Chemical elements and compounds

A chemical element is a substance that cannot by any ordinary means 1 separated into two or more different substances. This definition does not exclude the possibility of decomposing an element into others by radioactive or similar agencies.

Chemical compounds are pure substances which can, by ordinary chemical means, be separated or decomposed into different elements, or which can be made by combining different elements. The molecules of a compound are regarded as aggregates of smaller particles of the elements, known as atoms, in| which the compound can be broken up.

The atoms are regarded as smallest mass elements which occur separately in the structure of the molecules of either compounds or elementary substances, so far as can be determined by ordinary chemical means. The mole of an element consists of a definite (usually small) number of its atoms, molecule of a compound consists of one or more atoms of each of its several elements, and the numbers of the various kinds of atoms and their arrangement are definite and fixed, they determine the character of a compound.

Ex. I. Work in pairs.

Find out: when this reaction occurred.

Pattern: St. A: When did this reaction occur?

St. B: It occurred an hour ago, etc.

1. when the term "organic chemistry" originated; 2. what this term was associated with; 3. when living organisms gathered some minerals; 4. how the minerals were gathered; (change roles) 5. what hydrocarbons are composed of; 6.what molecules hydrocarbons include; 7. what position hydrogen atoms occupy in a methane molecules; 8. why this molecule is called three-dimensional.

Еx. II. Translate the following sentences paying attention to the words in I type:

L The term "organic compounds" is no longer associated with the origins of the substances. 2, The term of office of American presidents is 4 years. 3.When she was in her second year she wrote two term-papers in chemistry. 4. There are two terms in each academic year at the Institute. 5. Under the terms of contract the firm will pay the money this year. 6. This substance was obtained by means of heating. 7. There are different means of transport in Moscow 8. As he was fatherless and had no means for existence he began to work early. 9. The word "means" means "средства", "способ". 10.1 don't understand you. What do you mean by saying it? 11. Money means nothing to him.

Ex. III. Correct the following wrong statements in not less than 3 sentences:

1. Organic chemistry is the chemistry of non-carbon compounds.

2. Compounds derived from living matter are called inorganic compounds.

3. Sodium, phosphate, calcium are the examples of organic materials.

Ex. IV. See whether the following chemical reactions are possible and if not, explain why:

1.2CO+O₂=2CO₂

2.Fe2O₃ + 3CO = Fe + 3CO₂

3.H₂CC1₂

Read and translate the text

Organic compounds

Organic chemistry is an ancient term. It goes back to the time when it

was believed that certain compounds could occur only in living organisms (hence the name "organic").

It was discovered at an early date that the element carbon is of the great­est importance in these "organic" compounds and what now is called organic chemistry is the chemistry of carbon compounds. About four fifths of all known compounds contain carbon and only one fifth other elements but no carbon.

The property of carbon which lies at the root of its amazing preponder­ance¹ in compounds is the ability of carbon atoms to be linked to each other. This phenomenon is not unknown in inorganic chemistry. But carbon goes far beyond anything known of other elements in this respect. Compounds exist which con­tain a thousand and more carbon atoms tied to each other in a long chain.

The possibility of forming new compounds by adding more and more carbon atoms to a chain is only one reason for the great number of organic com­pounds. Another is the possibility of different arrangements of a given number of carbon atoms in a molecule.

Many other elements can form compounds with carbon, the most important ones being hydrogen, oxygen, nitrogen , sulphur . Among the organic compounds those containing only hydrogen and carbon, the so-called hydrocarbon are the least reactive. They are also more numerous than all others.

Ex. 1. Point out which of these sentences contains the information from text .

1. Living materials have some inorganic constituents, such as sodium ions, phosphate ions, calcium ions, etc.

2. One of the most important properties of carbon is the ability of carbon atoms to be linked to each other.

3. The hydrocarbons, which are organic compounds, are composed of carbon and hydrogen.

Ex. 2. Rearrange the sentences to make a short summary of the text, 'since 'or'as' wherever possible:

1. Carbon atoms have the ability to be linked to each other.

2. About four fifths of all known compounds contain carbon.

3. Organic chemistry is the chemistry of carbon compounds.

4. This property and the possibility of different arrangements of a give,, number of carbon atoms in a molecule explain the amazing preponderance of carbon in compounds.

Additional text. Read and translate.