Molybdenum
Molybdenum, symbol Mo, metallic element with chemical properties similar to those of chromium . Molybdenum is one of the transition elements of the periodic table (see Periodic Law). The atomic number of molybdenum is 42. Molybdenum was discovered in 1778 by the Swedish chemist Carl Wilhelm Scheele . It is a silvery white, tough, malleable metal. Molybdenum is dissolved by dilute nitric acid and aqua regia , and is attacked by fused alkalies; it is not attacked by air at ordinary temperatures, but at elevated temperatures it oxidizes to form molybdenum oxide. Molybdenum melts at about 2610° C (about 4730° F), boils at about 4640° C (about 8380° F), and has a specific gravity, or relative density, of 10.2. Molybdenum does not occur free in nature, but in the form of its ores, the most important of which are molybdenit e and wulfenite . It ranks 56th in order of abundance of the elements in the crust of the earth and is an important trace element in soils, where it contributes to the gr