Group 6 element


Group 6 element
Group → 6
↓ Period
4 Chromium crystal bar
24
Cr
5 Molybdenum crystal bar
42
Mo
6 Tungsten crystal bar
74
W
7 106
Sg

Legend
Transition metal
Primordial element
Synthetic

A Group 6 element is one in the series of elements in group 6 (IUPAC style) in the periodic table, which consists of the transition metals chromium (Cr), molybdenum (Mo), tungsten (W), and seaborgium (Sg).

Like other groups, the members of this family show patterns in its electron configuration, especially the outermost shells resulting in trends in chemical behavior:

Z Element No. of electrons/shell
24 chromium 2, 8, 13, 1
42 molybdenum 2, 8, 18, 13, 1
74 tungsten 2, 8, 18, 32, 12, 2
106 seaborgium 2, 8, 18, 32, 32, 12, 2

"Group 6" is the new IUPAC name for this group; the old style name was "group VIA" in the old European system or "group VIB" in the old US system. Group 6 must not be confused with the group with the old-style group names of either VIB (European system) or VIA (US system); that group is now called group 16.


Contents

History

The red colour of rubies is from a small amount of chromium(III).

Discoveries

The first reported use of chromium dates from the late 3rd century BC (by Qin Dynasty) in China: weapons from the artea were analyzed and found out to be coated with chromium, which allowed to prevent their corrosion.[1] Since then, chromium has not been reported up to July 26, 1761, when Johann Gottlob Lehmann found an orange-red mineral in the Beryozovskoye mines in the Ural Mountains of Russia, which he named "Siberian red lead," which was found out in less than 10 years to be a bright yellow pigment.[2] Though misidentified as a lead compound with selenium and iron components, the mineral was crocoite with a formula of PbCrO4.[2] Studying the mineral in 1797, Louis Nicolas Vauquelin produced chromium trioxide by mixing crocoite with hydrochloric acid metallic chromium by heating the oxide in a charcoal oven a year later.[3] He was also able to detect traces of chromium in precious gemstones, such as ruby or emerald.[2][4]

Molybdenite—the principal ore from which molybdenum is now extracted—was previously known as molybdena, which was confused with and often implemented as though it were graphite. Like graphite, molybdenite can be used to blacken a surface or as a solid lubricant.[5] Even when molybdena was distinguishable from graphite, it was still confused with a galena (a common lead ore), which took its name from Ancient Greek Μόλυβδος molybdos, meaning lead.[6] It was not until 1778 that Swedish chemist Carl Wilhelm Scheele realized that molybdena was neither graphite nor lead.[7][8] He and other chemists then correctly assumed that it was the ore of a distinct new element, named molybdenum for the mineral in which it was discovered. Peter Jacob Hjelm successfully isolated molybdenum by using carbon and linseed oil in 1781.[6][9]

In 1781, Carl Wilhelm Scheele discovered that a new acid, tungstic acid, could be made from scheelite (at the time named tungsten). Scheele and Torbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid.[10] In 1783, José and Fausto Elhuyar found an acid made from wolframite that was identical to tungstic acid. Later that year, in Spain, the brothers succeeded in isolating tungsten by reduction of this acid with charcoal, and they are credited with the discovery of the element.[11][12]

Historical development and uses

During the 1800s, chromium was primarily used as a component of paints and in tanning salts. At first, crocoite from Russia was the main source, but in 1827, a larger chromite deposit was discovered near Baltimore, United States. This made the United states the largest producer of chromium products until 1848 when large deposits of chromite where found near Bursa, Turkey.[13] Chromium was used for electroplating as early as 1848, but this use only became widespread with the development of an improved process in 1924.[14]

For about a century after its isolation, molybdenum had no industrial use, owing to its relative scarcity, difficulty extracting the pure metal, and the immaturity of the metallurgical subfield.[15][16][17] Early molybdenum steel alloys showed great promise in their increased hardness, but efforts were hampered by inconsistent results and a tendency toward brittleness and recrystallization. In 1906, William D. Coolidge filed a patent for rendering molybdenum ductile, leading to its use as a heating element for high-temperature furnaces and as a support for tungsten-filament light bulbs; oxide formation and degradation require that moly be physically sealed or held in an inert gas. In 1913, Frank E. Elmore developed a flotation process to recover molybdenite from ores; flotation remains the primary isolation process. During the first World War, demand for molybdenum spiked; it was used both in armor plating and as a substitute for tungsten in high speed steels. Some British tanks were protected by 75 mm (3 in) manganese steel plating, but this proved to be ineffective. The manganese steel plates were replaced with 25 mm (1 in) molybdenum-steel plating allowing for higher speed, greater maneuverability, and better protection.[6] After the war, demand plummeted until metallurgical advances allowed extensive development of peacetime applications. In World War II, molybdenum again saw strategic importance as a substitute for tungsten in steel alloys.[18]

