Michael Hudson University of Reading Whiteknights, Reading RG6 2AD
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Why Should We Teach Descriptive Chemistry?
The purpose of this paper is to deal with some serious trends which are arising with respect to the decreasing amount of descriptive chemistry which is being taught in chemistry courses both a t the secondary and tertiary level throughout the world (1-3). T h e paper deals initially with adefinition of chemistry and then considers areas of concern of descriptive chemistry and compares these with a definition of chemistry. Modern trends in some svllabuses are considered. It is s u e gested that n)te learning oi'oversirnplified theoris is replacing the learning of meanincful and factual material. It is suggested that not or& is t he ov&emphasis on theories a puor ad&)ach to teachine. chem~strv,hut alro it createlipeat difficulties with respect to-students-who are trying to learn the language of chemistry. A course is suggested in outline, and general and specific aims are mentioned. Some detailed examples of models of thought, which should replace theories, are sugeested and the future of svllabuses is discussed brieflv. . "~ The area; of concern of descriptive chemistry have been summarized neatlv bv Eurene Hochow in his buuk "Modern Descriptive ~ h e m k t i y "(i). ~
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Descriptive chemistry is concerned with the chemical elements and the compounds they form with each other. It is also concerned with the energy lost or gained when such combinations of elements occur. It is important to compare these areas of concern of descriotive chemistrv with a definition of chemistrv which was produced by ~ y h & nand others (5,6). Chemistry is the integrated study of the preparation, properties, structure, and reactions of the chemical elements and their compounds, and of the systems which they form. The close parallel between the areas of concern of descriptive chemistry and o i the definition of rhemistry are by no means coincidental. Descriptive chemistry is roncerned with the basic and fundamental aspectsof chemistry. It is important, surely, for syllahuses which purport to tie tearhing or roncerned with chemistry to contain a constderable proportion of descriptive chemistry.~lthoughsuch a statrment niay seem obvious, modern syllabuses have tended to restrict the amount of descriotive chemistrv to an absolute minimum. Moreover. syllabuses are tending more and more to put theories before the annronriate exneriment and then are a t t e m.~ t i .. n eto use .. rarefully selected experiments to prove or illustrate the theory. Thus one finds in some syllahuses statements such as
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Mechanisms of organic reactionsSN1 and SN2 mechanisms illustrated by experiments. However, are the rurriculum developers aware that notations such as S N l and SN2 are rapidly going out of use? It seems that they are introducing theories into syllabuses at a time at which they are going our of favor with research workem. Hoc much better for everyone concerned if they would introduce chemistry properly through descriptive chemistry. This means putting experiments before the non-theoretical work. In the United Kingdom the Association for Science Education has issued a discussion document in which different proposals are put forward for teaching science in secondary schools. 'l'he title of the document is 'Alternatives for Science Education" ((0. Although there is much that one can criticize ahout this ducument, they do emphasize that there i s a need 770 1 Journal of Chemical Education
The Top Flny Chemicals
Sulbricacid
Carbon dioxide, ail forms
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Ethylene oxide Ammonium sulfate Carbon black Ethylene glycol Butadiene(t.3-),rubber grade
Oxygen, high gas
purity
sodium hydroxide
sodium
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Pnosphorrc acid. total N Ificacid Ammonium nitrate Propene Benzene
1.2.dichlwoethene Urea, primary solution
Toluene, all grades Ethylbenzene Styrene Methanol, synthetic Fwmaldehvde. 37% by weight Xylene, all grades Vinyl chloride Hydrochloric acid Terephthalic acid Ethylene Nitrogen, highand low purity
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Cumene Acet~acrd, rynthstic Scdium sulfate Calcium chloride Phenol. synthetic Aluminium sulfate Cyclohexane Acetone Propme oxide lsoprapyi alcohol Adipic acid Acrybitrile Vinyl acetate Scdium silicate Acetic anhydride Titanium dioxide Scdium tripolyphosphate Ethanol, synthetic
to simplify and to reduce the total content of advanced courses in biology, chemistry, and physics. This view is held by many teachers of chemistry in this country. Modern courses place a great emphasis on abstract concepts to the detriment of descriptive chemistry. Is it therefore feasible to reduce the amount of time spent on oversimplified versions of difficult concepts and to increase the amount of descriptive chemistry? Would such a change produce a simplification and a reduction in the total content of advanced courses in chemistm? In trying to answer such questions, one is tempted to turn to educational theories to find some form of iustifiration. Indeed. there is a large amount of well-supported work which doe$ lend suDoort to such an idea. However. i t is necessarv to ooint out that' there are statements which have been made by leadine. educationalists which can be misconstrued t o i m ~ l v that one can teach advanced concepts without a proper emphasis on the reactions of chemicals. A famous statement (9) has