1. Dmitri Mendeleev developed the concept of the periodic repetition of properties. 2. There are 8 columns in the periodic table. In each column, elements are arranged by the same properties, such as the same orbital arrangement of electrons. 3. Mendeleev predicted properties of yet undiscovered (missing) elements and left empty spaces for them in the table. 4. There are natural groupings between the elements that are closely related to each other. 5. In order to understand better these natural groupings, chemists have tried to fit the elements into a single plan. 6. John Ncwlands made one of the first attempts to fit the relationships among the elements by suggesting the Law of Octaves.
1. The sun has not risen yet, but the sky in the east is getting lighter every minute.
2. I saw you walking along the street the other day with a heavy bag.
3. I have not read the newspaper today.
4. It is very late, and trams have stopped running: we must find a taxi to get home.
5. How many times have you been to St. Petersburg?
6. At last I have translated this article: now I shall have a little rest.
7. We went to the country yesterday, but the rain spoilt all the pleasure.
8. My watch was going in the morning, but now it has stopped.
9. The lecture has not begun yet and the students are talking in the classroom.
10. She has just gone out.
11. She left the room a moment ago.
12. We have not solved the problem yet.
13. When did it all happen?
14. The morning was cold and rainy, but since ten o'clock the weather has changed and now the sun is shining brightly.
15. Show me the dress which you have made.
16. Oh, how dark it is! A large black cloud has covered the sky. I think it will start raining in a few minutes.
17. Oh, close the window! Look, all my papers have fallen on the floor because of the wind.
18. When did you open the window? — I opened it ten minutes ago
Удачи в учёбе!)
2. There are 8 columns in the periodic table. In each column, elements are arranged by the same properties, such as the same orbital arrangement of electrons.
3. Mendeleev predicted properties of yet undiscovered (missing) elements and left empty spaces for them in the table.
4. There are natural groupings between the elements that are closely related to each other.
5. In order to understand better these natural groupings, chemists have tried to fit the elements into a single plan.
6. John Ncwlands made one of the first attempts to fit the relationships among the elements by suggesting the Law of Octaves.