Английский. пособие Химики АЯ. Introduction
 Скачать 3.05 Mb.
|
|
7. Explain in English the following terms using a specialized dictionary, give their Russian equivalents and make up your own sentences with them. 1) population density; 2) water waste management; 3) coagulation; 4) flocculation; 5) irrigation,; 6)infiltration. 8. Give English translation for: Очистка сточных вод – комплекс мероприятий по удалению загрязнений, содержащихся в бытовых и промышленных сточных водах. Очищение происходит в несколько этапов: механический, биологический, физико-химический, химический. На механическом этапе происходит предварительная очистка поступающих на очистные сооружения сточных вод с целью подготовки их к биологической очистке. Биологическая очистка предполагает деградацию органической составляющей сточных вод микроорганизмами. На данном этапе происходит минерализация сточных вод, удаление органического азота и фосфора, главной целью является снижение потребления кислорода. Физико-химические методы используют для очистки сточных вод от грубо- и мелкодисперсионных частиц, коллоидных примесей, растворенных соединений. Химическая очистка применяется для выделения из сточных вод растворимых неорганических примесей. При обработке сточных вод реагентами происходит их нейтрализация, выделение растворенных соединений, обесцвечивание и обеззараживание стоков. В настоящее время из общего количества сточных вод механической очистки подвергается 68 % всех стоков, физико-химической – 3 %, биологической – 29 %. В перспективе предполагается повысить долю очистки биологическим методом до 80 %, что улучшит качество очищаемой воды. 9. Prepare a short presentation on the topic: ‘Environment Management’. Use information of specialized reference books, encyclopedias, web sites. 10. Write an article for a student magazine about water waste management. SUPPLEMENTARY READING Unit 1 Chemistry Chemistry is the science that deals with the properties, composition, and structure of substances (defined as elements and compounds), the transformations they undergo, and the energy that is released or absorbed during these processes. Every substance, whether naturally occurring or artificially produced, consists of one or more of the hundred-odd species of atoms that have been identified as elements. Although these atoms, in turn, are composed of more elementary particles, they are the basic building blocks of chemical substances; there is no quantity of oxygen, mercury, or gold, for example, smaller than an atom of that substance. Chemistry, therefore, is concerned not with the subatomic domain but with the properties of atoms and the laws governing their combinations and how the knowledge of these properties can be used to achieve specific purposes. The great challenge in chemistry is the development of a coherent explanation of the complex behaviour of materials, why they appear as they do, what gives them their enduring properties, and how interactions among different substances can bring about the formation of new substances and the destruction of old ones. From the earliest attempts to understand the material world in rational terms, chemists have struggled to develop theories of matter that satisfactorily explain both permanence and change. The ordered assembly of indestructible atoms into small and large molecules, or extended networks of intermingled atoms, is generally accepted as the basis of permanence, while the reorganization of atoms or molecules into different arrangements lies behind theories of change. Thus chemistry involves the study of the atomic composition and structural architecture of substances, as well as the varied interactions among substances that can lead to sudden, often violent reactions. Chemistry also is concerned with the utilization of natural substances and the creation of artificial ones. Cooking, fermentation, glass making, and metallurgy are all chemical processes that date from the beginnings of civilization. Today, vinyl, Teflon, liquid crystals, semiconductors, and superconductors represent the fruits of chemical technology. The 20th century has seen dramatic advances in the comprehension of the marvelous and complex chemistry of living organisms, and a molecular interpretation of health and disease holds great promise. Modern chemistry, aided by increasingly sophisticated instruments, studies materials as small as single atoms and as large and complex as DNA (deoxyribonucleic acid), which contains millions of atoms. New substances can even be designed to bear desired characteristics and then synthesized. The rate at which chemical knowledge continues to accumulate is remarkable. Over time more than 8,000,000 different chemical substances, both natural and artificial, have been characterized and produced. The number was less than 500,000 as recently as 1965. Intimately interconnected with the intellectual challenges of chemistry are those associated with industry. In the mid-19th century the German chemist Justus von Liebig commented that the wealth of a nation could be gauged by the amount of