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Text 13 A

The History of Chemistry

 

Text 13 A The History of Chemistry - раздел Образование, Part One THE PREDICATE There Arc Five Periods In The History Of Chemistry. The Ancient Period Compri...

 
 

   

There arc five periods in the history of chemistry. The ancient period comprising the older civilizations of China, India, Greece, and their contemporaries to 350 A. D. developed practical arts as in Egypt, and a philosophical approach to the study of matter as in Greece, where a theory of numbers, an atomic theory, and a theory of five elements, earth, air, fire, water and die quintessence were proposed.

The alchemical period (350-1500), of which the principal goals were an elixir of life and the philosopher's stone by which base metals could be changed to gold, introduced pure substance and improved techniques.

Iatrochcmists (1500-1650) devoted their chemical pursuits to alleviation of disease. During the phlogiston period (1650-1774) men postulated a hypothetical matter whose presence was required for combustion and calcination. Gain in weight by calcination of metals led to a search for a very light material and subsequent discovery of gases, one of which was oxygen, and the answer to the problem. Ibis is the date when modern chemistry begins.

When qualitative and quantitative analysis had identified enough pure substances, inorganic chemistry grew in scope. Oiganic chemistry was little understood until 1828 when synthesis of urea by Fricdcrich Wohler (1800-1828), a German chemist, proved that the "vital force" which was considered imperative to produce compounds that occurrcd in living matter was not needed.

Meanwhile reliable physical and chemical measurement began with the laws of Boyle (1660), Charles (1785), Gay-Lussac (1808) and Dalton (1807). Dalton *s atomic theory (1807), postulated after the laws of the conservation of mass and definite proportions were tacitly assumed, stimulated the 19di-ccntury effort to determine accurate atomic weights, ideas for combination as expressed in valence[5], and the studies of molecular structure until the thrcc-dimcntional models appeared.

Gradual determination of physical properties of the elements indicated a periodicity of property expressed by the periodic law which has withstood the onslaught[6] of the discovery of the subatomic particles which make up the nucleus and outer electrons of the atom.


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