Практикалық сабақтарының тақырыптары мен мазмұны Practical assignment №1
жүктеу/скачать 64,23 Kb.
|
chemistry (1)
- Бұл бет үшін навигация:
- VI. Read and translate the text
| II. True or false?
1) Symbols and formulas are used to indicate chemical reactions. 2) Groups of symbols are called equations. 3) Groups of symbols are called formulas. 4) There are 102 chemical elements now. 5) The more electropositive element is always designated last in the formula. 6) Subscriptions are used to designate the number of atoms of each element present in the molecule. 7) Mendeleyev made his discovery in 1879. 8) There were several vacant spaces in Mendeleyev’s table which led him to predict the existence of six undiscovered elements. 9) The table wasn’t modified. 10) Properties of the elements are periodic functions of the nuclear charges of their atoms. VI. Read and translate the text Man at last understood the elements well enough to make his own. First there were some elements still missing from the Periodic Table. The fact was they were practically missing from nature, too. Scientists had to make these elements themselves. To make such elements meant first of all to carry on great experimental work. Many scientists worked hard at this problem. In 1919 Ernest Rutherford was the first to change nitrogen to oxygen by bombarding nitrogen atoms with alpha-particles. To alter an element artificially is to add or subtract particles in its nucleus. The first completely new man-made isotope was created by Rutherford's method, its creators being Irene Curie and her husband Frederic Joliot. To do that they had to bombard aluminium with alpha-particles. This attack transformed some of the aluminium atoms into a highly radioactive substance. This substance was a new kind of phosphorus, its atomic weight being 30, instead of natural phosphorus 31. It was no wonder that phosphorus 30 did not occur in nature, its half-life being only two and a half minutes. Thus the Joliot-Curies were the first to produce "artificial radioactivity". The era of artificial transmutation began with the building of the first "atomsmasher", i.e. the cyclotron. By means of cyclotron and energetic particleaccelerators developed later it became possible to open up the nucleus of any atom. It became possible to add particles to it, and even to create new ones. The first element produced in this way was the missing number 43, it being named "technetium" meaning "artificial". The aim of the scientists was to discover other elements. In 1939 a new element was found. It behaved like an alkalimetal, therefore it was to be 87 the missing number of the alkali-metal family. It was called "francium". It was detected in nature. Later that element was produced artificially by an accelerator, and only then did chemists obtain enough of it. For that reason francium is to be considered as a manmade element. Later scientists discovered traces of an element in neutron-bombarded uranium. They called it "neptunium". Radioactive neptunium gave rise to another element —number 94. In 1955 chemists could produce a few atoms of element 101 which was named"mendelevium" in honour of D. I. Mendeleyev. The isolation of element number 102 occurred in 1963, it being named "nobelium", as part of the work was done at the Nobel Institute in Stockholm. жүктеу/скачать 64,23 Kb. Достарыңызбен бөлісу:
|