Molybdenum, a hard, silvery, metallic element. It is insoluble in most acids, and does not react with air at ordinary temperatures. Molybdenum is never found free in nature. Its main source is the mineral molybdenite. The leading producers of molybdenum are the United States, China, Chile, and Canada. Most of it is used in making steel, primarily to increase hardness and strength. Molybdenum is also used in lubricants, pigments, and high-temperature alloys. Molybdenum was discovered by Karl Wilhelm Scheele of Sweden in 1778.

Symbol: Mo. Atomic number: 42. Atomic weight: 95.94. Specific gravity: 10.2. Melting point: 4,743 F. (2,617 C). Boiling point: 8,334 F. (4,612 C). Molybdenum has seven natural isotopes. It belongs to Group VIB of the Periodic Table and may have a valence of + 2, 3, 4, 5, or 6.