أكتوبر 15th, 2018

 

Alkaline-earth metals

Usually calcium, strontium, and barium, the heav­iest members of group 2 of the periodic table (excepting radium). Other members of the group are beryllium, magnesium, and radium, sometimes included among the alkaline-earth metals. Beryllium resembles aluminum more than any other element, and magnesium behaves more like zinc and cadmium. The gap between beryllium and magnesium and the remainder of the elements of group 2 makes it desirable to…

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Alkali

Any compound having highly basic properties, strong acrid taste, and ability to neutralize acids. Aqueous solutions of alkalies are high in hydroxyl ions, have a pH above 7, and turn litmus paper from red to blue. Caustic alkalies include sodium hydroxide (caustic soda), the sixth-largest-volume chemical produced in the United States, and potassium hydroxide. They are extremely destructive to human tissue; external burns should be washed with large amounts…

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Alicyclic hydrocarbon

An organic compound that contains one or more closed rings of carbon atoms. The term alicyclic specifically excludes carbocyclic com­pounds with an array of n-electrons characteristic of aromatic rings. Compounds with one to five alicyclic rings of great variety and complexity are found in many natural products such as steroids.and terpenes. By far the majority of these have six-membered rings.

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aldehydes

One of a class of organic chemical compounds represented by the general formula RCHO. Formaldehyde, the simplest aldehyde, has the formula HCHO, where R is hydrogen. For all other aldehydes, R is a hydrocarbon radical which may be substituted with other groups such as halogen or hydroxyl (see table). Because of their high chemical reactivity, aldehydes are important intermediates for the manufacture of resins, plasticizers, solvents, dyes, and…

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Alcohol

A member of a class of organic compounds composed of carbon, hydro­gen, and oxygen. They can be considered as hydroxyl derivatives of hydrocarbons produced by the replacement of one or more hydrogens by one or more hydroxyl (R-OH) groups.

Classification. Alcohols may be mono-, di-, tri-, or polyhydric, depending upon the number of hydroxyl groups they possess. They are classified as primary (RCH2OH), secondary (R2CHOH), or tertiary (R3COH),…

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