2015-08-21
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| 1. Elements with similar properties are placedinthe same vertical column. 2. Mendeleyev placed elements with similar properties in the same vertical column. 3. Elements placed in the same vertical column have similar properties. | a. Элементы, помещённые в той же самой вертикальной колонке, имеют схожие свойства. b. Элементы с похожими свойствами помещены в той же самой вертикальной колонке. c. Менделеев поместил элементы с похожими свойствами в одной и той же вертикальной колонке. |
13. Choose as many words as you can of ex.1 and form sensible sentences.
For example: Special noise absorption materials are even mixed with road asphalt and coat electric power lines here.
SPECIALIST READING
Read the text “Covalent Bonds” only once. How much can you remember? Answer these questions without additional reading.
1. What do you know about the Mendeleev Periodic Table of Elements?
2. How many elements are known to science today?
3. Do you know that some elements do not exist at all in nature?
4. How do you define valence electrons?
5. What can you say about atoms in a solid piece of pure silicon?
If you failed try to answer these questions again after doing the exercises given below the text.
In the Mendeleev Periodic Table of Elements all the elements are grouped according to their chemical properties. Elements with similar properties are placed in the same vertical column.
Today more than 100 (one hundred) elements are known to science. Some of them exist in large quantities. Others such as uranium and radium are relatively rare. Some elements do not exist at all in Nature, they are created by atomic physicist using special equipment.
In each atom, having many electrons, there is a nucleus and electrons orbiting around it in several shells. The electrons of the outer shell are called valence electrons. This outer shell can hold other electrons.
For example, in the aluminium atom there are three electrons in the outer shell. The atom of this metal can easily give up these valence electrons, that is why aluminium is a conductor.
In a solid piece of pure silicon there are four valence electrons. Each valence electron orbits not only around the parent atom but also around the neighbouring atom. This bond is called a covalent bond.
