History of Chemistry and the impact of the atomic theory
The first practical knowledge of chemistry deals with ceramics, and dyes, these crafts have been developed with considerable skill, but without an understanding of the principles involved, and in 3500 BC in Egypt and Mesopotamia. The basic ideas of the elements and compounds were first formulated by Greek philosophers during the period 500 to 300 BC C. Opinion varied, but generally believed that four elements (fire, air, water and earth) combined to form all things. Aristotle's definition of a simple body as "one in which other bodies can be decomposed and itself is not capable of being divided "is close to the modern definition of element.
About the beginning of the Christian era in Alexandria, the ancient art Egyptian and Greek philosophical speculations were fused industry in a new science. The beginnings of chemistry as it was known first, mix with the occult and magic. Interest of the period were the transmutation of metals into gold, imitation precious stones, and the search for the elixir of life, which is believed to grant immortality. Muslim conquests in the 7th century AD spread the remains of Hellenistic civilization in the Arab world. The first chemical treatises is well known in Europe were translations into Latin of Arabic works, made in Spain CAD 1100, so it is often erroneously supposed that chemistry originated among the Arabs. Alchemy widely developed during the Middle Ages, cultivated largely by itinerant scholars who wandered over Europe for clients.
In the hands of the "chemical Oxford "(Robert Boyle, Robert Hooke, and John Mayow) chemistry began to emerge in contrast to the pseudoscience of alchemy. Boyle (1627-91) is often called the founder of modern chemistry (sometimes also an honor given Antoine Lavoisier, 1743-94). Experiments were conducted at reduced pressure, using an air pump, and discovered the volume and pressure are inversely related in gases. Hooke gave the first rational explanation of the combustion, such as combination with air, while Mayow studied animal respiration. Although the English chemists were moving toward the theory proper combustion, two Germans, JJ Becher and GE Stahl, introduced the false phlogiston theory of combustion, which held that the substance phlogiston is contained in all combustible bodies and escapes when the body burns.
The discovery of several gases and the analysis of air as a mixture of gases occurred during phlogiston period. Carbon dioxide, first described by JB van Helmont and rediscovered by Joseph Black in 1754, was originally called fixed air. Hydrogen, discovered by Boyle and carefully studied by Henry Cavendish, was called inflammable air and sometimes identified with phlogiston itself. Cavendish also showed that explosion of hydrogen and oxygen produces water. CW Scheele found that air is composed of two fluids, only one of which supports combustion. He was the first to get pure oxygen (1771-73), although not recognized as an element. Joseph Priestley discovered oxygen independently by heating the oxide red mercury with a burning glass, was the last great defender of the phlogiston theory.
The work of Priestley, Black, and Cavendish was radically reinterpreted by Lavoisier, who did for chemistry what Newton had done for physics a century before. He made important new discoveries of their own, but was a theorist. He recognized the true nature of combustion, introduced a new chemical nomenclature, and wrote the first textbook of modern chemistry. It is erroneously that all acids contain oxygen.
The assumption that compounds were of definite composition was implicit in the chemistry of the 18th century. JL Proust formally stated the law of constant proportions in 1797. CL Berthollet opposed this law, considering that the composition depends on the method of preparation. The matter was resolved in favor of Proust by John Dalton's atomic theory (1808). The atomic theory goes back to the Greeks, but was not successful Dalton's chemistry to the relative weight assigned to the atoms of the substance elements. Electrochemical theories of chemical combinations were developed by Humphry Davy and JJ Berzelius. Davy discovered the alkali metals by passing an electric current through their molten oxides. Michael Faraday discovered that a certain amount charge must flow to deposit a given weight of material in solution. Amedeo Avogadro introduced the hypothesis that equal volumes of gases at the same pressure and temperature contain the same number of molecules.
William Prout suggested that all the elements seemed to have atomic weights that were multiples of the weight atomic hydrogen, they could all be somewhat different combinations of hydrogen atoms. This contributed to the concept of periodic table of elements, the culmination of a long and systematic effort to find the periodic properties of the elements. laws and standards were presented almost simultaneously and independently by JL Meyer in Germany and DI Mendeleev in Russia (1869). A win at the beginning of the new theory was the discovery of new elements that fit spaces gaps in the table. William Ramsay's discovery, in collaboration with Lord Rayleigh, argon and other inert gases in the atmosphere extended the periodic table
About the Author
Dr. Badruddin Khan teaches Chemistry in the University of Kashmir, Srinagar, India.
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