In World War II, tungsten played a significant role in background political dealings. Portugal, as the main European source of the element, was put under pressure from both sides, because of its deposits of wolframite ore at Panasqueira. Tungsten's resistance to high temperatures and its strengthening of alloys made it an important raw material for the arms industry.[19]

Chemistry

H   He
Li Be   B C N O F Ne
Na Mg   Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba * Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra ** Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Uuq Uup Uuh Uus Uuo
 
  * La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
  ** Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
Group 6 element

Unlike other groups, the members of this family do not show patterns in its electron configuration, as two lighter members of the group are exceptions from the Aufbau principle:

Z Element Numerical Bohr model
24 chromium 2, 8, 13, 1
42 molybdenum 2, 8, 18, 13, 1
74 tungsten 2, 8, 18, 32, 12, 2
106 seaborgium 2, 8, 18, 32, 32, 12, 2

Most of the chemistry has been observed only for the first three members of the group, the chemistry of seaborgium is not very established and therefore the rest of the section deals only with its upper neighbors in the periodic table. The elements in the group, like those of groups 7—11, have high melting points, and form volatile compounds in higher oxidation states. All the elements of the group are relatively nonreactive metals with a high melting points (1907 °C, 2477 °C, 3422 °C); that of tungsten is the highest of all metals. The metals form compounds in different oxidation states: chromium forms compounds in all states from -2 to +6:[20] disodium pentacarbonylchromate, disodium decacarbonyldichromate, bis(benzene)chromium, tripotassium pentanitrocyanochromate, chromium(II) chloride, chromium(III) oxide, chromium(IV) chloride, potassium tetraperoxochromate(V), and chromium(VI) dichloride dioxide; the same is also true for molybdenum and tungsten, but the stability of the +6 state grows down the group.[20] Depending on oxidation states, the compounds are basic, amphoteric, or acidic; the acidity grows with the oxidation state of the metal.

Applications

  • Alloys[21]
  • Catalysts
  • Metallurgy, sometimes used in jet engines and gas turbines.[22]
  • Dyes and pigments
  • Tanning
  • hard materials

Biological occurrences

Group 6 is notable in that it contains some of the only elements in periods 5 and 6 with a known role in the biological chemistry of living organisms: molybdenum is common in enzymes of many organisms, and tungsten has been identified in an analogous role in enzymes from some archaea, such as Pyrococcus furiosus. In contrast, and unusually for a first-row d-block transition metal, chromium appears to have few biological roles, although it is thought to form part of the glucose metabolism enzyme in some mammals.

See also

Explanation of right side periodic table slice: Transition metals atomic number in black are solids solid borders are older than the Earth (Primordial elements) dotted borders are made artificially (Synthetic elements)

