Many compound substanccs do not have particularly high melting and boiling points, do not conduct electricity when they arc molten, and, thus, give no indication of being ionic. The particlcs of such compounds arc molecules. In these, any bond between two atoms is believed to be a pair of shared electrons, as it was suggested originally by the American chcmist G. N. Lewis. The electrons of such a shared pair occupy a single orbital and spin in opposite directions. Atoms entering such unions arc said to cxibit covalcncc and the bonds thus formed arc described as covalcnt.
""" When two or more atoms share electrons to form molcculcs, all the electrons of the several atoms involved[7] become common property and arc distributed among energy levels and orbitals characteristic of the molecules. A simpler treatment than this method of molecular orbitals is that of atomic orbitals. By it, cach atom in the molcculc is treated as if it controlled all its own electrons cxccpt those shared with another atom. The shared electrons arc treated as common to both.
The carbon-atom has two electrons in its first main energy level and four in its second. To obtain a noble-gas configuration it would have to loose or gain 4 electrons. Since it can do neither, it approaches the desired goal as nearly as possible by sharing its 4 electrons with atoms that also seek greater stability and will, in turn, share some of their valence electrons with it.
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. Not all compound substanccs conduct electricity when they arc molten. 2. Lewis studied the bond formed by a pair of shared electrons. 3. The bond is described as covalcnt if the electrons of a shared pair occupy a single orbital and spin in opposite directions. 4. The method of atomic orbitals is more complcx than that of molecular orbitals. 5. The shared electrons arc believed to belong to one of the two bounded atoms. 6. To obtain a noble-gas configuration the carbon atom has to loose 4 electrons.
Упр. б. Найдите в тексте описание того, кар распределяются электроны при образовании связи с участием углеродного атома, и переведите этот отрывок на русский язык.
Section III
Ex. 1. Respond to the following using the verbs to say, to speak, to tell, to talk:
1. Do you speak German? 2. Can you speak louder? 3. He said, I was right, didn't he? 4. Don't say anything, if you arc not sure. 5. Tell her that she should comc at 10 o'clock, please. 6. He told mc that there were too many mistakes in my paper. 7. They talked all the evening, but I didn't take part in their conversation. 8. You were talking to Dr. N when I met you, what did you tell him?
Ex. 2. Translate the sentences into English.
1. Наш преподаватель часто говорит, что мы мало читаем. 2. Он говорит нам, что надо читать новые журналы. 3. Скажите, почему вы не пришли вчера? 4. Они говорили о методе измерений, когда я подошел. 5. Говорите громче, пожалуйста. 6. Он не любит говорить о своих планах. 7. На каком иностранном языке вы говорите? 8. Скажите мне, коша закончите. 9. Он говорит, что этот материал очень труден. 10. Она сказала, что сегодня нс готова отвечать.
Ex. 3. Make up short dialogues according to the model.
Model: — A statement.
— A question.
| Example: |
— A statement.
— I haven if prepared my homework today.
— Haven t you traslated the text?
— I've only looked it through.
Ex. 4. Give detailed answers to the following questions:
1. What electrons take part in forming bonds between atoms? 2. What kind of bonding is called a covalent bond? 3. What is the relationship between the activity of the molcculc and its structure? 4. What do modern chemists think about the phenomenon of covalcncc?
Ex. 5. Discuss the following topics:
1. The Structure of Covalent Compounds.
2. The Kinds of Bonds Between the Atoms.
3. An Example of a Covalent Compound.
WHAT IS IT?
A way of holding component atoms togcdicr in a single molcculc characterized by the sharing of electrons.