The Tao of Chemistry E. R. Scerri M.P.W. College, 24, Elvaston Place, London SW7,United Kingdom A few years ago a thought-provoking book entitled "The Tao of Physics" was published and seems to have developed something of a cult following ( I ) . I t draws a number of oarallels between Eastern ohilosonhv and the discoveries of modern physics, claiming 'that thk paths to knowledge are essentially complementary and arrive a t similar conclusions. The field of chemistry has, however, been largely ignored in this respect, and yet i t lends itself to a closer analogy with the basic Eoncept of coexistence of opposites, found &icularly in Taoist thought (2).Moreover, this aspect of Chinese ohilosonhv offers i n ideal and humanistic~frameworkfor teaching elementary chemical concepts. I t is not the intention of this article t o discuss whether or not such analogies have any validity or mystical significance. The author merely wishes to use the analogy even if i t may only be superficial, todraw attention to aunifyingconcept in chemistrv that is usuallv taken for . granted or simply . . implied. Considering important topics such as atomic structure, bonding, organic reaction mechanisms, acid-base equilibria, and redox reactions reveals that they all hinge on the coexistence of opposites. Likewise the ancient Chinese texts tell us that relative values such as good and evil, light and darkness, etc.. are not trulv. oooosed but comulementarv. .. .. in that eacb depends on its opposite for its very existence. The iuxtaoosition of onnosite aualities is seen to aive rise to dive;sity in creation, A d the dise person is he or she who can reconcile the annarent conflict of opposites both within his or her own beingand the external world.
..
Under heaven all can see beauty as beauty only because there is ugliness. All can know good only hecause there is evil. Therefore having and not having arise together Difficultand easv comolement each other. Long and short contra&each other. High and low rest an each other. Voice and sound harmonise each other. Front and back follow one another. Therefore the sage goes about doing nothing, teaching no talking. (3)
In chemistry we find the coexistence of opposites on various interpenetrating levels. For example, the neutral atom consists of eoual numbers of nositive urotons and newtive electrons. The occurrence of a charge imbalance, or ionization. mav lead to chemical reaction and bondine between the elements. Positive sodium ions bond to neg&ve chlorine ions, the key factor responsible for the bonding being the coexistence of oppositely charged ions. The two ions are also complementary in that they eacb achieve a stable octet as a resuit of electron transfer.~lementsthat most easily form positive ions are termed metallic while those forming negative ions constitute the nonmetals. This distinction orovides another important aspect to classify both chemical and physical properties of the elements. Furthermore, the periodic table of elements may be broadly divided into metals and nonmetals lying at opposite sides of the table. Although we have been discussing ionic bonding, the vast maioritv - - of compounds are based on covalencv and do not, therefore, depend on the formation of oppositely charged ions. The chemistry of covalent compounds does, however, contain elements of polarity as seen in the mediation of electrophiles and nucleophiles in reaction mechanisms. Al-
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106
Journal of Chemical Education
kenes, for example, typically show electrophilic additions, as in the attack of the electron-rich double bond by partially positively charged bromine atoms. Elements of polarity even exist within these reactions, since the initial electrophilic attack creates a positive site on the neighboring carbon atom, providing a point of nucleophilic attack by, for example, a negative bromine atom. Returning to a passage from Lao Tsu's writing on the Tao we find (4) That which shrinks must first expand. That which fails muat first he struna. That n hich is rast down must first he raised Before receiving there must first be giving. This is called preception of the nature of things. As many writers have pointed out, it is difficult for Westerners to comprehend fully that these polar opposites are extremes of a single whole concept (5). Perhaps the readily acceptable chemical examples of com~lementaw - onoosites .. could conversely clarify the essence of Taoist thought for us. Another such chemical example is orovided bv the nature of acids and bases. At a very-elementary level an acid is presented as a nonmetal oxide solution, which in aporooriate quantity and concentration will neutralize a base consisting of a metal oxide or hydroxide. More precise definitions are eiven bv the theories of Arrhenius. Bronsted and Lowry, a& ~ e w i s . The Arrhenius treatment considers acids as substances producing hydronium ions in aqueous solution while bases form hvdroxvl ions. The neutralization occurrine between an acidand base may therefore be essentially represented as ~
~
.-
~
a
HsOt
+ OH- = 2H20
According to the Bronsted and Lowrv theorv. an acid is anv substance which may denote protons while-its polar opposite, a base, is seen as a proton acceptor. The Lewis scheme. on the other hand considers acids t o be electron acceptors and bases as electron donors. Clearly, whichever drfinition one adheres to, acid-base equilibria are found to oprrate via the coexistence of oppositccnrities. Similarly the subject ofoxidationand reduction may l ~ ediscussed through various approaches, all of which show this same analorv with the Eastern , .ohilosu~hicalnotion of complementary poles. On the simdest level an oxidizine aeent can be described as a substance that introduces oxygen into an element or compound, whereas a reducing agent performs the opposite role of removing oxygen. A more systematic definition consists in assigning oxidation numbers to all atoms in a reaction and regarding an increase in this quantity as an oxidation and a decrease as a reduction. Alternatively, oxidation is defined as a loss of electrons while reduction involves their being gained. Generally, reductants are metals while nonmetals and their ions act as oxidants, thus maintaining a link with the basic chemical polarity described at the outset. We therefore see that maior areas of chemistrv . mav. be viewed as the action of opposite but complementary tendencies. These properties may be linked with other polar oooosites such as metals and honmetals and further-reduced to complementary aspects of charged elementary particles
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within the atom. I t would seem that this feature of complementarity, running through various levels of chemical reactions, may be usefully adopted as a starting point or philosophlcal background on which to base a more detailed account of the subject. Needless to say, the essential aspect from the pedagogic ~ o i n of t view lies in the coexistence of opposites itself and not its disputable links with Eastern mysticism. Any reader who might object to this latter feature could nevertheless retain the essence of the analogy in order to present the basic chemical concepts discussed in this article as well as many other concepts. Finally a passage from the Indian classic, "The Upmishads," which illustrates that the philosophical view attributed here to Taoism is by no means confined to China alone (6).
The one Self never moves, yet is too swift for the mind. The senses cannot reach It, It is ever heyond their grasp. Remaining still It outstripa all activity, Yet in It rests the breath of all that moves. It moves, yet It moves not, It is far, yet It is near. It is within all this, And yet without all this. Literature (1) Capra. F."TheTsoofPhyaics"; Fontans: London. 1976. (2) peng,G.; E ~ ~ IJ . -~Ts~ O ~T~ , ching..;wiidvood ~
nouse:
(3) Ref2,ChapZ.
~1973. ~
d
~
~ ~ ~ , ~ ~ ~ ~ P a y e h ~ t h h h h PWe Y E&.a.; sPenguin:London, tand 1961.
(6) Russell, P.; Shearer, A., Trans."The Upmiahads";Wildvoad House: ond don. 1978.
Volume 63
Number 2
February 1986
107
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