Unit1GeneralChemistryUnit 1 General ChemistryLesson 1 Size of Atoms and IonsThe size of atoms decreases from left to right across a period in the periodic table. For example, on moving from lithium to beryllium [ ], the number of charges on the nucleus is increased by one, so that all the orbital electrons are pulled in closer to the nucleus. In a given period, the alkali metal is the largest atom and the halogen the smallest. When a row of ten transition elements or fourteen inner transition elements occurs in a horizontal period, the contraction in size is even more marked.On descending a group in the periodic table such as lithium, sodium , potassium, rubidium, cesium, the size of the atoms increases due to the effect of extra shells of electrons being added; this outweights the effect of increased nuclear charge.A postitive ion is formed by removing one or more electrons from an atom. Normally the whole of the outer shell of electrons is removed in this way, and since the remaining inner shells do not extend so far in space, the cation is much smaller than the metal atom. In addition, the ratio of positive charges on the nucleus to the number of orbital electrons is increased. Thus the effective nuclear charge is increased and the electrons are pulled in. A positive ion is therefore smaller than the corresponding atom and the more electrons removed ( that is, the greater the charge on the ion), the smaller it becomes.Atomic radius Na 0.157 nm Atomic radius Fe 0.117nmIonic radius Na+ 0.0098nm Ionic radius Fe2+ 0.076 nmIonic radius Fe3+ 0.064 nmWhen a negative ion is formed, one or more electrons areadded to an atom, the effective nuclear charge is reduced and hence the electron cloud expends. Negative ions are bigger than the corresponding atom.Van der Waals non-bounded radius Cl 0.140nmIonic radius Cl- 0.181nmDecrease and increaseDecrease and increase vi. vt. nvi. Traffic decreases on holidays.vt. Lack of success decreases confidence.n decrease of temperatureDecrease diminish reduce shortenIncrease add to enlarge expand extend raisedescendTo move from a higher to a lower place; come or go down.To slope, extend, or incline downward:向下倾斜，向下延伸：A rough path descended like a steep stair into the plainDecline drop fall ascend rise-iumLithium, beryllium, sodim, ammonium 铵有-ium表示有金属性，没有-ium不一定不是金属：Copper, zinc, iron, mercury, gold, silverRatio of … to …The ratio of 4 to 7 is written 4: 7 or 4/7.Four seventh1/4 one fourth The ratio of 1 to 43/5 three fifthsLesson 2 Metallic CharacterMetals are electropositive and have a tendency to loss electrons, if supplied with energy. M---M++e. The stronger thistendercy, the more electropositive and more metallic an element is. The tendency to loss electrons depends on the ionization energy. Since it is easier to remove an electron from a large atom than from a small one, metallic character increases as we descend the groups in the periodic table. Thus in Group IV, carbon is a nonmetal, germanium[ ] shows some metallic properties, and tin and lead are metals. Similarly metallic character decreases from left to right across the periodic table because atomic size decreases and ionization energy increases. Thus sodium and magnesium are more metallic than silicon, which in turn, is more metallic than chlorine. The most electropositiveelements are found in the lower left of the periodic table and the most nonmetallic in the top right.Eletropositivity is really the converse of electronegativity, but it is convenient to retain the concept of electropositivity when describing metals. Strongly electropositivity elements give ionic compounds. Metallic oxides and hydroxides are basic since they ionize, and give hydroxyl ions: NaOH------Na++OH- CaO+H2O----Ca2++2 OH-Oxides, which are insoluble in water, are regarded as basic if they react with acids to form salts. Thus in the main groups of the periodic table, basic properties increase on descending a group because the elements become more electropositive and more ionic. However, this generalization does not hold for d block, and particularly for the central groups of transition elements (Cr, Mn, Fe, Co, Ni) where basicity and the ability to form simple ions decreases on descending the group.The degree of electropositivity is shown in variety of ways. Strongly electropositive elements react with water and acids. They form strongly basic oxides and hydroxides, and they reactwith oxyacids to give stable salts such as carbonates, nitrates and sulphates. Weakly electropositive elements are unaffected by water and are much less readily attacked by acids. Their oxides are frequently amphoteric, and react with both acids and alkalis. They are not basic enough to form stable carbonates.The electropositive nature of a metal is also shown in the degree of hydration of the ions. In the change: M+ to [M+ (H2O)] the positive charge becomes spread over the whole complex ion. Since the charge is no longer localized on the metal, this is almost the same as the change M+ ---M. Strongly electropositive metals have a great tendency to the opposite change: M --- M+(M+---M), so that they are not readily hydrated. The less electropositive the metal, the weaker the tendency M+ ---M and the stronger the degree of hydration. Thus the degree of hydration decrease down a group, e.g. MgCl2 6H2O and BaCl2 2 H2O.Salts of strongly electropositive metals have little tendency to hydrolyze and form oxysalts. Since the size of the metal ion is large it has little tendency to form complexes. On the other hand, salts of weakly electropositive elements hydrolyze and may form oxysalts. Because they are smaller, the metal ions have a greater tendency to form complexes.Hydro-Hydrogen hydroxide hydration hydrate hydroxyl hydrolyze Review-ide: Oxide hydroxide-ate: carbonate nitrate sulphateHydrogen hydroxide hydration hydrate hydroxyl hydrolyze Na2CO3=====Na2O+CO2C6H12O6====2C2H5OH+2CO2Lesson 3 Oxidation-Reduction ReactionSee Lesson 