This in an excerpt from this book
Modern Chemistry Lavoisier’s results and Atomic Theory provided chemists their first in depth understanding related to the nature of chemical reactions. Another cornerstone which dealt with the inherent property of all matter came a few years later in the form of atomic theory advanced in 1805 by an English schoolteacher, John Dalton. This theory puts forward the theory that matter constitutes of small particles which are named atoms and that chemical changes take place between atoms or groups of atoms. Finally, being equipped with in depth views about the nature of matter and of chemical reactions, chemistry began making rapid strides.

Very soon one after the other the gas laws of Joseph Louis Gay-Lussac and that of Joseph Louis Proust’s law of definite proportions came into being. In this period too came the hypothesis of Amedeo Avogadro, an Italian chemist, about the number of molecules in a volume of gas. To Dalton’s theory that the atoms of a single element have the same weight, Avogadro, in 1811, added the idea that one quart (or other volume) of a gas has the number of molecules which are exactly same as that of any other gas with an equal volume if both are allowed to rest at the same temperature and pressure.

His calculations also showed that if the gas is an element, such as hydrogen or oxygen, the atoms usually unite in pairs to form molecules (written H2, O2, and so on). The scientists knew, however, that equal volumes of different gases have unequal weights. Avogadro’s hypothesis implied that this showed relative weights of single atoms. This has been proved to be correct, and today Avogadro’s law may be stated thus: equal volumes of all gases under the same conditions of temperature and pressure contain the same number of molecules. Humphry Davy, about 1806, isolated a number of elements to add to the growing list.

Jons Jakob Berzelius, in 1826, analyzed hundred of compounds and published accurate tables of atomic weights. Friedrich Wohler’s synthesis of urea in 1828 proved that organic compounds could be made in the laboratory and opened a vast new field of chemistry. This began the development of the concept that organic compounds have geometric structure. Friedrich Kekule proposed cyclic (ring) structure of benzene about this time. Michael Faraday, formulated the laws of electrochemistry in 1834.

Mendeleev’s Basis for Modem Theory By the middle of the 19th century, about 60 elements were known John A.R. Newlands, Stanislao Cannizzaro, A.E.B. de Chancourtois and others had noticed that certain elements were much alike. The work of these men enabled Dmitri Mendeleev, in 1869, to publish the first periodic table. This table became the foundation of theoretical chemistry. To this period belongs Robert Bunsen, inventor of the Bunsen burner and of many instruments, including the spectroscope.

French chemist Louis Pasteur, one of the world’s great geniuses, shed new light on the relation between chemical composition and molecular structure by his discovery of the optical activity of some isomers. His work on antitoxins revolutionized biochemistry.


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