References

  1. ^ Cotterell, Maurice. (2004). The Terracotta Warriors: The Secret Codes of the Emperor's Army. Rochester: Bear and Company. ISBN 159143033X. Page 102.
  2. ^ a b c Guertin, Jacques; Jacobs, James Alan and Avakian, Cynthia P. (2005). Chromium (VI) Handbook. CRC Press. pp. 7–11. ISBN 9781566706087. 
  3. ^ Vauquelin, Louis Nicolas (1798). "Memoir on a New Metallic Acid which exists in the Red Lead of Sibiria". Journal of Natural Philosophy, Chemistry, and the Art 3: 146. http://books.google.com/?id=6dgPAAAAQAAJ. 
  4. ^ van der Krogt, Peter. "Chromium". http://elements.vanderkrogt.net/element.php?sym=Cr. Retrieved 2008-08-24. 
  5. ^ Lansdown, A.R. (1999). Molybdenum disulphide lubrication. 35. Elsevier. ISBN 9780444500328. 
  6. ^ a b c Emsley, John (2001). Nature's Building Blocks. Oxford: Oxford University Press. pp. 262–266. ISBN 0198503415. http://books.google.com/?id=j-Xu07p3cKwC&pg=PA265. 
  7. ^ Gagnon, Steve. "Molybdenum". Jefferson Science Associates, LLC. http://education.jlab.org/itselemental/ele042.html. Retrieved 2007-05-06. 
  8. ^ Scheele, C. W. K. (1779). "Versuche mit Wasserbley;Molybdaena". Svenska vetensk. Academ. Handlingar 40: 238. http://resolver.sub.uni-goettingen.de/purl?PPN324352840_0040. 
  9. ^ Hjelm, P. J. (1788). "Versuche mit Molybdäna, und Reduction der selben Erde". Svenska vetensk. Academ. Handlingar 49: 268. http://resolver.sub.uni-goettingen.de/purl?PPN324352840_0009_02_NS. 
  10. ^ Saunders, Nigel (February 2004). Tungsten and the Elements of Groups 3 to 7 (The Periodic Table). Chicago, Illinois: Heinemann Library. ISBN 1403435189. 
  11. ^ "ITIA Newsletter" (PDF). International Tungsten Industry Association. June 2005. http://www.itia.info/FileLib/Newsletter_2005_06.pdf. Retrieved 2008-06-18. 
  12. ^ "ITIA Newsletter" (PDF). International Tungsten Industry Association. December 2005. http://www.itia.info/FileLib/Newsletter_2005_12.pdf. Retrieved 2008-06-18. 
  13. ^ National Research Council (U.S.). Committee on Biologic Effects of Atmospheric Pollutants (1974). Chromium. National Academy of Sciences. pp. 155. ISBN 9780309022170. http://books.google.com/?id=ZZsrAAAAYAAJ. 
  14. ^ Dennis, J. K.; Such, T. E. (1993). "History of Chromium Plating". Nickel and Chromium Plating. Woodhead Publishing. pp. 9–12. ISBN 9781855730816. 
  15. ^ Hoyt, Samuel Leslie (1921). Metallography, Volume 2. McGraw-Hill. 
  16. ^ Krupp, Alfred; Wildberger, Andreas (1888). The metallic alloys: A practical guide for the manufacture of all kinds of alloys, amalgams, and solders, used by metal-workers ... with an appendix on the coloring of alloys. H.C. Baird & Co.. pp. 60. 
  17. ^ Gupta, C.K. (1992). Extractive Metallurgy of Molybdenum. CRC Press. ISBN 9780849347580. 
  18. ^ Millholland, Ray (1941-08). "Battle of the Billions: American industry mobilizes machines, materials, and men for a job as big as digging 40 Panama Canals in one year". Popular Science: pp. 61. 
  19. ^ Stevens, Donald G. (1999). "World War II Economic Warfare: The United States, Britain, and Portuguese Wolfram". The Historian (Questia). http://www.questia.com/googleScholar.qst;jsessionid=LY1PyzmCc1D256Gvh5wpbhxKyTyvcm2FHpMwpcs2wW2XyytCh4pW!956463030?docId=5001286099. 
  20. ^ a b Schmidt, Max (1968). "VI. Nebengruppe" (in German). Anorganische Chemie II.. Wissenschaftsverlag. pp. 119–127. 
  21. ^ "Molybdenum". AZoM.com Pty. Limited. 2007. http://www.azom.com/details.asp?ArticleID=616. Retrieved 2007-05-06. 
  22. ^ Bhadeshia, H. K. D. H.. "Nickel-Based Superalloys". University of Cambridge. http://www.msm.cam.ac.uk/phase-trans/2003/Superalloys/superalloys.html. Retrieved 2009-02-17. 

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Group 7 element — Group → 7 ↓ Period 4 25 Mn 5 …   Wikipedia

  • Group 11 element — Group → 11 ↓ Period 4 29 Cu 5 …   Wikipedia

  • Group 10 element — Group 10 redirects here. For the rugby league competition, see Group 10 Rugby League. Group → 4 ↓ Period 4 …   Wikipedia

  • Group 8 element — Group 8 redirects here. For the Swedish organization, see Group 8 (Sweden). A Group 8 element is one in the series of elements in group 8 (IUPAC style) in the periodic table, which consists of the transition metals iron (Fe), ruthenium (Ru),… …   Wikipedia

  • Group 12 element — A group 12 element is one in the series of elements in group 12 (IUPAC style) in the periodic table, consisting of transition metals which are zinc (Zn), cadmium (Cd), mercury (Hg), and ununbium (Uub). When compared with other groups of… …   Wikipedia

  • Group 5 element — A Group 5 element is one in the series of elements in group 5 (IUPAC style) in the periodic table, which consists of vanadium (V), niobium (Nb), tantalum (Ta), and dubnium (Db).All of these elements are classed in Group 5 because their valence… …   Wikipedia

  • Group 9 element — Group → 4 ↓ Period 4 27 Co 5 …   Wikipedia

  • Group 3 element — || Group 3/ungrouped | 7 || **ActinidesThe Group 3 elements are chemical elements comprising the third vertical column of the periodic table. IUPAC has not recommended a specific format for the periodic table, so different conventions are… …   Wikipedia

  • Group 4 element — In modern IUPAC nomenclature, Group 4 of the periodic table contains the following chemical elements: * titanium (Ti) * zirconium (Zr) * hafnium (Hf) * rutherfordium (Rf).This group lies in the d block of the periodic table. The group itself has… …   Wikipedia

  • Group 1 — * Group 1 element an element classification for Alkali metal * Group 1 (racing) a FIA classification for auto racing that preceded Group N * Group 1 thoroughbred horse races, are the leading events in the sport. * Group 1 Automotive a publicly… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.