The periodic table of d.I. Mendeleyev

There are certain natural groupings among the chemical elements in which every element is closely related to the other elements in its group. In order to understand better these groupings, chemists have tried to fit the elements into a single plan. One of the earlier attempts to fit the relationships among the elements into a single law was made by John Newlands in England, who suggested the Law of Octaves. This concept of the periodic repetition of properties was further developed by a Russian chemist Dmitri Mendeleyev who created a Periodic Table in which he arranged the elements according to their atomic weights and corresponding chemical properties. D.I. Mendeleyev listed the elements known at the time (1869) in the order of their atomic weights from the lightest to the heaviest. The elements were arranged in a table of eight columns; elements having similar properties appeared in the same columns or groups in the table. Mendeleyev even predicted that there were undiscovered elements and left empty spaces in this table for the new discoveries.

There are many ways the Periodic Table can be used. The table can be used to find the atomic number. The atomic weight is also indicated in the table. The orbital arrangement of electrons is shown for each of the elements. The common oxidation states are given. For most elements these numbers are the same as the valence numbers. The table enables us to recognize6 families of elements. For example, copper (29), silver (47), and gold (79) will all be found in the same column. They have similar properties and are considered a chemical family. And at last the table can be used to predict the properties of the elements. The fact that the Periodic Table can assist in predicting properties of elements has helped in the discovery of missing elements.

Vocabulary

arrange – розташовувати list - перелічувати assist - сприяти predict - передбачати certain - визначений relate – зв’язувати closely - близько

repetition - повторення common - загальний show - демонструвати concept - концепція, поняття single - одиничний indicate - вказувати suggest - припускати

Exercises

1. Answer the questions

1. What certain natural groupings are there among the chemical elements?

2. What have chemists tried to do in order to understand better these groupings?

3. Who made one of the first attempts to fit the relationships among the elements?

4. Who developed the concept of the periodic repetition of properties?

5. What columns are there in the Periodic Table?

6. What did Mendeleyev predict?

7. What are the ways the Periodic Table can be used?

2. Read and translate the text with vocabulary Joseph Priestley

A very famous British scientist of the18^th century was Dr Joseph Priestley (1733-1804). He was a minister in the government but won a high reputation for his scientific work. One day in 1774 he was experimenting with a large burning-glass which had just been presented to him. Among the substances he heated with it was the red oxide of mercury. He knew that this oxide would be made by heating mercury, so it is not likely that he expected to obtain anything from further heating of the oxide, but if this was so, then he must have been very surprised. The oxide, after darkening in colour, eventually turned into mercury again, and a gas was given off. Priestley tested this gas and found that it would: a) allow substances to burn in it much more brilliantly than in air; b) support life. He was puzzled as to its nature, but as substances burned in it more brightly than in air he considered it to be a purer form of air. It was, in fact, the gas we now call oxygen.