М. М. Кутепова The World of Chemistry Мир

Listen to a short talk about one of the chemical discoveries and choose its title out of the given ones.

1. 
   Chemical Reactions.
   
2. 
   Small Changes.
   
3. 
   The Atomic Theory.
   
4. 
   Chemical Observations.
   

Good morning! I’m Gean Umland from the University of Huston. I was asked by your Chemistry Faculty Dean to make a short presentation of an extract from my General Chemistry Textbook published recently. I’m going to speak about John Dalton’s contribution.
Well, I’ll start by saying that the modern atomic theory was suggested by an English schoolteacher, John Dalton, in 1803-1809. Dalton saw that the existence of atoms would explain the law of constant composition. Do you remember it? Yes, quite right. In a pure compound the percent (by weight) of each element is always the same. Atoms’ existence could explain other observations that had been made about chemical reactions. However, the scientific establishment of that day was unwilling to approve of the new idea. Can you imagine, that more than 50 years had passed before the atomic theory was generally accepted?! Isn’t it incredible that even as late as 1900 the author of one General Chemistry textbook refused to mention Dalton’s theory?! We see that today the main ideas of his theory are still used, though, I should say, the discovery of new facts has made a few changes necessary.
Now let’s summarize the main points of Dalton’s theory.
First, all matter is composed of atoms. What is an atom? It’s the smallest particle of an element that takes part in chemical react ions.
Second, all atoms of a given element are alike. What does this mean? Good. It means that all atoms of gold, for instance, are the


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same. Atoms of different elements are different. Can you give us an example? That’s it. An atom of copper is lighter than an atom of gold.
Third, compounds... what are compounds? You’re quite right. They are combinations of atoms of more than one element. And the relative number of each type of atom is always the same. Any examples? How smart you are! Yes, in water there are always two hydrogen atoms for each atom of oxygen.
Now, can atoms be created or destroyed? No, definitely not. And atoms of one element can’t be changed into atoms of another element by chemical reactions.
1 think, that’s all that I wanted to speak about today. Thank you. Do you have any questions?

8. 
   Listen to the lecture again and 1) write out the statements which the speaker uses to address the students; 2) change the questions from direct into indirect speech using the expressions from Unit 1 (ex. 10); 3) change the statements expressing Dr. Umland’s approval of the students⁹ answers into indirect speech. You are given two examples:
   

Example 1: Do you have any questions?
I’d like to know if you have any questions.
Example 2: Good morning!
Dr. Umland greets the students.

9.