Tungsten (also called wolfram)[14][15] is a chemical element; it has symbolW and atomic number 74. It is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a distinct element in 1781 and first isolated as a metal in 1783. Its important ores include scheelite and wolframite, the latter lending the element its alternative name.
The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all known elements, melting at 3,422 °C (6,192 °F; 3,695 K). It also has the highest boiling point, at 5,930 °C (10,706 °F; 6,203 K).[16] Its density is 19.254 g/cm3,[4] comparable with that of uranium and gold, and much higher (about 1.7 times) than that of lead.[17] Polycrystalline tungsten is an intrinsically brittle[18][19][20] and hard material (under standard conditions, when uncombined), making it difficult to work into metal. However, pure single-crystalline tungsten is more ductile and can be cut with a hard-steel hacksaw.[21]
Tungsten is the only metal in the third transition series that is known to occur in biomolecules, being found in a few species of bacteria and archaea. However, tungsten interferes with molybdenum and copper metabolism and is somewhat toxic to most forms of animal life.[24][25]
^ abcdArblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN978-1-62708-155-9.
^W(−4) is known in W(CO)4−4; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8). doi:10.1021/ic052110i.
^W(0) is known in W(CO)6; see John E. Ellis (2006). "Adventures with Substances Containing Metals in Negative Oxidation States". Inorganic Chemistry. 45 (8). doi:10.1021/ic052110i.
^Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. p. E110. ISBN978-0-8493-0464-4.
^Daintith, John (2005). Facts on File Dictionary of Chemistry (4th ed.). New York: Checkmark Books. ISBN978-0-8160-5649-1.
^Lassner, Erik; Schubert, Wolf-Dieter (1999). "low temperature brittleness". Tungsten: properties, chemistry, technology of the element, alloys, and chemical compounds. Springer. pp. 20–21. ISBN978-0-306-45053-2.
^Cite error: The named reference :1 was invoked but never defined (see the help page).
^McMaster, J. & Enemark, John H. (1998). "The active sites of molybdenum- and tungsten-containing enzymes". Current Opinion in Chemical Biology. 2 (2): 201–207. doi:10.1016/S1367-5931(98)80061-6. PMID9667924.