs, MnSb, and MnBi is the slower decrease of p in MnAs, when r is increased, than in MnSb and particularly MnBi. As a result, the maximum value of the electron density halfway between the atoms, i.e., where there is a possible overlap of the electron shells of the manganese atoms, is found in manganese arsenide. In absolute value, the electron density at r/dj. j = 0.5 is 0.01 electron/or 0.3% of the maximum value corresponding to r -= 0. 

With iron, cobalt and nickel, alcoholic solutions of the salts should be used, since with aqueous solutions the resulting arsenide is contaminated with free arsenic. Zinc and manganese arsenides are readily hydrolysed and cannot be obtained by the above method, but are prepared by combination of the elements. 

Cobalt is the thirtieth most abundant element on earth and comprises approximately 0.0025% of the earth s cmst (3). It occurs in mineral form as arsenides, sulfides, and oxides trace amounts are also found in other minerals of nickel and iron as substitute ions (4). Cobalt minerals are commonly associated with ores of nickel, iron, silver, bismuth, copper, manganese, antimony, and 2iac. Table 1 Hsts the principal cobalt minerals and some corresponding properties. A complete listing of cobalt minerals is given ia Reference 4. 

In Moroccan deposits, cobalt occurs with nickel in the forms of smaltite, skuttemdite, and safflorite. In Canadian deposits, cobalt occurs with silver and bismuth. Smaltite, cobaltite, erythrite, safflorite, linnaeite, and skuttemdite have been identified as occurring in these deposits. AustraUan deposits are associated with nickel, copper, manganese, silver, bismuth, chromium, and tungsten. In these reserves, cobalt occurs as sulfides, arsenides, and oxides. 

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