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1. No commercial applications of indium were attempted for many years. 2. Their attempt to obtain pure indium was a success. 3. The available supply of indium at that time was only one gram. 4. Some compounds of indium were supplied for further analysis. 5. In(OH)3 is precipitated from an indium salt solution. 6. When KOH was added to an indium salt solution, a precipitate of In(OH)3 was formed.
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1. Hydrogen atom contains only one electron and one proton. 2. Red phosphorus is more stable than the white one. 3. An element is a substance which consists of only one kind of atoms. 4. The salts formed by hydrochloric acid are called chlorides, the ones formed by sulphuric acid are called sulphides. 5. Chlorine exists in two isotopic forms: the one has the atomic weight of 35 and the other of 37. 6. Phosphorus is one of the elements of Group V. 7. Reactions of dilute acids and the concentrated ones are not alike. 8. Phosphorus exists in several allotropic modifications, yellow and red are the most common ones. 9. The chemical properties of ozone are similar to those of oxygen, but one must point out that ozone is more chemically active. 10. Phosphorus is readily dissolved in carbon disulphide, one part of it will dissolve nine parts of phosphorus. 11. This modern apparatus gives more accurate results than the old one and it is much easier to handle.
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1 .Do it as quickly as you can. 2. Do you know when the periodic law was stated? 3. I can't do it now, I must be going. 4. The alchemists did improve techniques during their search of the philosopher's stone and an elixir of life. 5. They do synthesize new materials in their laboratory. 6. Scientists did not understand organic chemistry before the synthesis of urea. 7. He will have done it by 5 o'clock.
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Text 20 A
The Structure of Covalent Compounds
The electronic structure of molecules of covalent compounds involving. the principal groups of the periodic table can usually be written by counting the number of valence electrons in the molecule and then distributing the valence electrons as "unshared electron pairs and shared electron pairs in such a way that each atom achieves,an argonic structure.
For many molecules the covalence of each atom is equal to the number of unpaired electrons in its outer shell, and is, thus, simply related to the position of the element in the periodic table. For other molecules and ions the covalence of the atoms is less simply related to the periodic table.
It is often necessary to have some experimental information about the way in which the atoms are bonded together. Thus, there are two compounds with the composition 2: ethyl alcohol and dimethyl ether. The chemical properties of these two substances show one of them, ethyl alcohol, to contain one hydrogen atom attached to an oxygen atom, whereas dimethyl ether doesn't contain such a hydroxyl group.
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The atoms of most molecules are held tightly together by a very important sort of bond, the
shared-electron-pair bond or the covalent bond. This bond is so important, so nearly universally present in substance that Professor Gilbert Newton Lewis of the University of California (1876 1946), who discovered its electronic structure, called it the chemical bond.
It is the covalent bond that is represented by a dash in the valence-bond formulas, such as
that have been written by chemists for over a hundred years.
Modern chemistry has been greatly simplified through the development of the theory of the covalent bond. It is now easier to understand and to remember chemical facts, by connecting them with our knowledge of the nature of the chemical bond and the electronic structure of molecules, than was possible at the beginning of the century.
Words and Word-Combinations to Be Memorized
achieve, argon, such a,, connect, ether, ethyl, experimental, greatly, information, nearly, professt>r, simplify, sort, universally, university, covalent, in such a way, in this way
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1. . 2. . 3. . 4. () . 5. In (OH) 3 . 6. KOH , In (OH) 3 .
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1. . 2. , . 3. - , . 4. , , . 5. : 35, - 37. 6. 5 7. . 8. , , . 9. , , . 10. , . 11. , , .
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1. , . 2. , ? 3. , . 4. . 5. . 6. . 7 5 .
