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РЕГИСТРАЦИЯ ЭКСКУРСИЯ

Text 19 В

Прочтите текст про себя (контрольное время чтения — 3 минуты). The Development of the Theory of Valence

Modern structural chemistry differs from classical structural chemistry with respect to the detailed picture of molecules and ciystals that it presents. By various physical methods, including the study of the structure of crystals by the diffraction of X-rays and of gas molcculcs by the diffraction of electron waves, the measurement of electric and magnetic dipolc moments, the interpretation of band spectra, line spectra, microwave spectra, and nuclear magnetic resonance spectra, and the determination of entropy values, a great amount of information has been obtained about the atomic configurations of molcculcs and crystals and even their electronic

structures; a discussion of valcncc and the chcmical bond now must take into account this information as well as the facts of chemistry.

The rcfinmcnt of the clcctronic theory of valcncc into its present form has been due" almost entirely to the development of the theory of quantum mechanics, which has not only provided a method for the calculation of the properties of simple molccules, leading to the complete elucidation of the phenomena involved in the formulation of a covalent bond between two atoms and dispersing the veil of mystery that has shrouded the bond during the decades since its existence was first assumed, but has also introduced into chcmical theory a new concept, that of resonance, which, if not entirely unanticipated in its applications to chemistry, nevertheless, has not before been clearly recognized and understood.


19.01.2015; 01:15
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