3 Part One. The Predicate

The Nature of a Liquid
When iodine crystals are heated to U4°C, they melt forming liquid iodine. The temperature at which the crystals and the liquid are in equilibrium — that is, at which crystals have no tendency to melt or the liquid has no tcndcncy to freeze— is called the melting pointof the crystals, and the freezing point of the liquid. This temperature is 114°C for iodine.

Liquid iodine differs from solid iodine (crystals) mainly in its fluidity. Like the solid, and unlike the gas, it has a definite volume (1 g occupics about 0.2 cm’), but it does not have a definite shape: instead, it fits itself to the shape of the bottom part of its container.

From the molecular viewpoint the process of melting can be described in the following way. As a crystal is heated, its molecules are increasingly agitated, and move about more and more vigorously, but at lower temperature, this thermal agitation does not carry any one molecule any significant distance away from the position fixed for it by the arrangement of its neighbours in the crystal. At the melting point the agitation finally becomes so great that it causes the molecules to slip by one another and to change somewhat their location relative to one anothcr. Thcy continue to stay close together, but do not continue to retain a regular fixed arrangement.

Instead, the grouping of molecules around a given molecule changcs continually, sometimes being much like the close packing of the crystal, in which cach iodine molecule has twelve near neighbours, and sometimes considerably different, the molecule has only ten or nine or eight near neighbours. Thus, a liquid, like a crystal, is a condensed phase, as contrasted with a gas, the molecules being piled rather closcly together; but whereas a crystal is characterized by regularity of atomic or molecular arrangement, a liquid is characterized by randomness of structure. The randomness of structure is usually the reason why the density o f a liquid is somewhat less than that of the corresponding crystal.

Words and Word-Combinations to Be Memorized

away, bottom, characterize, considerably, container, contrast, differ from, differ in, distance, finally, fit, fix, freeze, increasingly, instead, mainly, melt, melting point, phase point, melting, random, regular, relative, shape, significant, sometimes, somewhat, stay, that is, thermal, viewpoint

Ex. 5. Give the Uzbek equivalents for the following:

be in equilibrium, the tcndcncy for crystals to melt, freeze the liquid, differ in properties, unlike the liquid, have a definite volume, instead, fit itself to the shape of, in the following way, carry away, changc somewhat, stay elose together, the elose packing of the crystal, considerably different, a random structure, the density of a liquid

Ex. 7. Fill in the blanks with prepositons where necessary.

1. Crystals ... iodine melt when they are heated ... I14°C. 2. Liquid iodine differs ... solid iodine... its fluidity. 3. Usually, liquid fits itself... the shape... the bottom spacc ... its container. 4. The process... melting can be described... the following way. S. This process is intcrcsing... the molecular viewpoint. 6. Regularity... atomic or molecular arrangement is characteristic ... a crystal. 7. A liquid is characterized ... randomness ... structure. 8. A solid occupics ... a definite volume.

Ex. 8. Translate the sentences into Uzbek, paying attention to different functions of the words ending in - i n g .

1. Crystals melt, form ing liquid iodine. 2. The temperature at which the crystals and the liquid are in equilibrium is called the meltingpoint.3. Freezingof a liquid is very interestingto observe. 4. Healingmust be done in the following way. 5. The groupingof molecules around a given molecule changes by raisingthe temperature. 6. What are you goingto do now? 7. Attempts are beingmade to synthesize new elements in laboratory.

Ex. 9. Translate the sentences into Uzbek.

1. Who is the discoverer of the periodic law is well known not only to specialists but practically to everybody. 2. That solid, liquid and gas are the three main states of a substance is a matter of common knowledge.3. Whether these substances will react depends on the conditions o f the reaction. 4. Whether a solution is acidic or not may be easily shown using litmus paper. 5. That a particular substance contains one element or another may be determined by qualitative analysis. 6. That the vapour pressure of a crystal depends on its size is well illustrated by many experiments.7. Whether water is a compound or not may be shown by the reaction between water and some metals. 8. What ancient scientists thought was based on what they could observe around them. 9. That the alchemical period was very important in the history of chemistry is unquestionable.10. That chain molecules can be many thousands of atoms in length affects the behaviour of these substances. 11. What number of protons is there in the nucleus of the clement is known from its atomic number. 12. That water will dissolve a great number of different substances is an interesting fact. 13. That at the early stages of its development chemistry was mostly descriptive in character was quite natural. 14. Who the discoverer of nitrogen was is well known, it was isolated by Rutherford. 1 5. That students of chemistry should be able to write chemical equations readily and accurately is highly important. 16. That it was A. M. Butlerov who introduced the term “chemical structure” should not be forgotten. 17. That melting is a physical process must be quite clear to the student of chemistry.18. Whether the hydrogen bond will be broken depends on the amount of energy. 19. Who will examine us in general chemistry is not known yet. 20. That the aim of science is to explain things is a popular belief. 21. When the process started was not registered by the instrument. 22. What pressure should be applied should be decided before the experiment.

Ex. 10. Translate the sentences into English.

1. Bir fizik holatdan boshqasiga o'tish qanday amalga oshirilishini har bir talaba yaxshi tushunishi kerak. 2. Har bir modda bir xil bosimda o'zining erish nuqtasiga ega. 3. Qattiq holatning eritish nuqtasi bir vaqtning o'zida suyuqlikning muzlash nuqtasidir. 4. Ma'lumki, suyuqlik idish shaklida bo'ladi, ammo uning hajmi idish hajmiga bog'liq emas. 5. Gazdan farqli o'laroq, kristallar va suyuqlik molekulalari bir-biriga juda yaqin joylashgan. 6. Tarkibi modda holatining muhim belgilaridan biri ekanligi har doim esda qolishi kerak. 7. Kristallar tartibga solingan tuzilishga ega va suyuqlik tuzilishi o'zboshimchalik bilan bo'ladi, shuning uchun suyuqlik zichligi tegishli kristallnikidan biroz pastroqdir.

Ex. 11. Answer the following questions:

1. What temperature is called the melting point? 2. What is the difference between liquid and crystalline iodine? 3. In what way is it possible to explain the change from the solid to the liquid? 4. What is the principal difference between solid and liquid from the structural viewpoint? 5. What does the molecular motion depend on?