Molecules are chemical units composed of one or more atoms. The simplest molecules contain one atom each; for example, helium atoms (one atom per molecule) arc identical with helium molccules. Oxygen fenoleculcs (О?) are composed of two atoms, and ozone (O3) of three. Molecules may contain several different sorts of atoms. Water (H20) contains two different kinds, hydrogen and oxygen, and dimethyl amine ((CH^NH) has three kinds. Molecules of many common gases (hydrogen H2, oxygen O2, nitrogen N2, and chlorine С12) consist of two atoms cach.
Not all molcculcs are molecular in structure. Some are atomic and many are ionic. Molecular substances are characterized by low boiling points and poor conductivity of electricity when dissolved or melted. Gases are generally molecular, and so arc many liquids, and some solids. All compounds of hydrogen and non-metallic oxides arc molecular. These compounds are considered to be bonded by a force callcd a covalent bond (or bonds) which consists of one or more shared electron pairs.
The size of molecules, especially of the smaller ones, is so tiny that to make a meaningful comparison is rather difficult. Let us assume that the water molcculcs in a cup of water are dyed so that they can be identified. If this cup had been thrown into the ocean 2,000 years ago, these molccules would have become distributed evenly in all bodies of water on the earth.
A cup of water taken at random from your nearest supply, would give you at least one hundred of the original dyed molecules. The exceedingly large number of molcculcs of water in a cup is, of course, dircctly related to the fact that cach molcculc is exceedingly small. Molcculcs are too small to be visible in ordinary light. The most powerful and best illuminated optical microscope has failed to reveal molcculcs by dircct vision, although it is claimcd that they have been resolved in the electron microscopc.
Упр. 3. Передайте основное содержание текста в нескольких предложениях.
Упр. 4. Составьте план текста.
Упр. 5. Прочтите предложения и скажите, соответствуют ли они содержанию текста. Если нет, исправьте их.
1. Molecules usually contain several different kinds of atoms. 2. The water molecule is composed of two different sorts of atoms. 3. Molecules of all gases consist of two atoms. 4. Molecules may be molecular, atomic or ionic in structure. 5. There is no difficulty in comparing molecules by their size. 6. Molcculcs arc too small and cannot be seen by ordinary means. 7. The electron microscopc is the most powerful instrument that is used for molecular investigations.
Ex. 6. Найдите в тексте и переведите на русский язык предложения, где идет речь о молекулах, состоящих из разнородных атомов, а также предложения, в которых дается характеристика таких молекул.
Section Ш
Ex. 1. Respond to the following statements. Use the expressions: you are right; yes, indeed; probably; you are not quite right; I can V agree with you.
1.1 hear you are leaving for Moscow today. 2.1 think your work was very useful. 3.1 think it would be better to speak to him. 4. Your results don't verify your hypothesis. 5. The lecture was not veiy easy to understand. 6. Your sister has just left school, hasn't she? 7. As far as I know, Niels Bohr was not only a great physicist but a distinguished philosopher as well. 8. If I am not mistaken, you arc veiy good at sports.
Ex. 2. Translate the sentences into English.
1. Мне кажется, текст о молекулах совсем легкий. —Да, ты прав, он легче других текстов. 2. Мне говорили, что вы больны, а вы пришли на занятия.—Да, конечно, мне следует пойти домой. 3. Студенты вашей группы мало работают.—Вы не совсем правы, мы выполняем все, что необходимо. 4. В его работе много ошибок. — Не могу согласиться с вами, в его работе только одна серьезная ошибка. 5. Он скоро придет? — Вероятно. Он говорил, что придет к началу. 6. Вам надо повторить эксперимент. — Да, конечно, во вторник я сделаю всс еще раз.
Ex. 3. Make up short dialogues according to the model.
| Example: |
Model: — A disjunctive question. — An answer. (+, -)
— You are a student, aren't you?
— Yes, I am. / No, I'm not.
Ex. 4. Give detailed answers to the questions.
1. What is a molcculc? 2. What determines the properties of molecules? 3. What kind of molcculcs arc there? 4. In what way can the molcculcs be investigated? S. What is the difference between the molcculcs of elements and compounds.
Ex. 5. Discuss the following topics:
1. Kinds of Molcculcs.
2. Molecular Composition and Structure.
3. Definition of a Molecule.
WHAT IS IT?
The smallest particle of matter that has the same chcmical properties as the whole mass.