Groupe 6 du tableau périodique

Group 6, numbered by IUPAC style, is a group of elements in the periodic table. Its members are chromium (Cr), molybdenum (Mo), tungsten (W), and seaborgium (Sg). These are all transition metals and chromium, molybdenum and tungsten are refractory metals. The electron configuration of these elements do not follow a unified trend, though the outermost shells do correlate with trends in chemical behavior: "Group 6" is the new IUPAC name for this group; the old style name was "group VIB" in the old US system (CAS) or "group VIA" in the European system (old IUPAC). Group 6 must not be confused with the group with the old-style group crossed names of either VIA (US system, CAS) or VIB (European system, old IUPAC). That group is now called group 16. Chromium was first reported on 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. Though misidentified as a lead compound with selenium and iron components, the mineral was crocoite with a formula of PbCrO4. Studying the mineral in 1797, Louis Nicolas Vauquelin produced chromium trioxide by mixing crocoite with hydrochloric acid, and metallic chromium by heating the oxide in a charcoal oven a year later. He was also able to detect traces of chromium in precious gemstones, such as ruby or emerald. 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. 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. It was not until 1778 that Swedish chemist Carl Wilhelm Scheele realized that molybdena was neither graphite nor lead.