6. Complete the following sentences by adding a clause:

1. Mendeleyev declared that …

2. He said that elements ...

3. Scientists discovered that …

4. He declared that the table …

5. The reporter mentioned that …

6. One notes that …

7. Complete the following sentences by adding the clauses:

1. An advantage may be gained if ...

2. Two points of historical interest may be mentioned while …

3. The nature of the electron cloud is very important, because …

4. Elements to the right of this line are not metals although ...

8. Read the sentences and say whether they are true or false.

1. This table was made by the Russian chemist Mendeleyev about 1870.

2. This table shows the known elements in the order of the strength of the electrical charge on their nuclei, or inner portions.

3. All elements in the table are found in nature.

4. Elements to the left of the heavy, stepped line near the right of the table are non-metals.

5. The names of the recently discovered metals end in “-ium”.

9. Answer the following questions:

1. What does the periodic table show?

2. How are the elements in the table placed?

3. Are the elements in the same column are similar chemically?

4. How many elements shown in the table are found in nature?

5. What does the nature of the electron cloud show?

6. What historical points must be mentioned while searching the table?

7. Why were produced artificial elements?

8. Can one quickly determine from the table whether the element is a metal or a non-metal?

Section 3

1. Read and translate the following text: some interesting relationships

A study of the periodic table reveals that the position of an element in the table may give an indication of its properties. One of the most striking examples is that all- or nearly all of the elements in the first ten columns have positive magnetic susceptibilities that are they are paramagnetic. On the other hand, all elements in columns to the right of the tenth, with the exception of oxygen, have negative magnetic susceptibilities, or are diamagnetic. Furthermore, the metals that are ferry magnetic, that is are magnetic in the sense that iron is, all lie in the same horizontal line. There are three of them: iron, nickel, and cobalt: elements 26, 27, and 28, respectively. Another interesting fact is that metals in the same column of the periodic table often have similar chemical and physical properties. For example, the three metals of highest electrical conductivity, copper, silver, and gold, all lie in column 11. The three metals in column 4 have the property of absorbing astonishing amounts of oxygen and nitrogen at relatively low temperatures. Even a moderate amount of absorbed gas makes them very brittle although their external appearance may give no indication of their changed condition. This brittleness caused considerable trouble when production was undertaken and required special procedures for melting and hot fabrication. The precious metals, not including silver and gold, lie in a group that includes elements 44, 45, 46, 76, 77, and 78.

No mention has yet been made of the two rows in the lower part. These two series of elements usually are called the “rare earths”. The upper one is called the lanthanide series because it fits in the periodic table immediately alter lanthanum. Frequently lanthanum is included in this group because of some chemical similarity and as a convenience in description. These elements have such close chemical similarities that separation of some of them has been difficult. Most of the actinide series, lower strip, show radioactivity. The lower row has been named the actinide series because it follows immediately after actinium.