Give the English equivalents for the following words and word combinations.
UNIT II
THE HISTORY OF THE PERIODIC TABLE
Section I
Many innovators have developed periodic tables which display chemical elements differently from the well-known Mendeleev's periodic table. Several have been devised purely for didactic reasons, as not all correlations between the chemical elements are effectively captured by the standard periodic table. Nevertheless Mendeleev's periodic table is still considered one of the most important tools in chemistry.
WARMING-UP
What do you know about the periodic table of Mendeleev?
Do you consider it helpful for chemists?
Do you know any other variations of the periodic table?
What important information on newly discovered elements can you give?
Complete the chart and share your ideas with your fellow students.
| THE PERIODIC TABLE |
| groups |
| elements |
| properties |
| D.I. Mendeleev |
TEXT A
Memorize the meaning of the following words and word combinations.
| accept, add, application, cause, close, compound, concern, contain, entirely, increase, inverse, investigation, lead, mixture, noble, occur, propose, recognize, relation, resemble, respectively, revise, search, significance, striking, success, thorough, vacant, value, weight |
Practise your pronunciation.
Valence, column, helium, neon, argon, krypton, xenon, cobalt, nickel, tellurium, iodine, protactinium, thorium, scandium, gallium, germanium, isotope.
Make pairs of the words and word combinations in column A and those in column B and make up the sentences with them.
| A | B | ||
| 1. | striking | a) | table |
| 2. | vacant | b) | values |
| 3. | noble | c) | application |
| 4. | atomic | d) | elements |
| 5. | radioactive | e) | significance |
| 6. | periodic | f) | weight |
| 7. | revised | g) | substances |
| 8. | pairs of | h) | place |
| 9. | little | i) | properties |
| 10. | predicted | j) | gases |
Read and translate the text.
THE HISTORY OF THE PERIODIC TABLE
The Russian chemist Dmitry Ivanovich Mendeleev (1834-1907) made a thorough study of the relation between the atomic weights of the elements and their physical and chemical properties, with special attention to valence. This was the final and most important step in the development of the periodic table. In 1869 Mendeleev proposed a periodic table containing seventeen columns, resembling in a general way the present periodic table without the noble gases. In 1871 Mendeleev revised this table and placed a number of elements in different positions, corresponding to revised values of their atomic weights.
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Chemists added the "zero" group to the periodic table after the discovery of helium, neon, argon, krypton and xenon by Lord Rayleigh and Sir William Ramsay in 1894 and the following years.
After its proposal by Mendeleev chemical society immediately accepted the periodic law because of its success in making predictions with its use which they verified afterward by experiment. In 1871 Mendeleev found that by changing seventeen elements from the positions indicated by the atomic weights, which chemists had accepted for them, into new positions their properties could be better correlated with the properties of the other elements.
Most of the elements occur in the periodic table in the order of increasing atomic weights. There still remain, however, four pairs of elements in the inverted order of atomic weight; argon and potassium (the atomic numbers of argon and potassium are 18 and 19, respectively, whereas their atomic weights are 39.948 and 39.098), cobalt and nickel, tellurium and iodine, and protactinium and thorium. The nature of the isotopes of these elements is such that the atomic weight of the naturally occurring mixture of isotopes is greater for the element of the lower atomic number in each of these pairs than for the element of higher atomic number; thus, argon consists almost entirely (99.6%) of the isotope with mass number 40 (18 protons, 22 neutrons), whereas potassium consists largely (93.4%) of the isotope with mass number 39 (19 protons, 20 neutrons). This inversion of the order in the periodic system, as indicated by the chemical properties of the elements, from that of atomic weight caused much concern before the atomic numbers of the elements were discovered, but now chemists have recognized it as having little significance.
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Mendeleev made a very striking application of the periodic law. He predicted the existence of six elements, which scientists had not yet discovered, corresponding to vacant places in his table. Soon chemists discovered three of these elements and named them scandium, gallium, and germanium by their discoverers. They also found that the properties of the elements and their compounds are very close to those predicted by Mendeleev.
After the discovery of helium and argon, the existence of which the periodic law had clearly indicated, the search for neon, krypton, xenon, and radon in air led to the discovery of the first three of them. Then they discovered radon during the investigation of the properties of radium and other radioactive substances.
Give the English equivalents for the following words and word combinations.
Наиболее важный шаг, периодическая таблица, отношение, атомный вес, между, особое внимание, содержать, инертный газ, пересмотреть таблицу, ряд элементов, нулевая группа, добавить к чему-л., успех, большинство элементов, в обратном порядке, атомный номер, смесь изотопов, состоять из, главным образом, большое значение, применение, свободные места в таблице, таким образом, вскоре, химическое соединение, в воздухе, привести к.
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