3.pptOxidation is the removal of electrons from, and reduction is the addition of electrons to an atom.Consider the galvanizing of iron, that is coating from with zinc to prevent rusting. The two competing reactions are : Since the zinc reaction in the forward reaction produces a larger negative potential, that is liberates more energy, the spontaneous reaction isThe coating of zinc serves two purposes: firstly it covers the iron and prevents its oxidation (rather like a coat of paint) and secondly it provides anodic protection.If the galvanized steel is scratched, allowing the air to oxidize some iron, the Fe2+ produced is immediately reduced to iron by the zinc, and rusting does not occur. Similar application in which one metal is sacrificed to protect another are the attaching of sacrificial blocks of magnesium to underground steel pipelines and the hulls of ships to prevent the rusting of iron.Reduction Potential DiagramsThe reaction and stability of the various oxidation states of an element can be shown by the appropriate half reactions and reduction potentials. Consider iron: This information is consolidated into a single diagram, in which the highest oxidation state is written at the left, and the lowest state at the right.From the potentials it is apparent that reduction of FeO42- to Fe3+ releases a lot of energy, so FeO42- is a strong oxidizing agent. Similarly, Fe3+is a weaker oxidizing agent going to Fe2+, but neither Fe3+ nor Fe2+ has any tendency to reduce to Fe.Standard electrode potentials are measured on a scale with Since hydrogen is normally regarded as a reducing agent,reactions with negative values for E0are more strongly reducing than hydrogen, that is they are strongly reducing. Materials which are generally accepted as oxidizing agents have E0 values above +0.8 volts, those such as Fe3+→Fe2+of about 0.8volts are stable (equally oxidizing and reducing), and those below 0.8 volts becoming increasingly reducing.At first sight the potential of -0.4V for Fe3+→Fe2+seems wrong since the potentials for Fe3+→Fe2+ , and Fe2+→Fe are 0.77 V and 0.44V respectively. Potentialsare not thermodynamic functions, and may not be added, but the potential may be calculated from the free energy G, using the equation △G=-nfE0where n is the number of electrons involved and F the Faraday.The reduction potential diagram for copper in acid solution is oxidation stateThe potential, and hence the energy released when Cu2+ is reduced to Cu+areboth very small, hence Cu2+ is stable. On moving from left to right the potentials Cu2+→Cu+ →Cu become more positive. Whenever this is found. The species in the middle (Cu+ in this case) disproportionates , that is it behaves as both a self-oxidizingand a self-reducing agent because it is energetically favourable for the following two change to occur together.Thus Cu+ disproportionates in solution, and is only found in the solid state.Lesson 4 Introduction to Organic Chemistry1.Sources of Organic CompoundsThe major sources of organic chemicals are coal, petroleum, and agricultural products.Both coal and petroleum were formed through the geologic processes of changing animal and plant remains into carbon-containing residues. About one-third of all organic chemicals are derived from coal and about one-half from the petroleum industry.2.The Methods and Objectives of Organic ChemistryBecause of the tremendous number of organic compounds known, and of themany more being synthesized daily, the study of organic chemistry is not the studyof individual compounds, it is the study of groups or families of compounds allclosely related to each other. Obviously, the former approach would be prohibitive.Once the structural relationships of certain typical members of a particular groupor family of compounds are understood, these structural features are understoodfor any one of the many members of the family, even though some may not beknown compounds. For each group or family of compounds often called homologous series of compounds, structural features are important. In studying organic chemistry, it is not enough to know the identities of the elements and how many atoms of each element are present in a given molecule. More importantly, the order in which these atoms are linked together to form the molecule must also be known. Once the identities of the elements and the number of atoms present in each of these elements have been established, structural studies are quite important. They require considerable effort and ingenuity on thepart of the organic chemist.Another important phase of the study of organic chemistry is communication, or exchange of information, among organic chemists. This requires the acquisition of adequate vocabulary and terminology so that any one of the more than a million known compounds, or any one of the yet unsynthesized compounds, can be discussed intelligently on an individual basis. This requires a highly systematized method of naming organic compounds. This science of nomenclature has received considerable attention during the development of organic chemistry, and it will constitute a second important topic for consideration in connection with each homologous series of compounds to be studied.A third important topic for consideration in connection with each homologous series of compounds is procurement. Many organic compounds, as pointed out earlier, are naturally occurring. Many others, however, are not found in nature, and must be synthesized or prepared from compounds which can be obtained from natural sources. The term“synthesis” means building up of a molecule from smaller units. It is more often used, however, to mean the chemical process of changing or converting an available compound into the desired compound, either in the laboratory or on a larger scale, as in a manufacturing plant. This general topic can be described as “Methods of Synthesis”.In order that the above conversion of one compound to another