molybdenum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A hard, silvery-white metallic element used to toughen alloy steels and soften tungsten alloy. An essential trace element in plant nutrition, it is used in fertilizers, dyes, enamels, and reagents. Atomic number 42; atomic weight 95.94; melting point 2,617°C; boiling point 4,612°C; specific gravity 10.22 (at 20°C); valence 2, 3, 4, 5, 6. See Table at element.

Century Dictionary and Cyclopedia

1. n. Chemical symbol, Mo; atomic weight, 95. 8. A metal of a silver-white color, but harder than silver, which fuses with difficulty, if at all, at the highest temperature of a wind-furnace. Its specific gravity is 8. 6. It is chemically related to chromium, tungsten, and uranium, and, like those metals, forms trioxids which are acid-forming and yield very characteristic salts. It is remarkable for the number of oxids and corresponding chlorids which it forms; but it is the least important economically of the group to which it belongs. The most abundant ore of molybdenum is the sulphuret (molybdenite), and the strong external resemblance of this mineral to graphite (Latin plumbago) led to the confusion of molybdena with that substance; moreover, external resemblance and certain chemical peculiarities caused still further difficulties of nomenclature, in which manganese, antimony, and even magnesia were involved. Thus, the peroxid of manganese was called by Linnæus molybdænum magnesii. These perplexities were not cleared up until toward the end of the last century; but finally, as the result of the labors of Scheele, Bergman, and Hjelm (1778-90), the metal molybdena, or molybdenum, as it is now more generally called, was isolated from its combinations. The ores of molybdenum are somewhat widely diffused, but rarely occur in any considerable quantity. The principal molybdeniferous minerals are molybdenite and wulfenite. There is also a molybdic ocher (the trioxid) and a carbonate (pateraite); various ores of iron also contain traces of this metal.

Wiktionary

1. n. A metallic chemical element (symbol Mo) with an atomic number of 42.

GNU Webster's 1913

1. n. (Chem.) A rare element of the chromium group, occurring in nature in the minerals molybdenite and wulfenite, and when reduced obtained as a hard, silver-white, difficulty fusible metal. Symbol Mo. Atomic number 42. Atomic weight 95.94.

WordNet 3.0

1. n. a polyvalent metallic element that resembles chromium and tungsten in its properties; used to strengthen and harden steel