Electron Orbital Assignments for Some Transition Elements

Molybdenum oxidises slowly in air at 350 C and readily at temperatures above 500 C, so that it cannot be used unprotected at such temperatures in air or other oxidising environments such as water vapour or carbon dioxide. The rate of oxidation depends on the temperature and the availability of the oxygen. It is rapid enough to cause ignition of very fine powder but not of the bulk metal. There is no intergranular penetration or diffusion of oxygen into the metal, and the surface film of oxide produced may be acceptable in some cases for components which are only required to operate for short periods at high temperatures. 

At high temperatures the metal will react slowly with certain gases. With carbon monoxide it produces a surface film of carbide, with nitrogen it produces a nitride film, and with hydrogen sulphide it reacts to form molybdenum disulphide. All of these films presumably interfere with the flow of gas to the metal surface, and in each case only a thin film of the product arises. Molybdenum is also very resistant to corrosive attack by mineral acids except for those such as nitric acid or chromic 

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Table 3.1 Electron Orbital Assignments for Some Transition Elements...

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