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Rhenium Compounds
Rhenium compounds are compounds formed by the transition metal rhenium (Re). Rhenium can form in many oxidation states, and compounds are known for every oxidation state from -3 to +7 except +2, although the oxidation states +7, +6, +4, and +2 are the most common. Rhenium is most available commercially as salts of perrhenate, including sodium and ammonium perrhenates. These are white, water-soluble compounds. Tetrathioperrhenate anion eS4sup>− is possible. Chalcogenides Oxides Rhenium(IV) oxide (or rhenium dioxide) is an oxide of rhenium, with the formula ReO2. This gray to black crystalline solid is a laboratory reagent that can be used as a catalyst. It adopts the rutile structure. It forms via comproportionation: :2 Re2O7 + 3 Re → 7 ReO2 Single crystals are obtained by chemical transport, using iodine as the transporting agent. At high temperatures it undergoes disproportionation. It forms perrhenates with alkaline hydrogen peroxide and oxidizing acids. In m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxidation State
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. Conceptually, the oxidation state may be positive, negative or zero. While fully ionic bonds are not found in nature, many bonds exhibit strong ionicity, making oxidation state a useful predictor of charge. The oxidation state of an atom does not represent the "real" formal charge on that atom, or any other actual atomic property. This is particularly true of high oxidation states, where the ionization energy required to produce a multiply positive ion is far greater than the energies available in chemical reactions. Additionally, the oxidation states of atoms in a given compound may vary depending on the choice of electronegativity scale used in their calculation. Thus, the oxidation state of an atom in a compound is purely a formalism. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxidizing Acid
An oxidizing acid is a Brønsted acid that is a strong oxidizing agent. Most Brønsted acids can act as oxidizing agents, because the acidic proton can be reduced to hydrogen gas. Some acids contain other structures that act as stronger oxidizing agents than hydrogen ions. Generally, they contain oxygen in their anionic structure. These include nitric acid, perchloric acid, chloric acid, chromic acid, and concentrated sulfuric acid, among others. General properties Oxidizing acids, being strong oxidizing agents, can often oxidize certain less reactive metals, in which the active oxidizing agent is not H+ ions. For example, copper is a rather unreactive metal, and has no reaction with concentrated hydrochloric acid. However, even dilute nitric acid can oxidize copper to Cu2+ ions, with the nitrate ions acting as the effective oxidant: : 3 Cu + 8 HNO3 → 3 Cu2+ + 2 NO + 4 H2O + 6 Sometimes the concentration of the acid is a factor for it to be strongly oxidizing. Again, copper ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Octahedral Molecular Geometry
In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The octahedron has eight faces, hence the prefix ''octa''. The octahedron is one of the Platonic solids, although octahedral molecules typically have an atom in their centre and no bonds between the ligand atoms. A perfect octahedron belongs to the point group Oh. Examples of octahedral compounds are sulfur hexafluoride SF6 and molybdenum hexacarbonyl Mo(CO)6. The term "octahedral" is used somewhat loosely by chemists, focusing on the geometry of the bonds to the central atom and not considering differences among the ligands themselves. For example, , which is not octahedral in the mathematical sense due to the orientation of the bonds, is referred to as octahedral. The concept of octahedral coordination geometry was developed by Alfred Wern ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perovskite (structure)
A perovskite is any material with a crystal structure following the formula ABX3, which was first discovered as the mineral called perovskite, which consists of calcium titanium oxide (CaTiO3). The mineral was first discovered in the Ural mountains of Russia by Gustav Rose in 1839 and named after Russian mineralogist L. A. Perovski (1792–1856). 'A' and 'B' are two positively charged ions (i.e. cations), often of very different sizes, and X is a negatively charged ion (an anion, frequently oxide) that bonds to both cations. The 'A' atoms are generally larger than the 'B' atoms. The ideal cubic structure has the B cation in 6-fold coordination, surrounded by an octahedron of anions, and the A cation in 12-fold cuboctahedral coordination. Additional perovskite forms may exist where either/both the A and B sites have a configuration of A1x-1A2x and/or B1y-1B2y and the X may deviate from the ideal coordination configuration as ions within the A and B sites undergo changes in thei ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Picometre
The picometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: pm) or picometer (American spelling) is a unit of length in the International System of Units (SI), equal to , or one trillionth of a metre, which is the SI base unit of length. The picometre is one thousand femtometres, one thousandth of a nanometre ( nm), one millionth of a micrometre (also known as a micron), one billionth of a millimetre, and one trillionth of a metre. The symbol μμ was once used for it. It is also one hundredth of an ångström, an internationally known (but non-SI) unit of length. Use The picometre's length is of an order so small that its application is almost entirely confined to particle physics, quantum physics, chemistry and acoustics. Atoms are between 62 and 520 pm in diameter, and the typical length of a carbon–carbon single bond is 154 pm. Smaller units still may be used to describe smaller particles (some of which are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ångström
