Text 14

( - 3 ). The Atomic Theory of Democritus and Dalton

The Greek philosopher Democritus (about 460-370 B.C.) who had adopted some of his ideas from earlier philosophers, stated that the Universe is composed of void (vacuum) and atoms. The atoms were considered to be everlasting and indivisible - absolutely small, so small that their size could not be diminished. The atoms of different substances, such as water and iron, were considered by him to be fundamentally the same, but to differ in some superficial way; atoms of water, being smooth and round, could roll over one another, whereas atoms of iron, being rough and jagged, would cling together to form a solid body. The atomic theory of Democritus

was pure speculation, and was much too general to be useful. Dalton's atomic theory, however, was a hypothesis that explained many facts in a simple and reasonable way.

Dalton stated the hypothesis that elements consist of atoms, all of the atoms of one clement being identical9, And that compounds result from the combination of atoms of two or more elements, each in definite number. In tliis way, he could give a simple explanation of the law of conservation of mass and of the law of constant proportions.

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1. The Greek philosopher Dcmocritus was the first who stated that matter is composed of atoms. 2. The atoms were considered to be small indivisible particles. 3. The atoms of different substances were considered by Dcmocritus to be different. 4. The atomic theory of Dcmocritus was not useful bccausc it was too general. 5. Dalton stated that all of the atoms of one clement were the same. 6. Dalton could not explain the law of conservation of mass.

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Section III

Ex. 1. Answer the questions. Use the verb take.

1. Do your experiments take much time? 2. Have you taken your exam in English? 3. When are you going to take your holidays? 4. Does your friend take interest in chemistry? 5. When arc you going to take your examination in mathematics? 6. Who took the first prize in swimming? 7. Arc you going to take post-graduate studies? 8. Do you take interest in modern music? 9. How long docs it usually take you to get here? 10..How long did it take you to do the exercise? 11. Do you take part in social activity? 12. Have you taken my pen? 13. When did you first think to take up chcmistry as your field?

Ex. 2. Translate the sentences into English.

1. . 2. , . 3. ³ . 4. , . 5. ? 6. ? 7. 40 .

Ex. 3. Make up short dialogues according to the model.

Model: - A special question. - An answer.


1) - What is it?
It is a book.
2) - When did you comc '
- At 5 o'clock.

Ex. 4. Give detailed answers to the questions.

1. In what way did the idea of ??the atom change in the course of history? 2. What scientist stimulated the development of the atomic theory? 3. What do you know about the atomic structure?

Ex. 5. Discuss the following topics:

1. Early Atomic Theories.

2. The Present Ideas about the Structure of Matter.

3. The Most Important Discoveries Concerning the Atomic Structure.


The smallest unit of an clement that can take part in a chemical change.

Text 9 | Fluorine | Lesson 10 | Text 10 | Lesson 11 | Fascinating Phosphorus | Modifications of Phosphorus | Lesson 12 | Chemical Symbols for Representing Compounds | Weight of 12 atom of carbon 12 |

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