The Atomic Structure of Matter

The most important of all chemical theories is the atomic theory. In 1805 the English chemist and physicist John Dalton (1766–1844), of Manchester, stated the hypothesis that substances consist of small particles of matter. He called these particles atoms, from the Greek word «atomos», meaning indivisible. This hypothesis gave a simple explanation or picture of previously observed but unsatisfactorily explained relations among the weights of substances taking part in chemical reactions with one another. It was necessary that the hypothesis be confirmed. Hadn't it been verified by further work in chemistry and physics it wouldn't have become the atomic theory. The existence of atoms is now accepted as a fact.

All ordinary matter consists of atoms. The exceptional kinds of matter are the elementary particles from which atoms are made (electrons, protons, neutrons) and similar sub-atomic particles (positrons, mesons). But atoms are the units which retain their identity when chemical reactions take place, and therefore they are important to us now. Atoms are the structural units of all solids, liquids, and gases. They are very small ‑ only about 2 Å to 5 Å in diameter.

This is indeed small. If a piece of rock, or anything else, one inch in diameter were magnified to the size of the earth, its constituent atoms would become about the size of golf balls or tennis balls.

Every atom consists of one nucleus and one or more electrons. The nucleus is a small, heavy particle containing almost all the mass of the atom. Nuclei are very small indeed. The nucleus of an atom is only about one ten-thousandth as great in diameter as the atom itself, and the volume of the nucleus is one million-millionth, of the volume of the atom.

If nuclei could be packed together side by side, they would give a form of matter with very great density. The electron is a particle with a small mass, 1/1845 that of the lightest nucleus, and with a negative electrical charge.

The electron itself is about as large as a nucleus, its diameter being about 10-12 cm. The electrons in an atom are attracted by the nucleus. The electrons in an atom move rapidly around in the space extending over a diameter of a few Å about the nucleus, and because they move about so fast they effectively fill this space in such a way as to repel any other atom which approaches to within this diameter.

Were it not for the rapid progress of scientific knowledge about atoms the evidence for the existence of atoms would not be so overwhelming.

Exercise 15. Give English equivalents for the following words and word combinations.

Сформулювати гіпотезу; той, що неможливо поділити; недостатньо розтлумачені; потрібно було, щоб гіпотеза була підтверджена; прийняти як факт; елементарні частинки; коли відбувається хімічна реакція; це – дійсно мало; будь-що інше; одна десятитисячна; простір, що тягнеться по діаметру у декілька ангстремів навколо ядра; ефективно заповнювати простір.

Exercise 16. Find in the text synonyms for the following words.

To name; easy; interpretation; to check; type; to contain; significant; building; tiny; volume; component; weighty; really; large; structure; to near; fast; method; advance; learning; indication; innumerable.

Exercise 17. Decide if the statements below are true or false.

1. The Greek word “atom” means invisible.

2. Atoms are the structural units of some substances.

3. Each atom consists of at least two constituents.

4. If a matter has a great density, its nuclei are packed together side by side.

5. The diameter of a nucleus is one million-millionth of the atom’s diameter.

Exercise 18. Discuss the following issues.

1. What would you do if the atomic theory were not verified yet? 2. What would you do if the hypothesis concerning the atomic structure of matter were not accepted yet by scientists? 3. What would you do if the atomic theory were unsatisfactorily explained? 4. What would you do if the relations among the weights of substances taking part in chemical reactions were only observed? 5. What would you do if you were interested in the problem of sub-atomic particles? 6. What would have happened if the hypothesis by John Dalton hadn’t been verified? 7. What would have happened if scientists hadn't been confirmed by further work in chemistry and physics? 8. What would have happened if a piece of rock had been magnified to the size of the earth? 9. What would have happened if nuclei could be packed together side by side? 10. What would have happened if the progress of scientific knowledge about atoms hadn't been so rapid?

Exercise 19. Grammar test.

1. I wish you would have called.

   1. You called.

   2. You didn’t call.

2. If I have money, I buy English books.

   1. I always do it.

   2. I do this when I have money.

3. If she had studied for her test, I’m sure she would have done quite well.

   1. She didn’t study.

   2. She studied.

4. If Mary had been at the office, she would have helped you.

   1. Mary helped you.

   2. Mary didn’t help you.

5. You could have got a higher score.

   1. You didn’t get a high score because you didn’t study.

   2. You got a high score because you studied.

6. They could have finished the project on time.

   1. They had the ability to be quicker.

   2. They finished the project on time.

7. Let’s pretend that we have this opportunity.

   1. We have the opportunity.

   2. We don’t have the opportunity.

8. I wish you had come back.

   1. You did not come.

   2. You came.

9. If you had done your homework, you would have got an excellent mark.

   1. You didn’t get an excellent mark because you didn’t do your homework.

   2. You did your homework, and so you got an excellent mark.

10. You could have taken a friend to the party.

    1. You came alone.

    2. You came with a friend.

11. I wish that you liked the meeting.

    1. You didn’t like the meeting.

    2. There is a possibility that you like the meeting.

12. I hope that you enjoyed the party.

    1. You didn’t enjoy the party.

b. There is actually possibility that you liked the party.

UNIT 4

GRAMMAR: Participle I

TEXTS: “Laser”; “Cutting through a myth about modern lasers”