Water was thought by the ancients to be an clement. Henry Cavendish in +1781 showed that water is formed when hydrogen is burned in air, and Lavoisier first recognized that water is a compound of the two elements - hydrogen and oxygen.
The formula of water is H20. The relative weights of hydrogen and oxygen in the substancc 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 spectroscopic studies of isolated water molcculcs in the gas phase, it has been shown that the H-О-H bond angle is very nearly the tctrahcdral angle of 105 ° and the О-H intcrnuclcar distance is 0.97E; the observed dipolc moment is 1.87x10 "18 c.s.u.  acting along the bisector of the H-О-H angle.
Bcrnal 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 charges, there arc 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 of the orbitals on the oxygen atom arc used for bonding the hydrogen atoms and the other two carry the lone pairs of electrons wrhich can participate in hydrogen bonds to two neighbouring water molcculcs. In terms of this picture the structure of icc, in which cach molcculc has four nearest neighbours, can be represented in the following way. The molecules arc held together by tctrahcdrally-dircctcd hydrogen bonds which arc 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 cxpcctcd dccrcasc 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, spectroscope, static, unusually
Ex. 5. Give the Russian equivalents for the following:
. relative weights, determine very carefully, liberate hydrogen, a number * of unique properties, heat capacity, the behaviour of aqueous solutions, be consistent with, spectroscopic studies, the bond angle, the interpretation of results, in addition to the protons, positive charge , at the comers of a tetrahedron, participate in hydrogen bonds, represent the structure, be electrostatic in character, thermal energy
Ex. 6. Give the English equivalents for the following:
склад води, на повітрі, визнавати, рідка вода, відрізнятися від, високі точки плавлення і кипіння, незвично висока теплоємність, в газовій фазі, мсж'ядсрнос відстань, класична робота, негативний заряд, воднева зв'язок, сусідні молекули води, структура льоду, таким чином, утримувати разом, бути якимось л. за характером, а не часткове руйнування структури, збільшення щільності, очікуване зменшення, стає очевидним
Ex. 7. Fill in the blanks with prepositions where necessary.
1. Cavendish ... 1 781 showed water to be formed when oxygen is burned ... air. 2. The relative weights ... hydrogen and oxygen ... the substancc 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 ... spectroscopic studies that the H-О-H bond angle is very nearly the tctrahcdral angle ... 105 °. 6. The molcculcs ... ice arc held together ... tctrahcdrally-dircctcd hydrogen bonds. 7. These bonds arc essentially electrostatic ... character.
Ex. 8. Translate the sentences into Russian, paying attention to different functions of the word will.
1. The laboratory of analytical chcmistry will soon be transferred to a new building. 2. Heating will affcct the state of water but not its composition. 3. Other ways of obtaining hydrogen n? 7 / bc discusscd in the next chaptcr. 4. Water is usually callcd a universal solvent bccausc it wilt dissolve a tremendous number of substanccs. 5. І 111 you give me your dictionary for a couple of days? 6. He went to the university against his father's will. 7. There will be no difficulty in making calculations.
Ex. 9. Translate the sentences into Russian.
1. That air is not a chcmical compound is now known even to children, but there was a time when it was thought to be an element. 2. The chcmists 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 dccidc what catalyst should be used. 5. For a number of chcmical processes it is desirable to use distilled wratcr. 6. To obtain sufficiently pure water is one of the urgent problems of the day, especially in chcmical 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 watched the temperature rising, but at the temperature of 69 degrees the proccss stopped. 10. Phosphorus is very interesting by existing in several allotropic forms. 11. Never take white phosphorus with bare hands bccausc 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 per ccnt of the outer layer of the solid earth. 14. Atoms arc generally known to be electrically neutral. 15. Hydrogen atom is stated to contain no neutrons. 16. They supposed the substancc to rcact at room temperature, but it would not. 17. Combining the two mixtures may result in an explosion. 18. To find free chlorinc in nature is impossible bccausc of its exceedingly high activity. 19. Chlorinc is considered to be a typical non-metal. 20. For hydrogen to combine with chlorinc with appreciable velocity in the dark is possible in the presence of a catalyst. 21. The experiments show chlorinc 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 tabic. 23. One can observe caesium taking fire at ordinary temperature. 24. Molecular structure of nitrogen allows the properties of this clement to be accountcd 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 sccond law of thermodynamics is seldom mentioned. 29. It is heating that forccs many reactions to take placc. 30. A great number of elements have been found to have two or more isotopes.
Ex. 10. Translate the sentences into English.
1. У давні часи вважали, що вода - це один з елементів. 2. Тільки в кінці XVIII століття було доведено, що вода складається з двох елементів - водню і кисню. 3. Тепер кожному школяреві відомо, що формула води - Н20. 4. Вода в рідкому стані має низку унікальних властивостей. 5. Те, що вода - незвичайна рідина, пояснюється се структурою, б. Цікаво також вивчення води в газоподібному і твердій фазі. 7. Характерними фізичними властивостями води можна назвати високі точки плавлення і кипіння, а також теплоємність.
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 wratcr be accounted for? 5. What did spectroscopic studies of water molcculcs show? 6. In what way arc the atoms in the water molcculc held together?
Упр. 1. Назвіть значення наступних інтернаціональних слів:
component, ion, metal, ocean, complex, oiganic, organism, course, plasma, extensively, correlate, universal, barium, sulphate, milligram, litre, quartz, extremely, ccllulosc
Упр. 2. Визначте значення виділених слів по контекст} '.
1. The ability of water to dissolve many substanccs is one of its unique properties. 2. Heat and light arc usually evolved during combustion. 3. A substancc that is dissolved is callcd a solute. 4. Water is widely used both in industry and in laboratory. 5. If a solution of NaCl is evaporated to dryness, white crystals appear in the glass. 6. If a solution is saturated, no more solute can be dissolved.
Слова до тексту:
environment - навколишнє середовище; tissue - тканина; fluid - рідина; blood - кров; cell - клітина; imperceptible - непомітний, незначний; vessel - посудину; eventually - врешті-решт; merely - просто; exceedingly - надзвичайно
Text 9 В | Fluorine | Lesson 10 | Text 10 В | Lesson 11 | Fascinating Phosphorus | Modifications of Phosphorus | Lesson 12 | Chemical Symbols for Representing Compounds | Weight of У12 atom of carbon 12 |