Dictionary, Defintion, Meaning, What is Corundum, Covalent Radius, Copper Sulphides, Cordite, Corrosion, Cortisone

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Home >> Chemistry Dictionary >> Corundum Covalent Radius

Your Ad Here	Copper sulphides. Copper(II) sulphide, CuS. Black solid, Cu plus excess S or copper(II) salt plus H₂S. Decomposes to copper(I) sulphide, Cu₂S, on heating. Cordite. An explosive mixture of cellulose nitrate and nitroglycerin, with added plasticizers and stabilizers, used as a propellant for guns. Corrosion. Chemical of electrochemical attack on the surface of a metal by which some substance in its environment and converted into unwanted compound, e.g. rusting of iron. Cortisone. C₂₁H₂₈O₅. m.p.215ºC. A steroid.
Cortisone is a harmone produced by the cortex of the adrenal glands. As with other adrenal corticoid steroids, administration of cortisone leads to an increased deposition of liver glycogen. It can remove features of rheumatoid arthritis, but check the underlying disease: it is used various diseases of the eye, and is an antiallergic and antifibroplastic agent. Corundum. A mineral form of aluminium oxide, Al₂O₃. It crystallizes in the trigonal system and occurs as well-developed hexagonal crystals.
It is colourless and transparent when pure but the presence of other elements gives rise to a variety of colours. Ruby is a red variety containing chromium; sapphire is a blue variety containing iron and titanium. Corundum occurs as a rock-forming mineral in both metamorphic and igneous rocks. It is chemically resistant to weathering processes and so also occurs in alluvial (placer) deposits. The second hardest mineral after diamond (it has a hardness of 9 on the Mohs’ scale), it is used as an abrasive. Critical temperature. The maximum temperature at which a gas can be liquefied. Above this temperature, a liquid state of a substance cannot exist. Symbol T.	Your Ad Here
Coulomb. Symbol C. The SI unit of electric charge. It is equal to the charge transferred by a one ampere in one second. The unit is named after Charles de Coulomb (1736-1806), a French physicist. Coulometer. A instrument or device for measuring the amount of charge (number of coulombs) passing in an electrical circuit. Covalent atomic solids. A crystal solid in which the points of crystal lattice are occupied by atoms which share electrons with their neighbours.
Your Ad Here	The covalent bonds are quite strong as a result the solids are quite hard, having a high melting point, and are poor conductor of electricity, e.g., diamond. Covalent bond. A bond formed when a pair of electrons is being shared by atoms, e.g., the bond formed by two hydrogen atoms. Covalent radius. An effective radius assigned to an atom in a covalent compound. In the case of a simple diatomic molecule, the covalent is half the distance between the nuclei. Thus, in Cl₂ the internuclear distance is. 198 nm so the covalent radius is taken to be 0.099 nm.

Covalent radii can also be calculated for multiple bonds; for instance, in the case of carbon the values are 0.077 nm for single bonds, 0.0665 nm for double bonds, and 0.0605 nm for triple bonds. The values of different covalent radii can sometimes by added to give internuclear distance. For example, the length of the bond in interhalogens (e.g. ClBr) is nearly to the sum of the covalent radii of the halogens involved. However, this is not always true because of other effects (e.g. ionic contributions to the bonding).
Cracking. The process of breaking down chemical compounds by heat. The term is applied particularly to the cracking of hydrocarbonds in the kerosine fraction obtained form petroleum refining to gives smaller hydrocarbons and alkenes. It is an important process, both as motor fuel) and as a source of branched-chain hydrocarbons suitable for gasoline (for motor fuel) and as a source of ethane and other alkenes. Catalytic cracking is a similar process in which a catalyst is used to lower the temperature required and to modify the products obtained.

Creep. The slow yielding of alloys and metals under a load which does not cause fracture. The process is diffusion controlled.

Cross linkage. Refers to a short side chain of atoms which is linking two linger chains in a polymeric material.

Cross section. A number denoting the effective area of a nucleus for a scattering or asbroption process.

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