3 Part One. The Predicate

The Composition and Structure of Water
Water was thought by the ancients to be an element. Henry Cavendish in 1781 showed that water is formed when hydrogen is burned in air, and Lavoisier first rccognizcd that water is a compound of the two elements — hydrogen and oxygen.

The formula of water is H₂O . The relative weights of hydrogen and oxygen in the substance have been very carefully determined as 2.016:16.000. This determination has been made both by weighing the amounts of hydrogen and oxygen liberated from water by electrolysis and by determining the weights of hydrogen and oxygen that combine to form water.

Liquid water has a number of unique properties which indicate that the structure must be fundamentally different from that of most other liquids. Thus, water has high melting and boiling points, an unusually high heat capacity, and shows a characteristic decrease in molar volume on melting and a subsequent contraction between 0 and 4°C. Quite apart from the behaviour of aqueous solutions, any proposed structure for liquid water must be consistent with these observations.

From spcctroscopic studies of isolated water molecules in the gas phase, it has been shown that the H—О—H bond angle is very nearly the tetrahedral angle of 105° and the О—H intcmuclcar distance is 0.97E; the observed dipole moment is 1.87x10^-18 c.s.u.* acting along the biscctor of the H—О—H angle.

Bemal and Fowler in a classical work on the interpretation of these results, showed that the net electronic density distribution was consistent with such a structure in which, in addition to the two protons carrying small positive chargcs, there are also two regions of negative charge. These four regions of charge, two positive and two negative, could be regarded as residing at the corners of a tetrahedron. If the oxygen is approximately sp³ hybridized then two o f the orbitals on the oxygen atom are used for bonding the hydrogen atoms and the other two cany the lone pairs of electrons which can participate in hydrogen bonds to two neighbouring water molecules. In terms of this picture the structure of ice, in which each molecule has four nearest neighbours, can be represented in the following way. The molecules are held together by tctrahcdrally-dirccted hydrogen bonds which are essentially electrostatic in character. The structure is an open one rather than a close-packed with a resulting increase in density. The characteristic increase in density with temperature continues until 4°C when die expeetcd decrease accompanying the increased thermal energy becomes apparent.
Words and Word-Combinations to Be Memorized

accompany, apart, apparent, aqueous, behaviour, capacity, careful, character, charge, consistent, dipole, energy, expect, liberate, moment, net, a number of, observation, partial, participate, positive, region, spcctroscopc, static, unusually

Ex. 5. Fill in the blanks with prepositions where necessary.

1. Cavendish ... 1781 showed water to be formed when oxygen is burned ... air. 2. The relative weights ... hydrogen and oxygen ... the substance were very carefully determined. 3. Water ... the liquid phase has a number... unique properties. 4. The structure ... water is different... that... most... other liquids. 5. It was shown ... spcctroscopic studies that the H—О—H bond angle is very nearly the tetrahedral angle... 105°.6. The molecules ... icc are held together ... tetrahcdrally-direetcd hydrogen bonds. 7. These bonds are essentially electrostatic ... character.

Ex. 6. Translate the sentences into Uzbek, paying attention to different functions of the word will.

1. The laboratory of analytical chemistry willsoon be transferred to a new building. 2. Heating w ill affect the state o f water but not its composition. 3. Other ways of obtaining hydrogen willbcdiscusscd in the next chaptcr. 4. Water is usually called a universal solvent because it will dissolve a tremendous number of substances. 5. Willyou give me your dictionary for a couplc of days? 6. He went to the university against his father’s will.7. There willbe no difficulty in making calculations.

Ex. 7. Translate the sentences into Uzbek.

1. That air is not a chemical compound is now known even to children, but there was a time when it was thought to be an clement. 2. The chemists have many problems to solve, particularly environmental ones. 3. One has to remember that a reaction with the liberation of heat may be followed by an explosion. 4. It is sometimes not easy to decide what catalyst should be used. 5. For a number of chemical processes it is desirable to use distilled water. 6. To obtain sufficiently pure water is one of the urgent problems of the day, especially in chemical and paper industries. 7. Boiling is one of the simplest ways of purifying water.8. Barium sulphate is only slightly soluble, one can easily separate it by means of a filter. 9. They watchcd the temperature rising, but at the temperature of 69 degrees the process stopped. 10. Phosphorus is very interesting by existing in several allotropic forms. 11. Never take white phosphorus with bare hands because heat of the body is enough to ignite it. 12. It is its activity with oxygen that is the most striking property of phosphorus. 13. Compounds of silicon are found to make up about 87 percent of the outer layer of the solid earth. 14. Atoms are generally known to be electrically neutral. 15. Hydrogen atom is stated to contain no neutrons. 16. They supposed the substance to react at room temperature, but it wouldn’t. 17. Combining the two mixtures may result in an explosion. 18. To find free chlorine in nature is impossible because of its exceedingly high activity. 19. Chlorine is considered to be a typical non-metal. 20. For hydrogen to combinc with chlorine with appreciable velocity in the dark is possible in the presence of a catalyst. 21. The experiments show chlorine to be an activc oxidizing agent. 22. That the lightest of the alkali metals is lithium can be determined by its position in the periodic table. 23. One can observe caesium taking fire at ordinary temperature. 24. Molecular structure of nitrogen allows the properties of this element to be accounted for. 25. Nitrogen can be made to form ammonia by use of a suitable catalyst. 26. Whether the hypothesis is true must be verified experimentally. 27. The aim of this experiment is to show whether sulphuric acid will react with metals. 28. Lomonosov's being the first who formulated the second law of thermodynamics is seldom mentioned. 29. It is heating that forces many reactions to take place. 30. A great number of elements have been found to have two or more isotopes.

Ex. 8. Translate the sentences into English.

1. Qadimgi davrlarda suv elementlardan biri ekanligiga ishonishgan.2. Faqat XVIII asr oxirida suv ikki elementdan - vodorod va kisloroddan iborat ekanligi isbotlandi. 3. Endi har bir o'quvchi suvning H₂O formula ekanligini biladi. 4. Suyuq holatda bo'lgan suv bir qator o'ziga xos xususiyatlarga ega. 5. Suvning g'ayrioddiy temir yo'l ekanligi uning tuzilishi bilan izohlanadi, 6. Gaz va qattiq fazalarda suvni o'rganish ham qiziq. 7. Suvning xarakterli fizik xususiyatlari yuqori eritish va qaynash nuqtalarini, shuningdek issiqlik sig'imini o'z ichiga oladi.

Ex. 11. Answer the following questions:

1. By means of what experiment was it shown that water is a compound?

2. What is the composition of water? 3. What properties show water to be a unique liquid? 4. In what way can the properties of water be accounted for? 5. What did spectroscopic studies of water molecules show? 6. In what way are the atoms in the water molecule held together?