sulfuric acid it produced. This acid, essential to many manufacturing processes, remains today the leading chemical product of industrialized countries. As Liebig recognized, a country that produces large amounts of sulfuric acid is one with a strong chemical industry and a strong economy as a whole. The production, distribution, and utilization of a wide range of chemical products is common to all highly developed nations. In fact, one can say that the “iron age” of civilization is being replaced by a “polymer age,” for in some countries the total volume of polymers now produced exceeds that of iron. The Methodology of Chemistry Chemistry is to a large extent a cumulative science. Over time the number and extent of observations and phenomena studied increase. Not all hypotheses and discoveries endure unchallenged, however. Some of them are discarded as new observations or more satisfying explanations appear. Nonetheless, chemistry has a broad spectrum of explanatory models for chemical phenomena that have endured and been extended over time. These now have the status of theories, interconnected sets of explanatory devices that correlate well with observed phenomena. As new discoveries are made, they are incorporated into existing theory whenever possible. However, as the discovery of high-temperature superconductors in 1986 illustrates, accepted theory is never sufficient to predict the course of future discovery. Serendipity, or chance discovery, will continue to play as much a role in the future as will theoretical sophistication. The Scope of Chemistry The days are long past when one person could hope to have a detailed knowledge of all areas of chemistry. Those pursuing their interests into specific areas of chemistry communicate with others who share the same interests. Over time a group of chemists with specialized research interests become the founding members of an area of specialization. The areas of specialization that emerged early in the history of chemistry, such as organic, inorganic, physical, analytical, and industrial chemistry, along with biochemistry, remain of greatest general interest. There has been, however, much growth in the areas of polymer, environmental, and medicinal chemistry during the 20th century. Moreover, new specialities continue to appear, as, for example, pesticide, forensic, and computer chemistry. Physical Chemistry Many chemical disciplines, such as those already discussed, focus on certain classes of materials that share common structural and chemical features. Other specialties may be centred not on a class of substances but rather on their interactions and transformations. The oldest of these fields is physical chemistry, which seeks to measure, correlate, and explain the quantitative aspects of chemical processes. The Anglo-Irish chemist Robert Boyle, for example, discovered in the 17th century that at room temperature the volume of a fixed quantity of gas decreases proportionally as the pressure on it increases. Thus, for a gas at constant temperature, the product of its volume V and pressure P equals a constant number – i. e., PV = constant. Such a simple arithmetic relationship is valid for nearly all gases at room temperature and at pressures equal to or less than one atmosphere. Subsequent work has shown that the relationship loses its validity at higher pressures, but more complicated expressions that more accurately match experimental results can be derived. The discovery and investigation of such chemical regularities, often called laws of nature, lie within the realm of physical chemistry. For much of the 18th century the source of mathematical regularity in chemical systems was assumed to be the continuum of forces and fields that surround the atoms making up chemical elements and compounds. Developments in the 20th century, however, have shown that chemical behaviour is best interpreted by a quantum mechanical model of atomic and molecular structure. The branch of physical chemistry that is largely devoted to this subject is theoretical chemistry. Theoretical chemists make extensive use of computers to help them solve complicated mathematical equations. Other branches of physical chemistry include chemical thermodynamics, which deals with the relationship between heat and other forms of chemical energy, and chemical kinetics, which seeks to measure and understand the rates of chemical reactions. Electrochemistry investigates the interrelationship of electric current and chemical change. The passage of an electric current through a chemical solution causes changes in the constituent substances that are often reversible – i. e., under different conditions the altered substances themselves will yield an electric current. Common batteries contain chemical substances that, when placed in contact with each other by closing an electrical circuit, will deliver current at a constant voltage until the substances are consumed. At present there is much interest in devices that can use the energy in sunlight to drive chemical reactions whose products are capable