The study of the structure of molcculcs was originally earned on by chemists using methods of investigation that were essentially chcmical in nature, relating to the chemical composition of a substancc, the existence of isomers, the nature of the chemical reactions in which a substance takes part and so on. From the consideration of facts of this kind Frankland, Kekulc, Couper and Butlcrov were led a century ago to formulate the theory of valcncc and to write the first structural formulas for molcculcs, van't Hoff and lc Bel were led to bring classical organic stereochemistry into its final form by their brilliant postulate of the tctrahcdral 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 substanccs.
In the nineteenth century the valcncc bond was represented by a line drawn between the symbols of two chcmical 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 chcmical bond. These culminated in the work of Lewis, who in his 1916 paper, which forms the basis of the modern clcctronic theory of valcncc, discussed not only the formation of ions by the completion of stable shells of electrons but also the formation of a chcmical bond, now called the covalent 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 decade
following 1916 or in the book Valence and Structure of Atoms and Molecules written 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
Complcx, consideration, coordinate, dccadc, 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, valcnce, valuable
Ex. 5. Give the Russian equivalents for the following:
carry on the study, essentially chcmical in nature, take part in a reaction, from the consideration of facts, formulate the theory of valence, structural formulas for molcculcs, final form, tctrahcdral 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:
вивчення структури молекул, методи дослідження, спочатку, хімічний склад, існування ізомерів, природа хімічної реакції, і так далі, взяти участь в реакції, такого роду факти, століття тому, написати структурну формулу, чотири валентні зв'язки атома вуглецю, теорія стереохимии, провести лінію, численні спроби, зробити спробу, розвинути теорію, електронна теорія валентності, утворення хімічного зв'язку, ко валентний зв'язок, поділити електрони між чомусь л., підкреслити значення чого-л., застосування нових ідей, запропонувати теорію, крім, перші дослідження
Ex. 7. Fill in the blanks with prepositions where necessary.
1. Early chemists carried ... the study ... the structure ... molcculcs ... the methods that were essentially chcmical ... nature. 2. The first structural formulas ... molecules were written ... more than a ccntury ago. 3. ... the 19th ccntuiy the valcnce bond was represented ... a line ... the symbols ... two chcmical elements. 4. The nature ... the bond was completely unknown. 5. ... the discovery ... the electron attempts were made to develop an electronic theory ... the chcmical bond. 6. ... 1916 Lewis formed ... the basis ... the modern electronic theory ... valence. 7. Early studies contained ... some suggestions that were discarded later.
Ex. 8. Translate the scntcnccs into Russian, paying attention to different functions of the word regard.
I. At the beginning of the 19th ccntuiy, atoms were regarded as the smallest constituent particles of matter. 2. Equal volumes of gases arc stated to contain the same number of molecules at the same temperature and pressure, regardless of composition. 3. Unfortunately, it's not always that the young have great regard to their parents. 4. Particular attention must be paid to the chapter regarding the conditions of synthesis. 5. Many chcmical facts were described which had only qualitative significance with regard to molecular structure. 6. The work of Lewis was most important as regards the development of the clcctronic theory of valcncc.
Ex. 9. Translate the sentences into Russian.
a) 1. These results arc 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 clcctronic 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 molcculcs has been carried on by scientists since early times.
b) 1. Have you seen him? 2. Did you speak to her yesterday? 3.1 do not 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 H2S04 is on that shelf, bring it, please. 6. The temperature must be 2S ° C, don4 forget it. 7. They think it ncccssaiy to attend all the seminars. 8. The teacher made it clear that the examination will be difficult to pass. 9. Avogadro's principle let one calculatc the number of molcculcs per gram mole of a gas. 10. Chcmistiy helps one to understand other fields of scicncc better. 11. The properties of HC1 make it a useful laboratory reagent. 12. Consideration of all the facts enabled us to draw a very important conclusion. 13. They do not think it possible to work with this substancc, it is not pure enough.
Ex. 10. Translate the sentences into English.
1. Проблема структури молекули давно цікавила хіміків.
2. Структурна формула - це формула, яка показує, як оруппіровани елементи і як розподіляються зв'язку в молекулі.
3. Бутлеров був першим з російських вчених, хто написав структурну формулу. 4. У XIX столітті валентну зв'язок представляли лінією, яку проводили між символами двох хімічних елементів. 5. Природа связсй тоді була зовсім невідома. 6. При вивченні структури молекул було відкрито існування ізомерії.
