To the modern chcmist, the atom is the smallest particle of an clement that can enter into a chcmical reaction. Thus, each clement has atoms that are peculiar to itself and different from those of each of the other elements. Chcmical reactions occur when atoms of different kinds unite to form groups in which they bear definite relationships to cach other or when these groups undergo disruption or rearrangement. Chcmical unions arc of two general types.
In one type of union, atoms bccomc bonded together to form definite aggregates that exist as independent, electrically neutral particles and arc known as molcculcs (Latin 'little mass**). Some elements have atoms that unite with others of their own kind to form molcculcs. These arc known as elemental molcculcs and arc exemplified by the chlorinc molecule which is made up of two chlorinc atoms. Compound molcculcs arc composed of two or more kinds of atoms and arc exemplified by the water molcculc, which contains two atoms of hydrogen and one of oxygen.
To give a short definition of a molcculc is not to give a more or less full account of properties.
Molcculcs arc regarded as the smallest particlcs or elementary substanccs that can have independent existence. They account for the chcmical properties and at least some of the physical properties of the substancc they constitute. A single molcculc docs not exhibit in full the physical properties commonly associated with its particular variety of matter. These properties arise both within the molcculc itself and within the aggregates of like molcculcs that constitute a sample of the given substance. The density of water depends not only on the mass and volume of indivilual molcculcs but also on the manner in which the molcculcs arc packed together. Since the chcmist works with the aggregates, their properties arc of great practical importance.
A molcculc of a compound contains, of ncccssity, at least two different atoms. An clement molcculc may contain only one atom, or it may contain two or more. Helium has monoatomic molcculcs; chlorinc and hydrogen cach exist as diatomic molecules; and sulphur molcculcs contain eight atoms. During reactions the atoms of elemental molecules usually arc separated and individually redistributed in new combinations.
Words and Word-Combinations to Be Memorized
arise, be made up of, be of importance, both... and, commonly, constitute, definition, density, depend (on), distribute, cach other, helium, independent, at least, manner, more, neutral, pack, particular, rearrangement, relationship, sample, those, type, union, within
Ex. 5. Give the Russian equivalents for the following:
enter into a chemical reaction, be different from cach other, occur, definite relationships, undergo rearrangement, chemical unions, bccomc bonded together, form definite aggregates, be exemplified by, give a full account of, account for chemical properties, a single molcculc, exhibit a property, arise within the molecule itself, density, depend on the mass, pack the molecules together, be of great practical importance, contain two or more atoms, exist as diatomic molcculcs
Ex. 6. Give the English equivalents for the following:
каждый элемент, вступать в химическую реакцию, отличаться от, электрически нейтральный, молекула хлора, состоять из, сложная молекула, молекула соединения, состоять из нескольких видов атомов, молекула воды, краткое определение, более или менее полный, по крайней мере, некоторые из свойств, отдельная молекула, в самой молекуле, образец данного вещества, плотность (удельный вес) вещества, зависеть от, иметь практическое значение, одноатомная молекула
Ex. 7. Fill in the blanks with prepositions where necessary.
1. The smallest particle of an clement that can enter ... a chcmical reaction is an atom. 2. The lecture has already begun, don't enter ... the classroom, please. 3. Elements differ... cach other. 4. Atoms ... different kinds can unite and form a molecule ... a compound. 5. Elemental molecules arc composed ... the atoms ... the same kind. 6. Chlorine molcculc is made ... two chlorine atoms. 7. This definition does not give a full account... the properties of a molcculc. 8. The density... a substance can be easily calculatcd, it depends ... its mass and volume.
Ex. 8. Translate the sentences into Russian, paying attention to different functions of since.
1. Wc call the atomic hypothesis a theory, since it has been verified by further discoveries. 2. Bohr's atomic theory has been known since 1913. 3. Chemistry has changed greatly since 1869 when the periodic law was published. 4. The periodic system has long since served as the greatest contribution to scicncc. 5. Since the combustion of many non- metals yielded products which reacted with water and gave acidic solutions, Lavoisier named the newly-discovered gas oxygen ("acid former"). 6. Ever since Lavoisier in 1792 demonstrated that diamond and graphite are allotropic forms of carbon, man has been interested in converting carbon into diamond. 7. They left St. Petersburg in 1996, they haven't been there since then.
Ex. 9. Translate the sentences into Russian.
1. To analyse a substancc means to define its components. 2. To have a laboratory practice work is very useful for students of chemistry.
3. To know the atomic structure is to understand this phenomenon.
4. To give a short definition of a molecule is not so very easy. 5. For uranium minerals to be used in industry is not a usual thing. 6. For atoms to have the same chcmical properties is to be the atoms of one clement. 7. To make accuratc measurements requires great care. 8. To start a reaction is one thing, but to keep it going on is another. 9. For molecules to have the same composition implies the existence of the same structure. 10. To think about ordinary conditions of a reaction means to think about room temperature and 1-atm pressure. 11. To speak about the properties of halogens is first of all to mention their extraordinary activity. 12. For compounds to be bonded by a covalent bond implies having one or more shared electron pairs. 13. To compare the size of molecules is rather difficult. 14. To imagine a molecule of water means to imagine a certain combination of hydrogen and oxygen atoms. 15. To obtain a spectrum is to pass a beam of white light through a spectrograph. 16. To say that the density of a substance depends only on its mass and volume is to lose sight of the manner in which the molecules are packed together.
Ex. 10. Translate the sentences into English.
1. Атомы каждого элемента отличаются от атомов других элементов. 2. Химическая реакция происходит, когда атомы взаимодействуют друг с другом и образуют новые комбинации. 3. Молекулы, как известно, электрически нейтральны. 4. Молекулы соединений состоят из двух или более видов атомов. 5. Дать определение молекулы — значит сказать о ее составе и свойствах. 6. То, что соединения имеют одинаковые физические свойства, не означает, что их химические свойства тоже одинаковы. 7. Молекула элемента может состоять из одного, двух и более одинаковых атомов.
Ex. 11. Answer the following questions:
1. What is a chemical reaction? 2. What types of chemical unions do you know? 3. What is an elemental molecule? 4. What is a compound molecule? 5. What determines the properties of a molcculc? 6. What composition an elemental molecule may have? 7. What is the difference between an atom and an elemental molecule?
Section II
Упр. 1. Назовите значения следующих интернациональных слов:
composition, identical, ozone, sort, dimethyl, amine, gas, electricity, covalent, ocean, ordinary, illuminate, optical, microscope, vision, especially
Упр. 2. Определите значения выделенных слов по контексту.
1. The boiling point of water is 100°C. 2. The original temperature of the solid was 23°C, then it was heated to 100°C. 3. When a thing is not visible by man's eye optical instruments should be used. 4. It is not possible to see atoms with the most powerful microscope. S. Some substances fail to react at room temperature. 6. It is claimed that an electron microscope is a very useful instrument for molecular investigations.
Слова к тексту:
size — размер; per — на, в; melt — плавиться; tiny — крошечный; meaningful — имеющий смысл; dye — окрашивать; throw — бросать; at random — наугад; exceedingly — чрезвычайно; directly — прямо, непосредственно; reveal — обнаружить; resolve — физ. разрешать