![]() an empirical formula) most often, in such materials, some small percentage of atoms are missing or too many atoms are packed into an otherwise perfect lattice work. Non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. ), in each case resulting in a material that is moved toward being measurably non-stoichiometric.Shown is a two-dimensional slice through a primitive cubic crystal system showing the regular square array of atoms on one face (open circles, o), and with these, places where atoms are missing from a regular site to create vacancies, displaced to an adjacent acceptable space to create a Frenkel pair, or substituted by a smaller or larger atom not usually seen (closed circles, Consequently, it is found with anionic oxygen carboxylate donors in methane monooxygenase, neutral and anionic nitrogen porphyrin donors in heme proteins, and sulfur cysteines and sulfides in ferridoxins and other iron-sulfur clusters.Chemical compounds that cannot be represented by an empirical formula Origin of title phenomenon in crystallographic defects. Many biological compounds contain iron(II), which is able to bind well to both hard and soft ligands. Iron is one of the most abundant elements on earth, and many iron compounds play important roles in biology. Many biologically important metal ions fall under the "borderline" category between hard and soft. In poplar plastocyanin, which aids in transferring electrons during reactions in the plant cell, the copper ion is coordinated to two nitrogen-donating histidines and two sulfur donors, a cysteine and a methionine. On the other hand, copper(I) is a soft acid. Calmodulin, which aids in calcium uptake, uses hard oxygen donors in aspartate and glutamate to bind to the Ca 2+. Relatively hard potassium ions bind to oxygen atoms in DNA to help stabilize the helix structure. In biology, metals display aspects of hard & soft acid & base chemistry. Propose a formula for a plausible mineral containing each of the following ions. Molybdenum(VI) can be found as powellite (calcium molybdenum oxide, CaMoO 4), but the most commonly mined ore contains molybdenum(IV), found in molybdenite (MoS 2). For example, iron(III) is often found as hematite (iron oxide, Fe 2O 3), whereas iron(II) can also be found as pyrite (iron sulfide, FeS). Some metals can pair with either hard or soft bases, particularly those metals from the middle of the transition metal group. Sulfides are the most common soft bases in geology, although the larger halides, like bromide and iodide, are also soft. Some prevalent minerals of soft metals are galena (lead sulfide, PbS 2) and cinnabar (mercury sulfide, HgS). Fluoride, carbonates, oxides, phosphates and sulfates are examples of hard bases. Some common minerals of hard metals are rutile (titanium oxide, TiO 2), dolomite (magnesium and calcium carbonate CaMg(CO 3) 2) and chromite (iron chromium oxide, FeCrO 4). There are some obvious HSAB applications in metallurgy and geology. Answer c:Īzide, which has a more polarizable, delocalized pi bonding system. Iodide, which is larger and more polarizable than chloride. Me 3P, because phosphorus is larger and more polarizable than nitrogen. Suggest which of the following bases is softer.Ĭ) amide (NH 2 -) or azide (N 3 -) Answer a: Conversely, AuF has never been isolated but AuF 3 (hard-hard) is stable. In keeping with the "like binds like" principle, the compound AuI (soft-soft) is stable, but AuI 3 (hard-soft) is unknown. The Au 3+ ion, because of its higher positive charge, is a harder acid than Au + and can form complexes with harder bases such as H 2O and amines. Netted solution pond next to cyanide heap leaching of gold ore near Elko, Nevada (1992). On the laboratory scale, cyanide plating solutions are typically disposed of by using bleach to oxidize CN - to OCN -, and the metal is recovered as an insoluble chloride salt. Cyanide, which is highly toxic, is gradually oxidized by air to the less toxic cyanate (OCN -) ion. In 2000, a spill at Baia Mare, Romania resulted in the worst environmental disaster in Europe since Chernobyl. The use of cyanide ion on a large scale in mining, however, creates a potentially serious environmental hazard. The precious metals are then isolated from the solution using chemical reducing agents or by electroplating. Ag is similarly dissolved by air oxidation in cyanide solutions. This reaction is used in gold mining to separate small flakes of Au from large volumes of sand and other oxides.
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