of storing the energy. The discovery of such devices would make possible the widespread utilization of solar energy. There are many other disciplines within physical chemistry that are concerned more with the general properties of substances and the interactions among substances than with the substances themselves. Photochemistry is a specialty that investigates the interaction of light with matter. Chemical reactions initiated by the absorption of light can be very different from those that occur by other means. Vitamin D, for example, is formed in the human body when the steroid ergosterol absorbs solar radiation; ergosterol does not change to vitamin D in the dark. A rapidly developing subdiscipline of physical chemistry is surface chemistry. It examines the properties of chemical surfaces, relying heavily on instruments that can provide a chemical profile of such surfaces. Whenever a solid is exposed to a liquid or a gas, a reaction occurs initially on the surface of the solid, and its properties can change dramatically as a result. Aluminum is a case in point: it is resistant to corrosion precisely because the surface of the pure metal reacts with oxygen to form a layer of aluminum oxide, which serves to protect the interior of the metal from further oxidation. Numerous reaction catalysts perform their function by providing a reactive surface on which substances can react. Unit 2 Studies of Molecular Structure The chemical properties of a substance are a function of its structure, and the techniques of X-ray crystallography now enable chemists to determine the precise atomic arrangement of complex molecules. A molecule is an ordered assembly of atoms. Each atom in a molecule is connected to one or more neighbouring atoms by a chemical bond. The length of bonds and the angles between adjacent bonds are all important in describing molecular structure, and a comprehensive theory of chemical bonding is one of the major achievements of modern chemistry. Fundamental to bonding theory is the atomic–molecular concept. Atoms and Elements As far as general chemistry is concerned, atoms are composed of the three fundamental particles: the proton, the neutron, and the electron. Although the proton and the neutron are themselves composed of smaller units, their substructure has little impact on chemical transformation. As was explained in an earlier section, the proton carries a charge of +1, and the number of protons in an atomic nucleus distinguishes one type of chemical atom from another. The simplest atom of all, hydrogen, has a nucleus composed of a single proton. The neutron has very nearly the same mass as the proton, but it has no charge. Neutrons are contained with protons in the nucleus of all atoms other than hydrogen. The atom with one proton and one neutron in its nucleus is called deuterium. Because it has only one proton, deuterium exhibits the same chemical properties as hydrogen but has a different mass. Hydrogen and deuterium are examples of related atoms called isotopes. The third atomic particle, the electron, has a charge of – 1, but its mass is 1,836 times smaller than that of a proton. The electron occupies a region of space outside the nucleus termed an orbital. Some orbitals are spherical with the nucleus at the centre. Because electrons have so little mass and move about at speeds close to half that of light, they exhibit the same wave–particle duality as photons of light. This means that some of the properties of an electron are best described by considering the electron to be a particle, while other properties are consistent with the behaviour of a standing wave. The energy of a standing wave, such as a vibrating string, is distributed over the region of space defined by the two fixed ends and the up-and-down extremes of vibration. Such a wave does not exist in a fixed region of space as does a particle. Early models of atomic structure envisioned the electron as a particle orbiting the nucleus, but electron orbitals are now interpreted as the regions of space occupied by standing waves called wave functions. These wave functions represent the regions of space around the nucleus in which the probability of finding an electron is high. They play an important role in bonding theory, as will be discussed later. Each proton in an atomic nucleus requires an electron for electrical neutrality. Thus, as the number of protons in a nucleus increases, so too does the number of electrons. The electrons, alone or in pairs, occupy orbitals increasingly distant from the nucleus. Electrons farther from the nucleus are attracted less strongly by the protons in the nucleus, and they can be removed more easily from the atom. The energy required to move an electron from one orbital to another, or from one orbital to free space, gives a measure of the energy level of the orbitals. These energies have been found to have distinct, fixed values; they are said to be quantized. The energy differences between orbitals give rise to the characteristic patterns of light absorption or emission that are unique