been made by Bruner: Any idea or problem or body of knowledge can he presented in a form simple enough so that any particular learner can understand it in a recognizable form. This statement may he taken to imply that one can reach the finer points of kinetics, equilibria, structure, and energy rhanges to eleven year olds! This is, however, not what the author is implying and should not be taken ax a justification for attempting to introduce oversimplified ( 1 0 ) versions of elegant hut abstract theories. More useful in the context of educational research is the work which was done bv Piaeet and bas now been developed by Shayer (11,12). liveribroad terms, this work lends suooort to the idea. which manv chemistry teachers have ahlady, namely, that it is important to deal with concrete or real situations ( I 3 ) before going on to consider the related more ahntract ideas. This is, of course, just what onedoes by introducing~xperiment.aandchemical
reactions hefore going on to deal with theories or models of thought. In manv wavs one of the worst thines that we can do (14,75)for our students is to go straight intoconcepts without giving them the proper foundation on which to build their ideas. Einstein, for example, has indicated that if one introduces a concept, one is hound to use the language of that concept. There is a further difficulty that our language is compelled to work with words which are inseparably connected with those primitive concepts (16). Indeed if one looks a t the concents which we teach in chemistry, one can see that the language level of the concepts is extremelv hieh. Often the abstract cmceDts lead to a language-levelkhiFhis too high for most of our students. And yet if we are .. eoine.. to introduce a course on chemistrv with a proper emphasis on descriptive chcmistry, it is important to take note the critia of such an approach. Henri I'oincari., who was a nineteenth century mathematician, gave this statement which is of course still true today: Science is built up with facts, as a house is built up with stones, hut a collection of f a d s is no more science than a heap of stones is a house. Most of us recognize that sciences are not mere catalogues of materials that can he used in trade. because thev are svstems or symbols of great ideas that may he used to exercise reason and to feel the imagination. Nevertheless, these great ideas should he introduced properly and carefully. I t is important t o ensure that there is not a return to the situation in which students who do well in elementary chemistry courses are those who memorize all the material and regurgitate for the examination. Descriptive chemistry is much mire than this because i t provides a thorough grounding in experimental chemistry and in the reactions of the elements and their simple compounds and provides a clear link to models of chemical thought. A course with a proper amount of descriptive chemistry will be academically respectable only if it does not depend on rote learning of useless facts. But memorization of theories can be just as useless, and a rigid adherence to theories has in the Dast held un the nroeress of science. Dalton's atomic theory; for example, hindered an understanding of structure in the late nineteenth century. Adherence to the octet rule, arguably hindered the advancement of noble gas chemistrv because there was a clear implication that the noble gases would not react. The theor; of perfect reeularitv in crvstalline solids hindered an understanding 2 the s&engthbf materials. Consequently, whatever theories are introduced into advanced level courses, the student should be encouraged to have a flexible attitude to the theories and should acrevt that the experimental facts have the ring of truth. In some cases incorrect theories have been introduced. Although the theory of hyhridization is not specifically mentioned in some syllabuses, there is no doubt that many teachers place a considerable emphasis on this theory to teach the structure of molecules. Many of the textbooks, however, contain manv errors in the wav that thev present the theory. This is not jlst a question of oversim&kcation of a theory, hut it is a clear wav in which manv authors misunderstand the theory. There is danger, more&er, that the hyhridization theory is going to be introduced into schools a t a time when i t is being discredited by many research chemists. Clearly, one cannot remove all theory from courses, hut it is important to ensure that those theories which are necessary are introduced a t the right level and are preceded, wherever possible, by well-selected experiments, or alternatively well-chosen examples from descriptive chemistry. There are clearly some guidelines which would help us in selecting the theories which one ought to introduce into school svllahuses. Oversimnlified versions of elegant and abstract theories should he removed ~ h e r e v e r ~ o s s i band l e should be
