The more profound is the investigation of the structure of atoms and molcculcs, the more problems arise. It was not long ago that consideration
of the cxtra-nuclcar clcctrons was rcstrictcd to an indication (hat their number must equal the atomic number of the clement, 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 discusscd 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 spcctrum, but gases and vapours under the same conditions, when examined spcctroscopically, show a series often very complicated, of distinct lines or bands occupying definite positions, diat is, with definite wave lengths. The more information conccrning the composition of various spectra was obtained, the clearer it became that the line spectra arc produced by atoms and so arc 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 spaccd lines, arc obtained from molcculcs.
A line spectrum is the one formed when radiation from an incandescent gas is passed through a slit and then dispersed. The lines arc produced by energy changcs when electrons pass from high energy quantum levels to low energy quantum levels. The clcctrons arc 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 spcctrum, a scries of fairly broad bands is formed. These bands arc sharp at one edge but dying away on the other. They arise from the complex energy changcs possible in a molcculc. Under high resolution, the band is shown to be made up of many lines sharper and clcarcr 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 complcx the molcculc, the more complicated the spcctrum is.
It is from atomic spcctra in particular diat information conccrning the cxtra-nuclcar electrons has been obtained.
Words and Word-Combinations to Be Memorized
band, complicated, concerning, on/under condition, connection, in conncction with, diffusion, disperse, edge, emit, examination, excite, extra, in fact, the fact that, head, incandescent, infrared, investigate, length, most likely, not likely, nuclear, optical, in panicular, pass, radiation, radiate, slit, spectroscopy, the... the..., unlikely, voltage
Ex. 5. Give the Russian equivalents for the following:
a profound investigation, restrict consideration to, mention the fact, in this conncction, examine a spcctrum, heat to incandescence, examine spcctroscopically, a distinct line, resolve into a number of lines, pass from one level to another, excite electrons, by the input of energy, in a discharge
8 Степаном
lube, a series of bands, arise from energy changcs, under high resolution, information concerning extra-nuclear electrons
Ex. 6. Give the English equivalents for the following:
равняться атомному номеру элемента, относительно открытая структура, расположение электронов, оптический спсктр, в инфракрасной области, испускать непрерывный спсктр, при тех же условиях, занимать определенные положения, длина волны, получать информацию, линейный спсктр, близко расположенные друг к другу линии, раскаленный газ, пропускать через щель, высокое напряжение, на одном конце, в частности
Ex. 7. Fill in the blanks with articles where ncccssary.
1__ more is known about... spectra,... more questions arise. 2. When
... solid is heated to ... incandescence, it emits ... spectrum. 3. ... line spectra arc produced by... atoms. 4.... electrons are cxcited 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, clear, actually, get, give, likely, complcx
Ex. 9. Give antonyms for the following:
disappear, rcccntly, closcd, different, indefinite, small, low, simple
Ex. 10. Translate the sentences into Russian.
1. It is not unusual to consider elements from the point of view of their properties. 2. Not unfrequcntly 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 arc for arranging them. 5. The smaller the chargcs earned 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 closcr agreement, the more strictly the instruction is followed. 9. The accuracy of weighing is not inconsiderably influenced by the sensitivity of the balancc 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. 1S. The earlier the history of chcmistry, the more striking it is. 16. Not unfrequcntly 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 arc not uncommonly revised after thorough studies in laboratories.
Ex. 11. Translate the sentences into English without using a dictionary.
1. Существует множество методов изучения структуры атомов и молекул. 2. Ценную информацию в этой связи можно получить из исследования спектров. 3. Ученые различают спсктры атомов и молекул. 4. Атомы дают линейные спсктры. S. Молекулярные спектры называют полосатыми.
Ex. 12. Answer the following questions:
1. What information can one obtain from an examination of spectra? 2. What kinds of spectra arc known? 3. When does a solid emit a spectrum? 4. Under what condition docs a gas emit a spectrum? 5. What spectrum is callcd linear? 6. What is the difference between linear and band spectra?
Section II
Упр. 1. Назовите значения следующих интернациональных слов:
associate, surprise, doctor, demonstrate, composition, spcctroscopc, astronomy, detect, spcctrographcr, priority, journal, practically, publicity, publish, prestigious, reputation, orange, prevalent, characteristic, construct
Упр. 2. Проверьте, помните ли вы значения следующих слов; если нет, обратитесь к словарю:
scrutiny, be accustomed to, point out, celestial, application, in behalf of, flame, inaccessiblc, seek to, confuse, obstruct, stumble, discourage