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INORGANIC CHEMISTRY FOR THE CHEMISTRY MAJOR W. CONARD FERNELIUS The Pennsylvania State College, State College, Pennsylvania
INORGANIC chemistry should have a place in the training of the chemistry major because the inorganic field embraces so large a portion of the total knowledge in the science of chemistry. Let me remind you that there are a t least 91 elements in the earth's crust which can be isolated in detectable amounts. Further, there are a t least five more elements which can be synthesized. Each of these has a distinct set of properties and behavior. No one can speak of having a complete basic understanding of chemistry until he has a t least a speaking acquaintance with each of these elements. Since our know!edge of most of these elements is incomplete, each presents some problems for investigation many of which are of theoretical importance. It is important that we know the elements sufficiently well to recognize the existence of these problems. The handling of inorganic substances constitutes an important portion of chemical industry. Even organic chemical reactions are often the action of inorganic substances on organic compounds. Many compounds which are both organic and inorganic are assuming great importance today. There are many industries other than the strictly chemical ones which are dependent upon inorganic materials: metallurgy, ceramics, etc. Finally, the technical importance of inorganic compounds is increasing: new developments in ceramics and metallurgy, geochemistry, catalysis, corrosion, the atomic energy program, the developments in phosphorus, sulfur, the halogens (especially fluorine), boron, etc. A lack of inorganic training will hinder future developments in these and other areas. It is significant that there has been a definite trend among those in the applied fields, for example, ceramics and metallurgy, to return to the chemist for help in solving their problems. A full understanding of inorganic chemistry isnot obtained by the usual sequence of chemistry courses: elementary, analytical, organic, and physical. The last two courses are not in question but many feel that the first two should be sufficientto impart a basic knowledge of inorganic chemistry. My feeling is that they are of help in this mat6er but alone are insufficient. Fundamentally, it seems that in the introductory course we are seeking to lay a foundation of basic chemical theory with sufficient factual knowledge to develop the theory and highlight a few outstanding chemical behaviors and uses. Certainly this alone is insufficient to he considered adequate inorganic training. Years ago the introductory course was much more completely devoted to inorganic chemistry than it is
today. Some feel that this has been an undesirable trend and should be reversed. I cannot share these views. Twenty-five years ago, there was comparatively little theoretical understanding of the fundamentals of chemistry and consequently few broad principles by means of which to present the facts of chemistry. More facts were presented because that was about all there was to present. The shift of emphasis in the elementary course is a natural consequence of chemistry's becoming more and more of a science. On a number of occasions, I have listened to excellent defenses of the thesis that qualitative analysis is the place where the facts of inorganic chemistry are taught and learned. In a great many institutions, qualitative analysis forms a part of the work of the first year in lieu of a systematic treatment of the metals. It should also be noted that an increasing emphasis is being placed on the use of qualitative analysis for a rough quantitative treatment of chemical equilibria. While I grant fully that qualitative analysis teaches many inorganic reactions and aids in gaining knowledge of the inorganic field it is not and should not be considered a substitute for a course in systematic inorganic chemistry. It is also true that quantitative analysis involves inorganic reactions. However, these are not numerous and the shift in emphasis in the teaching of quantitative analysis of recent years has been to teach less rather than more inorganic chemistry. It seems to be fairly obvious that inorganic chemistry deserves a place in the undergraduate curriculum and that the courses in introductory chemistry and qualitative and quantitative analysis are not sufficient to fulfill this need. However, I am acutely conscious that many chemists do not share this opinion. If you are not already conscious of this situation examine the offerings of a representative number of educational institutions and determine how many offer courses devoted exclusively to inorganic chemistry. Even at the risk of being accused of criticizing adversely the excellent work of the Committee on Professional Training of the American Chemical Society, I would suggest rereading the requirements for certification of an institution by that Committee. Do you gain the impression that inorganic chemistry has equal standing with analytical, organic, and physical chemistry? Earlier we granted that inorganic chemistry once constituted a larger portion of the training of a chemist than it does today. We have even mentioned some factors which contributed to this loss of emphasis. Perhaps a word about the inorganic chemists' failure t o
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stem this tide mill not be out of place. If I seem to be critical of my colleagues, please do not feel that I am claiming any immunity for myself. I n so far as there is criticism I must shoulder my full share of it. I t is my feeling that inorganic chemistry lost its place in the curriculum because it failed to be the challenge to the student that it should have been. I have never felt that a rehash of elementary chemistry nor an encycle pedic listing of chemical reactions could be very stimulating to the student. Is it any wonder that few students realized the challenge of the field and entered it? The situation is all the more regrettable because, during this period of stagnation of the upper-level course in inorganic chemistry, the introductory course was undergoing eeensive study and drastic revision. How much farther ahead mmld me be if sompone had only published a really stimulating advanced textbook on inorganic chemistry? We turn now to the question of when the course in inorganic chemistry should be given. It is my feeling that it should be given in the junior year after a course in physical chemistry. I know that this is not possible in most institutions. However, I make this statement