3 Part One. The Predicate

The Study of the Structure of Molecules
The study o f the structure o f molecules was originally carried on by chemists using methods of investigation that were essentially chemical in nature, relating to the chemical composition of a substance, the existence o f isomers, the nature of the chemical reactions in which a substance takes part and so on. From the consideration of facts o f this kind Frankland, Kckulc, Coupcr and Butlerov were led a century ago to formulate the theory of valence and to write the first structural formulas for molecules, van’t Hoff and le Bel were led to bring classical organic stereochemistry into its final form by their brilliant postulate of the tetrahedral orientation of the four-valence bonds of the carbon atom, and Werner was led to his development of the theory of the stereo­chemistry of complex inorganic substances.

In the nineteenth century the valence bond was represented by a line drawn between the symbols of two chemical elements, which expressed in a concisc way many chemical facts, but which had only qualitative significance with regard to molecular structure. The nature of the bond was completely unknown. After the discovery of the electron, numerous attempts were made to develop an electronic theory of the chemical bond. These culminated in the work of Lewis, who in his 1916 paper, which forms the basis of the modem electronic theory of valence, discussed not only the formation of ions by the completion of stable shells of electrons but also the formation of a chemical bond, now called the covalcnt bond, by the sharing of the two electrons between two atoms. Lewis further emphasized the importance of the phenomena of the pairing of unshared as well as of shared electrons and of the stability of the group of eight electrons (shared or unshared) about the lighter atoms. These ideas were then further developed by many investigators; the work of Langmuir was especially valuable in showing the great extent to which the facts of chemistry could be coordinated and clarified by the application of the new ideas. Many of the features of the detailed theory that is discusscd were suggested in the papers of Langmuir and others written in the decadefollowing 1916, or in (he book Valence and Structure of Atoms and Moleculeswritten by Lewis in 1923.

All of these early studies, however, contained, in addition to suggestion that have since been incorporated into the present theory, many others that have been discarded.
Words and Word-Combinations to Be Memorized

complex, consideration, coordinate, decade, discard, discuss, draw, especially, essentially, formation, incorporate, lead to, line, numerous, originally, paper, phenomenon, with regard to, relate, and so on, stability, stable, structural, take part, valence, valuable

Ex. 5. Give the Uzbek equivalents fo r th e following:

cany on the study, essentially chemical in nature, take part in a reaction, from the consideration of facts, formulate the theory of valence, structural formulas for molecules, final form, tetrahedral orientation of the bonds, represent the bond by a line, draw a line between, have qualitative significance, with regard to molecular structure, form the basis of a theory, share the electrons between the atoms, the features of the detailed theory, be incorporated into

Ex. 6. Give the English equivalents for the following:

molekulalarning tuzilishini o'rganish, tadqiqot usullari, dastlab kimyoviy tarkibi, izomerlarning mavjudligi, kimyoviy reaktsiyaning tabiati va boshqalar, reaktsiyada ishtirok eting, bunday dalillar, bir asr oldin, tarkibiy formulani, uglerod atomining to'rt valentli bog'lanishini, stereoximiya nazariyasini yozing. chiziq, ko'p sonli urinishlar, urinishlar qilish, nazariya, elektron valentlik nazariyasini ishlab chiqish, kimyoviy bog'lanishni shakllantirish, kovalent aloqa, elektronlarni smth o'rtasida ajratish, smning ahamiyatini ta'kidlash, yangi foydalanish. dei, birinchi tadqiqotlar tashqari

Ex. 7. Fill in th e b lan k s w ith prepositions where necessary.

1. Early chemists carried ... the study ... the structure ... molecules ... the methods that were essentially chemical ... nature. 2. The first structural formulas ... molecules were written ... more than a century ago. 3 .... the 19th century the valence bond was represented ... a line ... the symbols ... two chemical elements. 4. The nature ... the bond was completely unknown. 5. ... the discovery ... the electron attempts were made to develop an electronic theory ... the chemical bond. 6 .... 1916 Lewis formed ... the basis ... the modem electronic theory ... valence. 7. Early studies contained ... some suggestions that were discarded later.

Ex. 8. Translate the sentences into Uzbek, paying attention to different functions of the word regard.

1. At the beginning of the 19th century, atoms were regardedas the smallest constituent particles of matter. 2. Equal volumes of gases are stated to contain the same number of molecules at the same temperature and pressure, regardlessof composition. 3. Unfortunately, it’s not always that the young have great regardto their parents. 4. Particular attention must be paid to the chaptcr regardingthe conditions of synthesis. 5. Many chemical facts were described which had only qualitative significance with regardto molecular structure. 6. The work of Lewis was most important as regardsthe development of the electronic theory of valence.

Ex. 9. Translate the sentences into Uzbek.

a) 1. These results are not in agreement with the theory. 2. They did their work in time. 3. Register the readings and then begin the calculations.4. Put the burner on the table. 5. The discovery of the electron stimulated the development of an electronic theory. 6. The information was given to a numerous audicncc. 7. The rate of the reaction often depends on the temperature. 8. The heating resulted in the explosion. 9. Give this instruction to the students. 10. Give the students this instruction.11. Lowering the temperature of a liquid lessens the kinetic energy.12. Hydrogen-has 3 isotopes. 13. The study of the structure of molecules has been carried on by scientists since early times..

b) 1. Have you seen him? 2. Did you speak to her yesterday? 3 .1 don’t know anything about the author of this monograph. Do you know anything about him? 4. It is a very good apparatus, everybody likes to work with it.5. The bottle with H₂SO₄ is on that shelf, bring it, please. 6. The temperature must be 25°C, don’t forget it. 7. They think it necessary to attend all the seminars. 8. The teacher made it dear that the examination will be difficult to pass. 9. Avogadro’s principle let one calculate the number of molecules per gram mole of a gas. 10. Chemistry helps one to understand other fields of science better. 11. The properties of HCl make it a useful laboratory reagent. 12. Consideration of all the facts enabled us to draw a very important conclusion. 13. They don’t think it possible to work with this substance, it is not pure enough.
Ex. 10. Translate the sentences into English.

1. Molekula tuzilishi muammosi har doim kimyogarlarni qiziqtirib kelgan.

2. Strukturaviy formula bu elementlarning qanday guruhlanganligini va bog'lanishlarning molekulada qanday taqsimlanishini ko'rsatadigan formula. Butlerov tarkibiy formulani yozgan birinchi rus olimi edi. 4. 19-asrda valentlik aloqasi ikkita kimyoviy elementning belgilari orasidagi chiziq bilan ifodalangan. 5. Keyin ulanishlarning tabiati to'liq noma'lum edi, 6. Molekulalar tuzilishini o'rganishda izomerizm mavjudligi aniqlandi. Izomerlar bir xil molekulyar formulaga ega bo'lgan, ammo turli xil tuzilmalardir.
Ex. 11. Answer (he following questions:

1. Whal methods were used in the first investigations of the structure of molecules? 2. What do you know about isomers? 3. Who formulated the theory of valence? 4. What is particularly interesting as regards the valence bonds of the carbon atom? 5. In what way was the valence bond represented?6. How did the discovery of the electron affect the development of an electronic theory? 7. What do you know about the work of Lewis?