3 Part One. The Predicate

Investigations of Spectra
The more profound is the investigation o f the structure of atoms and molecules, the more problems arise. It was not long ago that considerationof the extra-nuclear electrons was restricted to an indication that their number must equal the atomic number of the element, and to a mention of the fact that they form a relatively open structure about the ccntral nucleus.

The question of their arrangement must now be discussed in detail, and in this conncction valuable information has been obtained from an examination of both optical and X-ray spectra, the former term being used to describe spectra in the ultraviolet, visible and infra-red regions.

When a solid is heated to incandcsccncc, it emits a more or less continuous spectrum, but gases and vapours under the same conditions, when examined spectroscopically, show a scries often very complicated, of distinct lines or bands occupying definite positions, that is, with definite wave lengths. The more information concerning the composition of various spectra was obtained, the clcarer it bccamc that the line spectra are produced by atoms and so are not unfrcqucntly referred to as atomic spectra, whereas the so-called band spectra, which can, in fact, often be resolved into large number of closely spaced lines, are obtained from molecules.

A line spectrum is the one formed when radiation from an incandcsccnt gas is passed through a slit and then dispersed. The lines are produced by energy changes when electrons pass from high energy quantum levels to low energy quantum levels. The electrons are cxcitcd from low to high levels by the input of energy into the gas — usually in a discharge tube under a high voltage.

In a molecular spectrum, a scries of fairly broad bands is formed. These bands are sharp at one edge but dying away on the other. They arise from the complex energy changes possible in a molecule. Under high resolution, the band is shown to be made up of many lines sharper and clcarer together at the head of the band but more diffuse away from the head of the band. It seems not at all unlikely that the more complex the molecule, the more complicated the spectrum is.

It is from atomic spectra in particular that information concerning the extra-nuclcar electrons has been obtained.

Words and Word-Combinations to Be Memorized

band, complicated, concerning, on/under condition, conncction, in conncction with, diffusion, disperse, edge, emit, examination, cxcite, extra, in fact, the fact that, head, incandcsccnt, infrared, investigate, length, most likely, not likely, nuclear, optical, in particular, pass, radiation, radiate, slit, spectroscopy, the... the..., unlikely, voltage

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

a profound investigation, restrict consideration to, mention the fact, in this conncction, examine a spectrum, heat to incandesccncc, examine spectroscopically, a distinct line, resolve into a number of lines, pass from one level to another, cxcitc electrons, by the input of energy, in a discharge tube, a scries of bands, arise from energy changes, under high resolution, information concerning extra-nuclear electrons

Ex. 6. Give the English equivalents for the following:

elementning atom raqamiga teng, nisbatan ochiq struktura, elektronlarning joylashishi, optik spektr, infraqizil ichida doimiy spektr chiqaradi, xuddi shu sharoitda, ma'lum bir pozitsiyalarni egallaydi, to'lqin uzunligi, ma'lumot oladi, chiziqli spektr, bir-biriga yaqin chiziqlar, issiq gaz ushlagich orqali o'ting, ayniqsa, uchida yuqori kuchlanish

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

1 more is known about... spectra,... more questions arise. 2. When... solid is heated to ... incandcsccncc, it emits ... spectrum. 3. ... line spectra are produced b y ... atoms. 4 .... electrons are excited in ... discharge tube under... high voltage. S information concerning... extra-nuclear electrons has been obtained particularly from ... atomic spectra.

Ex. 8. Give synonyms for the following:

examination, be limited to, question, important, evolve, a number of, dear, actually, get, give, likely, complex

Ex. 9. Give antonyms for the following:

disappear, recently, closed, different, indefinite, small, low, simple

Ex. 10. Translate the sentences into Uzbek.

1. It is not unusual to consider elements from the point of view of their properties. 2. Not unfrcqucntly water itself acts as a catalyst in many reactions. 3. The higher the temperature, the greater is the viscosity of gases. 4. The greater the number of carbon atoms in a given structure, the more ways there are for arranging them. 5. The smaller the chargcs carried by the ions of a crystal and the larger the ionic radii, the weaker the forces that bind the ions to one another within the crystal, and the more readily the crystal structure is broken down. 6. It is not improbable that the results of their work will be similar to ours. 7. Vaporization proceeds faster, the higher is the temperature, pressure being constant. 8.The results will be in closer agreement, the more strictly the instruction is followed. 9. The accuracy of weighing is not inconsiderably influenced by the sensitivity of the balance used. 10. Under these conditions concentration is higher, the higher the temperature. 11. The harder you study, the better you master the subject. 12. The reaction is more efficient, the purer the chemicals. 13. The smaller the number of the element, the lighter it is. 14. The greater the quantity of heat possessed by the body, the greater is its hotness. 1 5. The earlier the history of chemistry, the more striking it is. 16. Not unfrcqucntly the word has several meanings, c. g., the word “theory". 17. It seemed not improbable that some elements occur as a mixture of isotopes in nature.18. It is not at all unlikely that new elements will be discovered. 19. The properties of the element are not inconsiderably influenced by their atomic number. 20. The atomic weights of elements are not uncommonly revised after thorough studies in laboratories.

Ex. 11. Translate the sentences into English without using a dictionary.

1. Atomlar va molekulalarning tuzilishini o'rganish uchun ko'plab usullar mavjud. 2. Bu borada qimmatli ma'lumotlarni spektrlarini o'rganishdan olish mumkin. 3. Olimlar atomlar va molekulalar spektrlarini farqladidilar. 4. Atomlar chiziqli spektrlarni beradi.

Ex. 12. Answer the following questions:

1. What information can one obtain from an examination of spectra?

2. What kinds of spectra are known? 3. When does a solid emit a spectrum? 4. Under what condition does a gas emit a spectrum? 5. What spectrum is called linear? 6. What is the difference between linear and band spectra?