to show two things: (1) The course should be taught early enough to be of use in understanding more advanced courses and (2) the course should be taught on the foundation of certain basic principles of physical chemistry. In other words, the exact position of the inorganic course in the curriculum involves compromise and an integration with the other courses of an individual institution. The coilrse will be valuable whenever it is taught; if it comes before physical chemistry then certain foundations of physical chemistry must be given as part of the course. What constitutes the follndation upon which a co3Jrsa in inorganic chemistry should rest? There are the foundations of the introductory course: of matter, energy, classifications of matter, particle nature of matter, atomic weights, atomic number, isotopes, elements, compounds, ionization, acids, bases, and nomenclature. In addition there are several others. Of major importance among these is a clear understanding of the electronic distribution in atoms and simple ions. The more detailed this information the better, at a minimum the order of filling s, p, d, and f subshells should be clear to the student as well as the concept of orbitals and magnetic properties as related to the filling of orbitals by single electrons or electron pairs. He should also clearly understand the differences between the various types of atoms as given by Bohr: (1) all shells complete (inert gas), (2) one shell incomplete, (3) two shells incomplete (transition elements), and (4) three shells incomplete (inner transition elements). The student must also have a clear understanding of the types of forces acting between atoms and the characteristic properties of the resulting compounds. I n the treatment of intermediate types of bonds, the Fajans rules are particularly helpful. They are based on the concept of the deformation (polarization) of ions and state that an electrovalence tends to pass over into a
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covalence: (1) if the attraction between the atoms is larger, (2) if the cation is small, and (3) if the anion is large. A treatment based on relative electronegativity as influencing the partial ionic character of resonance forms is preferable if the maturity of the students permits such a treatment. I t is obvious that consideration of atomic and ionic radii must accompany this present* tion. The treatment should be carried far enough to include coordination compounds. At this point the student shollld be able to answer questions about the variation of electron affinity within a family and a period and related characteristics such as metallicity, etc.; the relative volatility, hydrolysis, solubility, conductance (molten state), color, etc., of closely related binary compounds, etc.; and the variation in acid strength of a series of hydrogen compounds H.Xn. Further, he should be aware of the need for further explanation in those cases where the expected regularities are not encountered. Inasmuch as separated or radioactive isotopes are so widely used today to obtain information about inorganic materials, some understanding of the fundamental properties of nuclei are required. This should include at least some consideration of nuclear statics, relationships between nuclear composition and types of particles emitted, packing fraction, types of nuclear reactions, preparation, concentration and separation of nuclides, and the use of tracers. The great majority of textbooks and courses present the chemistry of the elements from the standpoint of the periodic table. Thus, a consideration of the alkali metals is followed by that of the alkaline earth metals, etc. One should raise a question as to whether or not this results in the greatest amount of generalization and systematization. I t has been my experience that it does not. Actually one obtains more systematization by taking broad groups of compounds such as hydrides, halides, oxides, etc., and treating them systematically from the standpoint of the periodic table, structure, bond type, etc. In each instance, general trends should be followed, if possible, in a quantitative manner. The value of a treatment of this type becomes evident when the chemistry of the less familiar elements is considered. Even though students have been trained to make rough estimates of the properties of an unfamiliar element, there are very few of them who can begin t o approach the accuracy with which Mendeleev predicted the properties of germanium, gallium, and scandium. However, with the kind of treatment given above, a student gains experience and confidence. A study of the less familiar elements convinces him that their chemical behavior is not strange or unusual but largely that which one would expect from a detailed consideration of general trends among familiar compounds. One must not leave the subject of inorganic courses without some comment on problems, written work, and examinations. I cannot hold with those who feel that one can leave to the student the matter of how he shall acquire his grasp of the subject being taught. I am a firm believer in regularly assigned problems which are
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to he turned in, graded, and returned to the student. If one wishes to he sure that a student reviews some portion of chemistry which he has had in a previous course assign him a problem involving it. If one wishes to make certain that a student really masters some important portion of the lecture material for the week assign him problems involving those items. I wish I could refer you to a good source for problems of the type just mentioned but I cannot. Most of the really good inorganic reference hooks contain no problems. The questions in those which do, fall short of accomplishingthe aimsBet forth earlier. The questions are usually of the essay type and concerned with
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stoichiometry. The desired questions should be specific and involve the application of general trends, plotting of data, numerical calculations, etc. The working up of a set of such questions is not an easy task. Although I now have a complete set I cannot say that I have a completely satisfactory set. Over the years I have found that frequent short quizzes and at least two hour examinations in addition to the final are desirable t o give the student practice in attaining the objectives of the course and confidence in his ability to do so. I n order to gain coverage in a reasonable time, I have turned t o the simpler types of objective questions with quite satisfactory results.
