Have something done

LESSON 14.

TEXT: «Molecular Composition and Size»

Grammar: Construction” have something done”.

Reading: Joke. Dialogue.

Find out the words in the dictionary. Write them down and learn.

Read the text. Use a dictionary, if necessary.

Text. Molecular Composition and Size

Molecules are chemical units composed of one or more atoms. The simplest molecules contain one atom cach; for example, helium atoms (one atom per molecule) are identical with helium molecules. Oxygen tonoleculcs (O₂) are composed of two atoms, and ozone (O₃) of three. Molecules may contain several different sorts o f atoms. Water (H₂O ) contains two different kinds, hydrogen and oxygen, and dimethyl amine (CH₃NH) has three kinds. Molecules of many common gases (hydrogen Н₂, oxygen О₂, nitrogen N₂ , and chlorine Cl₂) consist of two atoms each.

Not all molecules are molecular in structure. Some are atomic and many are ionic. Molecular substances are characterized by low boiling points and poor conductivity of electricity when dissolved or melted. Gases are generally molecular, and so are many liquids, and some solids. All compounds of hydrogen and поп-metallic oxides are molecular. These compounds are considered to be bonded by a force called a covalcnt bond (or bonds) which consists of one or more shared electron pairs.

The size of molecules, especially of the smaller ones, is so tiny that to make a meaningful comparison is rather difficult. Let us assume that the water molecules in a cup of water are dyed so that they can be identified. If this cup had been thrown into the ocean 2,000 years ago, these molecules would have become distributed evenly in all bodies of water on the earth.USA cup of water taken at random from your nearest supply, would give you at least one hundred of the original dyed molecules. The exceedingly large number of molecules of water in a cup is, of course, directly related to the fact that each molecule is exceedingly small. Molecules are too small to be visible in ordinary light. The most powerful and best illuminated optical microscope has failed to reveal molecules by direct vision, although it is claimcd that they have been resolved in the electron microscope.

Mashq 3. Matnning asosiy tarkibini bir nechta jumlalarda ko'rsating.

Mashq 1. Matnning rejasini tuzing.

Mashq 2. Jumlalarni o'qing va matn mazmuniga mos kelishini ayting. Agar yo'q bo'lsa, ularni tuzating.

1. Molecules usually contain several different kinds of atoms. 2. The water molecule is composed of two different sorts of atoms. 3. Molecules of all gases consist of two atoms. 4. Molecules may be molecular, atomic or ionic in structure. 5. There is no difficulty in comparing molecules by their size. 6. Molecules are too small and cannot be seen by ordinary means.7. The electron microscopc is the most powerful instrument that is used for molecular investigations.

Ex. 3. Jumlalarni qidiring va o’zbek tiliga tarjima qiling, bir-biriga o'xshamaydigan atomlardan tashkil topgan molekulalar, shuningdek, bunday molekulalarning tavsifi berilgan takliflar haqida gaplashamiz.

Ex. 4. Respond to the following statements. Use the expressions: you are

right; yes, indeed; probably; you are not quite right; I can V agree with you.

1.1 hear you are leaving for Moscow today. 2 .1 think your work was very useful. 3 .1 think it would be better to speak to him. 4. Your results don’t verify your hypothesis. 5. The Iccturc was not very easy to understand.6. Your sister has just left school, hasn’t she? 7. As far as I know, Niels Bohr was not only a great physicist but a distinguished philosopher as well. 8. If I am not mistaken, you are very good at sports.

Ex. 5. Give detailed answers to the questions.

1. What is a molecule? 2. What determines the properties of molecules? 3. What kind of molecules are there? 4. In what way can the molecules be investigated? 5. What is the Difference between the molecules of elements and compounds.

Ex. 6. Discuss the following topics:

1. Kinds of Molecules.

2. Molecular Composition and Structure.

3. Definition of a Molecule.

4.WHAT IS IT?

The smallest particlе of matter that has the same chemical properties as the whole mass.