3 Part One. The Predicate

The Development of the Theory of Valence
Modem structural chemistry differs from classical structural chemistry with respect to the detailed picture of molecules and crystals that it presents. By various physical methods, including the study of the structure of crystals by the diffraction of X-rays and o f gas molecules by the diffraction of electron waves, the measurement of electric and magnetic dipole 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 o f molecules and crystals and even their electronic structures; a discussion of valence and the chemical bond now must take into account this information as well as the facts of chemistry.

The rcfinmcnt of the electronic theory of valence into its present form has been ducf 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 molecules, leading to the complete elucidation of the phenomena involved in the formulation of a covalcnt 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 chemical theory a new concept, that of resonance, which, if not entirely unanticipated in its applications to chemistry, nevertheless, has not before been clcarly rccognizcd and understood.

Mashq 3. Matnning asosiy tarkibini bir nechta jumlalarga quying.

Mashq 4. Matnning rejasini tuzing.

Mashq 5. Jumlalarni o'qing va matn tarkibiga mos kelishini ayting. Agar yo'q bo'lsa, ularni tuzating.

1. Structural chemistry hasn’t changed since the 19th century. 2. The pictures of molecules presented by modem chemistry and classical structural chemistry are not the same. 3. Electronic structures are investigated only by chemical methods. 4. The development of the theory of quantum mechanics affeetcd the refinement of the electronic theory.5. A concept of rcsonancc was introduced in terms o f the theory of quantum mechanics. 6. Application of quantum mechanics enabled scientists to develop a method for the calculation of the properties of simple molecules.