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replaced by models of thought which can he introduced a t the right intellectual level. The mathematical difficulties should he simplified wherever possible. The students should he able to see the assumptions which the theory makes and to see the advantages and disadvantages of the theory. Suitable models of thought which can he introduced into schools include the electron pair repulsion model t o explain the structure of simple molecules, the chemistry of functional groups in oreanic chemistrv: - . the concent of oxidation numbers: the concept of electronegativity. The notion of energy levels within atoms and molecules is such an important idea that it ought to be introduced toward the end of many courses provided the students are coping with the basic chemistrv. Students also should he show^; the difference between somi of the concepts which chemists use. Elecrroneaativitv is essentially a chemat's approximation as to what m-ight be the case in molecules. Ionization energies, however, are precisely measured quantities. Chemistry is such an important science and plays sucha key role in the everyday lives of people in developed countries that it is unfair to students w place an undue emphasis on thwries because this will detract from the emphasis which can he put on presenting chemistry as a branch of knowledge worthy of study as a part of a preparation for life. Students should he led to understand the role of chemical science in the society in which they live. Why is it, for example, that many of our moderncoursei fail togive a proper emphasis to the top fifty chemicals which are produced by most developed rountries? The chemistry of some of these chemicals is admittedly quite cwnplex, hut most of these have chemistry which is not too difficult for colleee students to understand. The rhemistw of these compound: might form a central part of all chemikry courses. If one leaves out the basic chemistry of these chemicals how can the syllabuses claim to he relating chemistry to the everyday lives of students? Chemistry throughout the history of mankind, has played a key role in the development of our civilization (17). I t is important, therefore, to enable students to appreciate that chemistry is the product of the work and thought of many people and that the history of chemical discovery and thought is closelv linked with a social history. Very interesting case studies could be produced by a look a t the social history of lime, sulfuric acid, nitrates, phosphates, and carefully selected . . metals. Above all, pupils should be encouraged to use the experimental annroach to solvine nrohlems. This will enable them to develo'dthe ability to a&;eciate that they need to produce a body of evidence before making judgments. Students should he encouraged to develop the capacity to accept evidence contrarv to established beliefs. This acceptance of contrarv evidence cannot be achieved if theories are introduced before experiments. Dalton, himself. chose to reiect anv exveriment which did not agree with his atomic theoiy. A g;od i n d welltrained chemist must have a flexihle and udaptahlc approach to modern theories. In many countries, however, it ii important to realize that there is a very restricted amount of exnerimental work that is done in schools. Nevertheless. where possible, experiments should be introduced to enahle students to have an anoreciation of the chemicals that one is talking about. They %odd appreciate that silver bromide is not a r e i gas and that copper sulfate is not a blue liquid! Much of the appeal of chemistry surely lies in the fact that there are manv areas of uncertaintv where scientists mav differ on of interpretation. There are and always have been controversies emphasized to students. Chemistrv is a living and rapidly developing science, and there are man; unresolved problems which could he introduced a t the right level for students. For example, companies are still looking for simple and cheap methods to separate cobalt from iron. They are still looking a t complexes which will combat cancer. I t is interesting that one of the most efficient chemicals that combats cancer is one of the simplest platinum compounds.
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Volume 57, Number 11, November 1980 1 771
One final plea that I would make is that chemical ideas should be introduced singly. All too often students complain that in modern syllabuses, including Nuffield A-level chemas reaction istry, that they are introduced to ideas mechanisms and the properties of functional groups at the same time. Indeed an understanding of the basic chemistry o f the f u n c t i o n a l groups relies upon an understanding o f the reaction mechanisms which many of them fail to do. It is important, therefore, to investigate methods of introducing descriptive chemistry (18) before going on to do the more thenretical interpretation. Literature Cited (1) Hudaan, M. J., Chrm Brit.. 14,468 (1978). (21 Bray. S. V. P.. Chsm. Brit.. 14,331 (1978).
772 1 Journal of Chemical Education
(3) New Directions in the Chemistry Cumiculum, Praeedings of an ~nternstimalconference, McMsator Uniueaity, June 1978. (4) Rachoa, E. G.,..MademDesniptiveChemistry.'.Ssundem, 1977, ( 5 ) Hammond.G., N y h o h , ~ . ~J. . ,CHEM. EOuC.,48,6 (1971). (6) Nyholm. R.S..J. CHEM. EDUC.. 48,30(1971). (7) ..~iternstiuwfor ~ c i e n c c~ducstion: h i a t i o n for science duea at ion, (u.K.), 1978. (81 Bruner, J. s., he p r e s s of ~ d ~ ~ a t i o ~ n .s "r v a r dunivemity press. ~ E J . (9) Gillespie, R. J., Chom Cm., 28,23 (1976). (10) s h s y e r . ~ . , ~ a c h e m a n n .E., ~ . w y l a m , ~ .B, I ~J~E. ~ .P W ~ O ~46, . , (1976). (111 lngle,R.B.,Shayer,M.,Edue. in C h m . 8,182 (19711.
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~ , ~ ~ ~ ; , ~ O ; Educ,, , ~ j 61 ~ ,1974), ~ ~ ; i i (14) Fensham, P. J., in '"NewMovements in the study and ~ e a ~ h i ~ ~ ~ f c hD. ~J. ~ i ~ t ~ , ' . Daniels ( ~ d i t o r )~ernpiosmith, , 1975. p. 199. (15) Schilp, P. A.."AlbertEinstein: Philosopher-Scienti8t:Csmhridge Univeaity Press, znd ~ d . 1952. , (16) Singer, C., "A Short History of Scientific ldeas to 1900." Oxford. 1959 (reprintd 1977). (17) Kornhsuwr.A..Eur. J Sci. Edue., 1,21(1979).
