Elective affinity

This compound, which contains atoms arranged tetrahedrally around the boron atom, can readily be isolated from a mixture of dimethyl ether and boron trichloride. On occasions a chlorine atom, in spite of its high election affinity, will donate an electron pair, an example being found in the dimerisation of gaseous monomeric aluminium chloride to give the more stable Al2Clg in which each aluminium has a tetrahedral configuration ... 

Wahl-recht, n. suffrage, franchise, -sprucli, m. motto, device, -verwandtschaft, /. elective affinity congeniality. 

Reilly, Terry. Alchemy, chemistry and literary form in Goethe s Elective Affinities. Cauda Pavonis 16, no. 2 (Fall 1997) 1-9. 

The very term elective affinity must lead into error, as it supposes the union of the whole of one substance with another, in preference to a third whereas there is only a partition of action, which is itself subordinate to other chemical circumstances,. . . care must be taken not to consider this affinity as a uniform force which produces compositions and decompositions.. . . Such a conclusion would lead us to neglect all the modification which it undergoes from the commencement of action to the term of equilibrium. 51... 

Holmes, Frederic L. "From Elective Affinities to Chemical Equilibrium Berthollet s Law of Mass Action." Chymia 8 (1962) 105146. 

At the start of Goethe s Elective Affinities (1809), Charlotte and Eduard are alone, hermetically sealed, we might say, in a functional but passionless marriage (perhaps functional passionless). Having married late, they... 

Goethe, Johann Wolfgang von. Elective Affinities Wahlverwandtschaften). Translated by David Gonstantine. Oxford Oxford University Press, 1994. 

Electron affinity is conventionally defined as the energy released when an electron is added to the valence shell of an atom. Unfortunately, this is in contradiction to the universal thermodynamic convention that enthalpies of exothermic reactions shall be assigned negative signs. Since it seems impossible to overthrow the election affinity convention at this late date without undue confusion, one can adopt one of two viewpoints to minimize confusion. One is to let the electron affinities of the most active nonmetals be positive, even though in thermodynamic calculations the enthalpies are negative ... 

Ar. Ns This detector employs a source of P radiation (usually 6JNi-cf. helium ionisation detector). The 1000-10.000 velocities of the high energy electrons are reduced to thermal velocities by coOisioo with atoms of inert gas with which the detector chamber is purged. When a sample of a gas with a greater election affinity than the inert gas is introduced into the ccC some of the electrons are captured and form negative ioas. 

It is a sort of molecular sociology Non-covalent interactions define the intercomponent bond, the action and reaction, in brief, the behaviour of the molecular individuals and populations their social structure as an ensemble of individuals having its own organisation their stability and their fragility their tendency to associate or to isolate themselves their selectivity, their elective affinities and class structure, their ability to recognize each other their dynamics, fluidity or rigidity of arrangements and of castes, tensions, motions and reorientations their mutual action and their transformations by each other. 

Different elective affinity of elements as compared to carbon. Electropositive elements (Si, B, AI, P) have a considerably larger affinity to electronegative elements than carbon. In other words, silicon, boron, aluminum, phosphorus and other elements form weaker bonds with electropositive elements (H, Si, B, Al, As, Sb, Bi, etc.), and stronger bonds with electronegative elements (O, N, Cl, Br, F, etc.) than carbon. 

It has to be remarked that by making this correction, a reasonable approximation to a constant external potential, necessary for the calculation of electronegativity and hardness, is obtained. An analogous reasoning was followed for the electron affinities. Using the ionization energies and election affinities obtained in this manner, AIM electronegativities and hardnesses were calculated. 

Fig. 1 Rene Magritte, Elective Affinities (1933) - oil on canvas. Private collection...

Fourcroy was keenly aware, then, of the limitations of the princi-palist approach to composition embedded in the phlogiston theory. Not only did he point out the mismatch between the supposed presence of phlogiston and the manifested properties of the bodies containing it he also explicitly criticized the Stahlian hierarchy of composition as a mere imagination. Instead, he wished to introduce a classification of chemical experience based on affinities. In other words, he sought to work out the affinity approach to composition in chemical systematics. This is why he later fought to preserve the doctrine of elective affinities in opposition to Berthollet. Although historians have interpreted Fourcroy s work as a contribution to the study of composition, his works should be placed within the framework of affinity chemistry which called for a new order of chemical composition and systematics. 

At the classificatory or theoretical level, various affinities corresponded to different categories of chemical actions or combinations. Elective affinity referred to the displacement reaction of a salt by an acid complex affinity referred to the double displacement reactions of two... 

