مصادر الكيمياء موقع لتعليم الكيمياء بصورة مبسطة

Atomic mass : The mass of an atom or molecule on a scale where the mass of a carbon-12 (12C) atom is exactly 12.0. The mass of any atom is approximately equal to the total number of its protons and neutrons multiplied by the atomic mass unit, u = 1.6605397 x 10-24 gram. (Electrons are much lighter, about 0.0005486 u.) …

Atom A constituent of matter consisting of z negatively charged electrons bound predominantly by the Coulomb force to a tiny, positively charged nucleus consisting of Z protons and (A – Z) neutrons. Z is the atomic number, and A is the mass or nucleon number. The atomic mass unit is u = 1.6605397 x 10-24 g. Electrically neutral atoms (z …

Art conservation chemistry The application of chemistry to the technical examination, authentication, and preservation of cultural property. Chemists working in museums engage in a broad range of investigations, most frequently studying the chemical composition and structure of artifacts, their corrosion products, and the ma­terials used in their repair, restoration, and conservation. The effects of the museum environment, including air pollutants, …

Aromatic hydrocarbon A hydrocarbon with  a chemistry similar to that of benzene. Aromatic hydrocarbons are either benzenoid or nonbenzenoid. Benzenoid aromatic hydrocarbons contain one or more benzene rings and are by far the more common and the more important commercially. Nonbenzenoid aromatic hydrocarbons have carbon rings that are either smaller or larger than the six-membered benzene ring. Their importance arises …

Aqua regia A mixture of one part by volume of concentrated nitric acid and three parts of concentrated hydrochloric acid. Aqua regia was so named by the alchemists because of its ability to dissolve platinum and gold. Either acid alone will not dissolve these noble metals.

Antimony A chemical element, symbol Sb, atomic number 51. Antimony is not a naturally abundant element; it is occasionally found native, often in isomorphous mixture with arsenic, as allemonite. The symbol Sb is derived from the Latin name stibium. The element is dimorphic, existing as a yellow, metastable form composed of Sb4 molecules, as in antimony vapor and the structural …

Ammonium salt A product of a reaction between ammonia, NH3, and various acids. The general reaction for formation is NH3 + HX –+ NH2X. Examples of ammo­nium salts are ammonium chloride, NH4Cl, ammonium nitrate, NH4NO3,  These compounds are ad­dition products of ammonia and the acid. For this reason, their formulas are sometimes written as [H(NH3)]X. All ammonium salts decompose into …

Ammonia The most familiar compound composed ‘of the elements nitrogen and hydrogen, NH3. It is formed as a result of the decomposition of most nitrogenous organic material, and its presence is indicated by its pungent and irritating odor. Ammonia has a wide range of industrial and agricultural applications. Examples of its use are the production of nitric acid and ammonium …

Aspirin The acetyl ester of salicylic acid, also known as 2-(acetyloxy)-benzoic acid and acetylsalicylic acid (see structure below). Aspirin is prepared by the acetylation of salicylic acid with acetic anhydride. Aspirin is effective as an analgesic, antipyretic, and anti-inflammatory drug. It pre­vents the aggregation of platelets, and there is some evidence that it can prevent stroke. Aspirin, if tolerated, is …

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 …