to each chemical atom. A new chemical atom – that is, an element – results each time another proton is added to an atomic nucleus. Consecutive addition of protons generates the whole range of elements known to exist in the universe. Compounds are formed when two or more different elements combine through atomic bonding. Such bond formation is a consequence of electron pairing and constitutes the foundation of all structural chemistry. Ionic and Covalent Bonding When two different atoms approach each other, the electrons in their outer orbitals can respond in two distinct ways. An electron in the outermost atomic orbital of atom A may move completely to an outer but stabler orbital of atom B. The charged atoms that result, A+ and B-, are called ions, and the electrostatic force of attraction between them gives rise to what is termed an ionic bond. Most elements can form ionic bonds, and the substances that result commonly exist as three-dimensional arrays of positive and negative ions. Ionic compounds are frequently crystalline solids that have high melting points (e. g., table salt). The second way in which the two outer electrons of atoms A and B can respond to the approach of A and B is to pair up to form a covalent bond. In the simple view known as the valence-bond model, in which electrons are treated strictly as particles, the two paired electrons are assumed to lie between the two nuclei and are shared equally by atoms A and B, resulting in a covalent bond. Atoms joined together by one or more covalent bonds constitute molecules. Hydrogen gas is composed of hydrogen molecules, which consist in turn of two hydrogen atoms linked by a covalent bond. The notation H2 for hydrogen gas is referred to as a molecular formula. Molecular formulas indicate the number and type of atoms that make up a molecule. The molecule H2 is responsible for the properties generally associated with hydrogen gas. Most substances on Earth have covalently bonded molecules as their fundamental chemical unit, and their molecular properties are completely different from those of the constituent elements. The physical and chemical properties of carbon dioxide, for example, are quite distinct from those of pure carbon and pure oxygen. The interpretation of a covalent bond as a localized electron pair is an oversimplification of the bonding situation. A more comprehensive description of bonding that considers the wave properties of electrons is the molecular-orbital theory. According to this theory, electrons in a molecule, rather than being localized between atoms, are distributed over all the atoms in the molecule in a spatial distribution described by a molecular orbital. Such orbitals result when the atomic orbitals of bonded atoms combine with each other. The total number of molecular orbitals present in a molecule is equal to the sum of all atomic orbitals in the constituent atoms prior to bonding. Thus, for the simple combination of atoms A and B to form the molecule AB, two atomic orbitals combine to generate two molecular orbitals. One of these, the so-called bonding molecular orbital, represents a region of space enveloping both the A and B atoms, while the other, the anti-bonding molecular orbital, has two lobes, neither of which occupies the space between the two atoms. The bonding molecular orbital is at a lower energy level than are the two atomic orbitals, while the anti-bonding orbital is at a higher energy level. The two paired electrons that constitute the covalent bond between A and B occupy the bonding molecular orbital. For this reason, there is a high probability of finding the electrons between A and B, but they can be found elsewhere in the orbital as well. Because only two electrons are involved in bond formation and both can be accommodated in the lower energy orbital, the anti-bonding orbital remains unpopulated. This theory of bonding predicts that bonding between A and B will occur because the energy of the paired electrons after bonding is less than that of the two electrons in their atomic orbitals prior to bonding. The formation of a covalent bond is thus energetically favoured. The system goes from a state of higher energy to one of lower energy. Another feature of this bonding picture is that it is able to predict the energy required to move an electron from the bonding molecular orbital to the anti-bonding one. The energy required for such an electronic excitation can be provided by visible light, for example, and the wavelength of the light absorbed determines the colour displayed by the absorbing molecule (e. g., violets are blue because the pigments in the flower absorb the red rays of natural light and reflect more of the blue). As the number of atoms in a molecule increases, so too does the number of molecular orbitals. Calculation of molecular orbitals for large molecules is mathematically difficult, but computers have made it possible to determine the wave equations for several large molecules. Molecular properties predicted by such calculations correlate well with experimental results. |