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Vanadium and Chromium Groups
Published in Brian D. Fath, Sven E. Jørgensen, Megan Cole, Managing Global Resources and Universal Processes, 2020
The vanadium group of elements consists of vanadium (V), niobium (Nb, previously called columbium), tantalum (Ta), and dubnium (Db). The vanadium metals lie in the d-block of the periodic table and are found in Group 5. The chromium group consists of chromium (Cr), molybdenum (Mo), tungsten (W), and seaborgium (Sg). Dubnium and seaborgium are synthetic elements whose most stable isotopes are 108268Db(t1/2=28hr) and 106271Sg(t1/2=1.9min);[1] thus, these two elements are not discussed here. Chromium and tungsten are probably the most familiar metals of the two groups of elements. This is because of chromium’s role in the manufacture of stainless steel and the famous use of tungsten as a filament in lightbulbs. This entry summarizes the impact of V, Nb, Ta, Cr, Mo, and W contaminations on the environment and human, animal, and plant health. The geochemical occurrences of these elements are first discussed to establish an understanding of their natural distribution in the environment. These elements are widely used in various industrial applications, especially in metal industries; their applications and levels in the environment are discussed next. Potential sources of these elements, which humans and the environment can be exposed to, are described in some details. Finally, the metabolism, health effects, and regulatory measures taken to reduce or prevent the release of such trace metals to the environment are also discussed.
Properties of the Elements and Inorganic Compounds
Published in W. M. Haynes, David R. Lide, Thomas J. Bruno, CRC Handbook of Chemistry and Physics, 2016
W. M. Haynes, David R. Lide, Thomas J. Bruno
The Dubna Team, directed by Flerov and Organessian, produced heavy ions of 54Cr with their 310-cm heavy-ion cyclotron to bombard 207Pb and 208Pb and found a product that decayed with a half-life of 7 ms. They assigned 259106 to this isotope. It is now thought seven isotopes of Seaborgium have been identified. Two of the isotopes are believed to have halflives of about 30 s. Seaborgium most likely would have properties resembling tungsten. The IUPAC adopted the name Seaborgium in August 1997. Normally the naming of an element is not given until after the death of the person for which the element is named; however, in this case, it was named while Dr. Seaborg was still alive. Selenium -- (Gr. Selene, moon), Se; at. wt. 78.96(3); at. no. 34; m.p. (gray) 221 °C; b.p. (gray) 685 °C; sp. gr. (gray) 4.79, (vitreous) 4.28; valence -2, +4, or +6. Discovered by Berzelius in 1817, who found it associated with tellurium, named for the Earth. Selenium is found in a few rare minerals, such as crooksite and clausthalite. In years past it has been obtained from flue dusts remaining from processing copper sulfide ores, but the anode muds from electrolytic copper refineries now provide the source of most of the world's selenium. Selenium is recovered by roasting the muds with soda or sulfuric acid, or by smelting them with soda and niter. Selenium exists in several allotropic forms. Three are generally recognized, but as many as six have been claimed. Selenium can be prepared with either an amorphous or crystalline structure. The color of amorphous selenium is either red, in powder form, or black, in vitreous form. Crystalline monoclinic selenium is a deep red; crystalline hexagonal selenium, the most stable variety, is a metallic gray. Natural selenium contains six stable isotopes. Twentynine other isotopes and isomers have been characterized. The element is a member of the sulfur family and resembles sulfur both in its various forms and in its compounds. Selenium exhibits both photovoltaic action, where light is converted directly into electricity, and photoconductive action, where the electrical resistance decreases with increased illumination. These properties make selenium useful in the production of photocells and exposure meters for photographic use, as well as solar cells. Selenium is also able to convert a.c. electricity to d.c., and is extensively used in rectifiers. Below its melting point, selenium is a p-type semiconductor and is finding many uses in electronic and solid-state applications. It is used in xerography for reproducing and copying documents, letters, etc., but recently its use in this application has been decreasing in favor of certain organic compounds. It is used by the glass industry to decolorize glass and to make ruby-colored glasses and enamels. It is also used as a photographic toner, and as an additive to stainless steel. Elemental selenium has been said to be practically nontoxic and is considered to be an essential trace element; however, hydrogen selenide and other selenium compounds are extremely toxic, and resemble arsenic in their physiological reactions. Hydrogen selenide in a concentration
Chemistry of superheavy transition metals
Published in Journal of Coordination Chemistry, 2022
As is well known, most of it is gas-phase chemistry [49] in the form of atom-by-atom experiments due to the aforementioned limited availability of produced isotopes. While fast gas-phase experiments were carried out for longer-living elements of groups 4–8 (Rf through Hs) and 12 (Cn), for solution chemistry to be explored lifetimes higher than a few seconds are required (in addition to measurable quantities). In this light, seaborgium (270±1Sg isotopes have lifetimes of ∼2 min) is currently the heaviest 6d element for which simple chemistry experiments may be conceived and possibly realized. No volatile compounds are known yet for Mt, Ds, and Rg due to an unfavorable combination of their production rate and half-life.