In particular, Berthollet wished to demolish the conception that elective affinity could be measured by complete displacement reactions without taking into account the quantities of the respective substances. Displacement reactions necessarily produced a partition of the acid between the two competing bases, the proportion of which was controlled by their respective quantities as well as by their affinities. That is, a weaker degree of affinity could be compensated by an increase of quantity ... 

That Berthollet opposed the method of determining the affinity specific to each pair of substances rather than the notion of such absolute affinity can be seen in the following argument. He maintained that it was impossible to determine elective affinity, even if one reinterpreted the concept according to his idea, acknowledging the fact of partition and the role of quantities ... 

To ascertain the elective affinity of two substances for a third, according to our idea of that term, it will be necessary to determine in what proportion that third substance divides its action between the two former, and the degree of saturation which each of these two can attain when they act in competition-, their respective affinities will be commensurate with the degree of their saturation, which degree of saturation must be still further influenced by the quantity of each which acts so that if these quantities were equal, the degree of saturation would be the exact measure of the affinity. ... 

In order to make the measurement of elective affinities meaningful, Berthollet deemed it necessary to keep the quantities of two substances equal not only at the beginning but also at each successive stage of reaction, which was practically impossible. Maintaining the same proportion... 

The very term, elective affinity must lead into error, as it supposes the union of the whole of one substance with another, in preference to a third whereas there is only a partition of action, which is itself subordinate to other chemical circumstances. ... 

Not only was elective affinity inadequate as a means of comparing the affinities of different substances it also led to critical and pervasive errors in chemical analysis by compromising the purity of chemical substances obtained in this manner. In other words, the supposition of complete displacement reactions encouraged the use of impure substances as pure ones in chemical analysis, which seriously compromised the accuracy of chemical analysis. Chemists were deceived, for example, in believing that they could obtain pure magnesia from displacement reactions. Berthollet s pointed attack on the notion of elective affinity is understandable in light of the fact that it caused a serious problem for the validity of basic chemical analysis. His attack was quite successful in undermining chemists naive confidence in the absolute order of chemical affinities obtained from displacement reactions and in the analytic purity of the substances thus obtained. He discredited affinity tables as mere memorandums of barren facts ... 

As Holmes and Le Grand have pointed out, Berthollet did not abandon the notion of selective affinity specific to each pair of substances in proposing the notion of chemical mass. In the above quotation, he used affinity in the sense of a selective force between different substances. More often, however, he conveyed this sense by using the term intensity of affinity or energy of affinity. It was the general law to which chemical action is subjugated that the substances exercise in the ratio of the energy of their affinity and of their quantity. Berthollet did not object, then, to the sense of selectivity he objected to the sense of false absoluteness that the notion of elective affinity conveyed. He criticized the perception that elective affinity conceived and measured via dis-... 

The doctrine of Bergman is founded entirely on the supposition that elective affinity is an invariable force, and of such a nature, that a body which expels another from its combination, cannot possibly be separated from the same by the body which it eliminated. Such was the certainty with which elective affinity has been considered as an uniform force, that celebrated chemists have endeavored to represent by numbers, the comparative elective affinities of different substances, independently of any difference in the proportion of their quantities. 

It is my purpose to prove in the following sheets, that elective affinity, in general, does not act as a determinate force, by which one body separates completely another from a combination but that, in all the compositions and decompositions produced by elective affinity, there takes place a partition of the base, or subject of the combination, between the two bodies whose actions are opposed and that the proportions of this partition are determined, not solely by the difference of energy in the affinities, but also by the difference of the quantities of the bodies so that an excess of quantity of the body whose affinity is the weaker, compensates for the weakness of affinity. 

Berthollet s critique effectively destroyed the loosely correlated usage of elective affinity as a category of reaction, the cause thereof, and an analytic method of determining relative affinities of acids and bases. One could still use it as a category of reaction in which an acid reacted with... 

Berthollet reasoned that such an exchange of bases did not take place because the partition of acids and bases was in effect. When the exchange did occur, it was due not to the affinities in action, but to other real causes such as crystallization and precipitation. Chemists had inadvertently ascribed the strongest affinities to the substances that precipitated easily. Other causes, such as heat and efflorescence, also contributed to the outcome of complex affinities, as was the case for natron. In short, elective affinity involved an unsaturated substance, while complex affinities worked between saturated substances. The notion of elective affinity was tightly bound to the analytic procedure in which two acids, one combined in the salt and the other free, had to compete for the common base. 

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