may be accomplished, the chemical properties of each compound must be understood. Again, the solution of this problem would be impossible were it not for the fact that the chemical properties of a family of compounds aredocumented, thus making it possible to predict the chemical properties of any member of the family, even though a particular member may not be a known compound. This phase of studying each family can be entit led “Chemical Reactions” or “Chemical Properties”.Another important phase of studying organic chemistry concerns the physical properties of organic compounds. Physical properties are particularly important in predicting the usefulness of a particular substance for a specific purpose. For example, a compound that is a gas at normal temperature and pressure is not likely to be a good bearing lubricant. Physical properties of organic compounds are important to the beginning organic student, but to a lesser extent than the other four topic, namely, (1) Structure, (2) Nomenclature, (3) Methods of Synthesis, and(4) Chemical Reactions.For convenience, and again based on tradition, organic chemistry is divided into two parts, aliphatic compounds and aromatic compounds. The term “aliphatic” has its origin in the Greek word Aleiphar meaning fat. Many fats are members of the general class of aliphatic c ompound. The term “aromatic” is applied to the benzene derivatives because certain of these compounds have unusually pleasant odors. The term“aromatic” has a broader meaning today.The objectives of the science of organic chemistry may then be defined as follows: (1) to provide mankind with information concerning the nature, origin, and transformations of organic matter, and (2) to provide the necessary knowledge and methods for the utilization of organic matter most effectively in improving the standard of living, In order to accomplish these objects, the organic chemist must also utilize the knowledge made availablethrough research in many other branches of science.3.Identification of Unknown Organic CompoundsThe chemistry of biological systems is very complicated and the organic compounds present are numerous and constitute complex mixtures. Consequently,isolation of a pure chemical species from any one of the major sources of organic matter requires elaborate and painstaking isolation procedures. Therefore, a major portion of the effort of organic chemists over the years has been devoted to improving methods for isolation and purification of organic compounds. Isolation proceduresIsolation procedures are usually followed by the application of certain criteria of purity to the compound isolated. The chemist must establish that the isolation procedure has resulted in the elimination of essentially all of the “foreign” molecules from the compound, and that he is dealing with a single molecular species. Consequently, criteria of purity become very important. These steps are followed by the application of both qualitative and quantitative analytical techniques to identify the elements present in the compound and the ratio of these elements to each other. From these data, an empirical formula can be determined. The empirical formula is defined as the formula that shows the kind and ratio of atoms present in the molecule, but not necessarily the total number of atoms present, This step must be followed by the establishment of the molecular formula for the compound. The molecule formula is defined as the formula that shows the number of atoms per molecule, as well as their kind and ratios. One of the several known methods of determinating molecular weights must be applied in order to establish the molecular formula. The molecular formula is eitherequal to or some multiple of the empirical formula. The molecular formula is therefore established as that multiple of the empirical formula which most closely coincides with the determined molecular weight.As was pointedAs was pointed out earlier, in organic chemistry as well as in many branches of inorganic chemistry, it is not sufficient to know which elements and how many atoms of each element are present in a given molecule. The order in which these atoms are linked together to form the molecule must also be known. Extensive chemical and physical methods for establishing the order in which atoms are linked together have been worked out. Applications of appropriate procedures ofthis type lead to the proposal of a structural formula for the compound.The assignment ofThe assignment of a structural formula of a compound on the basis of its physical and chemical properties does not conclusively establish its structure. Further confirmation must often be obtained as the result of an unambiguous synthesis of the compound. Methods of synthesis useful both from the standpoint of structure proof and from the standpoint of converting a given compound to another will be treated in this text. If all of the physical and chemical properties of the synthetic compound are identical wit those of the isolated compound, the proposed structural formula is considered to be correct.In summaryIn summary, the following four steps are required in order to completely identify any organic compound isolated for the first time from a natural source or produced for the first time in thelaboratory:(1)Isolation of the compound from the mixture of organic or inorganiccompounds among which it may be found, followed by application of appropriate criteria of purity.(2)Establishment of its empirical and molecular formulas by use of appropriatemethods of qualitative analysis, quantitative analysis, and molecular weight determination.(3)Proposal of a structural formula as the result of appropriate chemical andphysical examination of the compound.(4)Synthesis of the compound by an unambiguous method as confirmation ofthe proposed structural formula.Concern1. (不用被动语态)关于2. 涉及,关系到;影响到The letter is chiefly concerned with export commodities.这封信主要是关于出口商品的。