7. Ізомери - це з'єднання, які мають одну і ту ж молекулярну формулу, але різні структури.
Ex. 11. Answer the following questions:
1. What methods were used in the first investigations of the structure of molcculcs? 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?
Упр. 1. Назвіть значення наступних інтернаціональних слів:
diffraction, magnetic, dipolc, moment, interpretation, resonance, entropy, information, configuration, quantum, mechanics, anticipate, discussion
Упр. 2. Визначте значення виділених слів з контексту.
1. Properties of an element are due to the composition and structure of its atom. 2. Our laboratory is provided with all the necessary chemicals and devices. 3. It is not always easy to give a complete characteristic of a compound. A. X-rays arc sometimes callcd Rontgcn rays. 5. In a molecular spectrum a scries of rather broad bands is formed, that is why it is called band spectrum. 6. It is necessary to take into account the unusual properties of the compound.
Слова до тексту:
with respect to - щодо чого-л .; wave - хвиля; nuclear - ядерний; refinement - удосконалення; disperse - розсіювати; veil - покрив, завіса; mystery-таємниця; shroud - огортати
Text 19 В
Прочитайте текст про себе (контрольний час читання - 3 хвилини). 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.
Упр. 3. Передайте основний зміст тексту в декількох реченнях.
Упр. 4. Складіть план тексту.
Упр. 5. Прочитайте пропозиції і скажіть, чи відповідають вони змісту тексту. Якщо немає, виправте їх.
1. Structural chcmistry has not changed since the 19th century. 2. The pictures of molcculcs presented by modern chcmistry and classical structural chcmistry arc not the same. 3. Electronic structures arc investigated only by chcmical methods. 4. The development of the thcoiy of quantum mechanics affcctcd the refinement of the clcctronic theory. 5. A concept of resonance was introduced in terms of the theory of quantum mechanics. 6. Application of quantum mechanics enabled scientists to develop a method for the calculation of the properties of simple molcculcs.
Упр. б. Знайдіть в тексті опис відмінностей між сучасною * структурної хімією і класичної та переведіть ці пропозиції на російську мову.
Ex. 1. Respond to the following, using the expressions: to do smth (ito work, to study, to make observations, etc.) under smb (Prof. N, Dr. A, etc.).
1. The laboratory is now an important scientific ccntrc, who is the head of it? 2. He says he has a very good scicntific adviser, under whom docs he study? 3. He has written a very good article, whom did he consult? 4.1 know diat he docs physics at Moscow University, who is his supervisor? 5. You should consult your tcachcr before making observations, who is your tcachcr? 6. This book is rather difficult but very useful for your work, who advised you to read it? 7. Your brother obtained his degree last year, who was his scientific adviser?
Ex. 2. Translate the sentences into English.
1. Я виконав цю роботу під керівництвом професора N. 2. сту дснчсскос наукове товариство працює під керівництвом доктора N. 3. Група, якою керує доктор N, нещодавно опублікувала дуже цікаву статтю про своїх останніх дослідженнях. 4. Під чиїм керівництвом ви проходите практику? 5. Ми займаємося в лабораторії якісного аналізу під керівництвом N. б. Моя подруга виконує свою курсову роботу під керівництвом N, їй дуже подобається працювати з ним. 7. Я не знаю, під чиїм керівництвом ми будемо працювати в наступному навчальному році.
Ex. 3. Make up short dialogues according to the model.
Model: - A question.
- An answer. (+, -)
- A request.
Example: - Are you going to the dean's office today?
- 1 think so.
- Could you give my application to the secretary?
Ex. 4. Give detailed answers to the following questions:
1. What can you say about the early studies concerning the structure of molcculcs? 2. What important discoveries were made in the course of structural investigations? 3. In what way was the valence bond understood in the 19th ccntury? 4. What investigations laid the foundation of the modern electronic theory? 5. What methods were used to study the structure of molcculcs?
Ex. 5. Discuss the following topics:
1. The Contribution of the Great Scientists of the Nineteenth Ccntury to the Structural Theory.
2. The Methods Used in Structural Investigations.
3. The Refinement of the Electronic Theory of Valcnce.
WHAT IS IT?
The combining power of an atom, equal to the number of hydrogen atoms which an atom will combine writh or replace.
Text 9 В | Fluorine | Lesson 10 | Text 10 В | Lesson 11 | Fascinating Phosphorus | Modifications of Phosphorus | Lesson 12 | Chemical Symbols for Representing Compounds | Weight of У12 atom of carbon 12 |