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Text A

The atom and its nucleus

Most people are familiar with1 the idea that the chemical elements which constitute the matter of the universe are made up of particles called atoms and that an atom is the smallest recognizable particle of an element. These atoms are extremely small; it is impossible to convey an idea of their size in any ordinary simple terms. One can say that they are about a hundred millionth part of a centimetre in diameter or, put another way, questionable whether these expression convey much to anyone who is unaccustomed to scientific measurements.

For long the atom was considered indivisible; actually, this is the meaning of the Greek word the name is derived from (atomos – indivisible). During the last sixty years, however, it has been shown that this idea is untrue and that the atom is itself a complicated structure of very much smaller constituent particles the total volume of which is only a very small part of the total volume of the atom.

These ideas have led to the present conception of the general structure of the atom, that it consists of a kind of solar system in which particles called electrons play the part of planets and move in orbits round a central sun called the nucleus.

The electrons are extremely light and each carries a negative charge of electricity. The nucleus, on the other hand, is very heavy compared with the electrons; actually, the whole mass of the atom is concentrated in it. The nucleus carries a positive electrical charge which is of greatest importance as it determines the chemical nature of the atom. In a normal atom the total of all the charges on the planetary electrons is equal to the charge on the nucleus, so that the atom is electrically neutra.

The nucleus is itself made up of elementary particles of which there are two principal sorts: protons and neutrons.

Proton is the basic particle of all atomic nuclei. It has a single positive charge equal to that of an electron which is negative.

It is a comparatively heavy particle. Neutron is a particle which is present in all nuclei except hydrogen. It has a mass slightly larger than that of a proton, but no charge, either positive or negative, a property which allows it, when free, to penetrate all nuclei. All substances on the earth as well as out of it whether gaseous, liquid or solid, are made up of atoms.

Grammar and lexical exersices

I. Translate the following sentences into Ukrainian paying attention to the Modal Verbs.

1. You should carry out this experiment using the technique developed in our laboratory. 2. Everyone must do his duty. 3.I have to do some extra work now because one of my colleagues is having a holiday and I have taken over his part of our joint research. 4. We can carry out this experiment now because we have all the necessary equipment. Last year we did not have it and therefore could not do the job. 5. May I take your pen for a minute? — Yes, of course, you may.

II. Translate the following sentences into Ukrainian paying attention to the meaning "shall, should, will, would, to be, to have".

1.I shall take my examinations in June. 2. They shall improve their method of work, if they want to obtain better results. 3. This new car will be tested tomorrow. 4.I will replace the old parts of the car. 5. You should do it by all means. 6. If I had read yesterday's news-paper, I should have learned about the accident. 7. They knew that I should fly to London. 8.I would not change my plans. 9. If he had not made a mistake in the calculations, the bridge would not have collapsed. 10. She said she would be delayed at the institute. 11. He would sit for hours on the shore and look at the water. 12. The plant was far away from the city. 13. The channel was deepened. 14. He was travelling in the north. 15. He was to come at 5.16. They have a good plan. 17. They have already passed their exams. 18. They had to test the engine twice.

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