أكتوبر, 2018

 

Argon

Argon A chemical element, Ar, atomic number 18, and atomic weight 39.948. Argon is the third member of group 18 in the periodic table. The gaseous elements in this group are called the noble, inert, or rare gases, although argon is not actually rare. The Earth’s atmosphere is the only natural argon source; however, traces of this gas are found in minerals and meteorites. Argon constitutes 0.934% by…

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Ammine

Ammine One of a group of complex compounds formed by the coordination of ammonia molecules with metal ions and, in a few instances, such as calcium, strontium, and barium, with metal atoms. Although ammines are formally analogous to many salt hydrates, the general characteristics of the group of ammines differ considerably from those of the hydrates. For example, hydrated Co(III) salts are strong oxidizing agents whereas Co(II) ammines…

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Amino acids

Organic compounds possessing one or more basic amino groups and one or more acidic carboxyl groups. Of the more than 80 amino acids which have been found in living organisms, about 20 serve as the building blocks for the proteins. All the amino acids of proteins, and most of the others which occur naturally, are amino acids, meaning that an amino group (-NH2) and a carboxyl group (-COOH)…

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Ascorbic Acid

Ascorbic acid A white, crystalline compound, also known as vitamin C. It is highly soluble in water, which is a stronger reducing agent than the hexose sugars, which it resembles chemically. Vitamin C deficiency in humans has been known for centuries as scurvy.The compound has the structural formula shown below.

The stability of ascorbic acid decreases with increases in temperature…

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Amin

Amine A member of a group of organic compounds which can be considered as derived from ammonia by replacement of one or more hydrogens by organic radicals. Generally amines are bases of widely varying strengths, but a few which are actually acidic are known.

Amines constitute one of the most important classes of organic compounds. The lone pair of electrons on the amine nitrogen…

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Amid

Amide A derivative of a carboxylic acid with general formula RCONH2, where R is hydrogen or an alkyl or aryl radical. Amides are divided into subclasses, depending on the number of substituents on nitrogen. The simple, or primary, amides are considered to be derivatives formed by replacement of the carboxylic hydroxyl group by the amino group, NH2. They are named by dropping the “-ic acid” or “-oic acid”…

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Americium

A chemical element, symbol Am, atomic number 95. The isotope 241 Am is an alpha emitter with a half-life of 433 years. Other isotopes of americium range in mass from 232 to 247, but only the isotopes of mass 241 and 243 are important. The isotope 241Am is routinely separated from “old” plutonium and sold for a variety of industrial uses, such as 59-keV gamma sources and as…

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Aluminium – Aluminum

Aluminum A metallic chemical element, symbol Al, atomic number 13, atomic weight 26.98154, in group 13 of the periodic system. Pure aluminum is soft and lacks strength, but it can be alloyed with other elements to increase strength and impart a number of useful properties. Alloys of aluminum are light, strong, and readily formable by many metalworking processes; they can be easily joined, cast, or machined, and accept…

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Alum

A colorless to white crystalline substance which occurs naturally as the mineral kalunite and is a constituent of the mineral alunite. Alum is produced as aluminum sulfate by treating bauxite with sulfuric acid to yield alum cake or by treating the bauxite with caustic soda to yield papermaker salum. Other industrial alums are potash alum, ammonium alum, sodium alum, and chrome alum (potassium chromium sulfate). Major uses of…

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Alkyne

Alkyne One of a group of organic compounds containing a carbon-to-carbon triple-bond linkage (-C≡C-). They are termed acetylenes or alkynes. While exhibit­ing many of the characteristics of alkenes as regards unsaturation, the acetylenes have many unique properties. Since the bonding in alkyne molecules is linear. R-C≡C-R, cis-trans isomerism is not possible. In the simplest alkyne, acetylene (HC≡CH), or in monosubstituted acetylenes, the hydrogen attached to triply bonded carbon…

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