The angstromEntry "angstrom" in the Oxford online dictionary. Retrieved on 2019-03-02 from https://en.oxforddictionaries.com/definition/angstrom.Entry "angstrom" in the Merriam-Webster online dictionary. Retrieved on 2019-03-02 from https://www.merriam-webster.com/dictionary/angstrom. (, ; , ) or ångström is a metric unit of length equal to m; that is, one ten-billionth ( US) of a metre, a hundred-millionth of a centimetre,Entry "angstrom" in the Oxford English Dictionary, 2nd edition (1986). Retrieved on 2021-11-22 from https://www.oed.com/oed2/00008552. 0.1 nanometre, or 100 picometres. Its symbol is Å, a letter of the Swedish alphabet. The unit is named after the Swedish physicist Anders Jonas Ångström (1814–1874). The angstrom is often used in the natural sciences and technology to express sizes of atoms, molecules, microscopic biological structures, and lengths of chemical bonds, arrangement of atoms in crystals,Arturas Vailionis (2015):Geometry of Crystals Lect ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crystal Structure
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystal, crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns that repeat along the principal directions of Three-dimensional space (mathematics), three-dimensional space in matter. The smallest group of particles in the material that constitutes this repeating pattern is the unit cell of the structure. The unit cell completely reflects the symmetry and structure of the entire crystal, which is built up by repetitive Translation (geometry), translation of the unit cell along its principal axes. The translation vectors define the nodes of the Bravais lattice. The lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, also called ''lattice parameters'' or ''cell parameters''. The symmetry properties of the crystal are described by the con ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cubic Crystal System
In crystallography, the cubic (or isometric) crystal system is a crystal system where the Crystal_structure#Unit_cell, unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals. There are three main varieties of these crystals: *Primitive cubic (abbreviated ''cP'' and alternatively called simple cubic) *Body-centered cubic (abbreviated ''cI'' or bcc) *Face-centered cubic (abbreviated ''cF'' or fcc, and alternatively called Close-packing_of_equal_spheres, ''cubic close-packed'' or ccp) Each is subdivided into other variants listed below. Although the ''unit cells'' in these crystals are conventionally taken to be cubes, the primitive_cell, primitive unit cells often are not. Bravais lattices The three Bravais lattices in the cubic crystal system are: The primitive cubic lattice (cP) consists of one Lattice_(group), lattice point on each corner of the cube; this means each simple cubic unit cell has in total one latt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Primitive Cell
In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessarily have unit size, or even a particular size at all. Rather, the primitive cell is the closest analogy to a unit vector, since it has a determined size for a given lattice and is the basic building block from which larger cells are constructed. The concept is used particularly in describing crystal structure in two and three dimensions, though it makes sense in all dimensions. A lattice can be characterized by the geometry of its unit cell, which is a section of the tiling (a parallelogram or parallelepiped) that generates the whole tiling using only translations. There are two special cases of the unit cell: the primitive cell and the conventional cell. The primitive cell is a unit cell corresponding to a single lattice point, it is the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dioxane
1,4-Dioxane () is a heterocyclic organic compound, classified as an ether. It is a colorless liquid with a faint sweet odor similar to that of diethyl ether. The compound is often called simply dioxane because the other dioxane isomers ( 1,2- and 1,3-) are rarely encountered. Dioxane is used as a solvent for a variety of practical applications as well as in the laboratory, and also as a stabilizer for the transport of chlorinated hydrocarbons in aluminum containers.Wisconsin Department of Health Services (20131,4-Dioxane Fact Sheet Publication 00514. Accessed 2016-11-12. Synthesis Dioxane is produced by the acid-catalysed dehydration of diethylene glycol, which in turn is obtained from the hydrolysis of ethylene oxide. In 1985, the global production capacity for dioxane was between 11,000 and 14,000 tons. In 1990, the total U.S. production volume of dioxane was between 5,250 and 9,150 tons. Structure The dioxane molecule is centrosymmetric, meaning that it adopts a chai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhenium
Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one of the rarest elements in the Earth's crust. Rhenium has the third-highest melting point and highest boiling point of any stable element at 5869 K. Rhenium resembles manganese and technetium chemically and is mainly obtained as a by-product of the extraction and refinement of molybdenum and copper ores. Rhenium shows in its compounds a wide variety of oxidation states ranging from −1 to +7. Discovered by Walter Noddack, Ida Tacke and Otto Berg in 1925, rhenium was the last stable element to be discovered. It was named after the river Rhine in Europe, from which the earliest samples had been obtained and worked commercially. Nickel-based superalloys of rhenium are used in combustion chambers, turbine blades, and exhaust nozzles ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon Monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simplest molecule of the oxocarbon family. In coordination complexes the carbon monoxide ligand is called carbonyl. It is a key ingredient in many processes in industrial chemistry. The most common source of carbon monoxide is the partial combustion of carbon-containing compounds, when insufficient oxygen or heat is present to produce carbon dioxide. There are also numerous environmental and biological sources that generate and emit a significant amount of carbon monoxide. It is important in the production of many compounds, including drugs, fragrances, and fuels. Upon emission into the atmosphere, carbon monoxide affects several processes that contribute to climate change. Carbon monoxide has important biological roles across phylogenetic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
