Dualistic theory

With the development of organic chemistry during the latter part of the nineteenth century the dualistic theory fell largely into disuse, because of the im-. possibility of applying it satisfactorily to the compounds of carbon, which in... 

The dualistic theory of chemical combination proposed by Davy and Berzelius, although it is not as simply and widely applicable as they had hoped, explains quite successfully in a qualitative way the formation of chemical compounds by atomic species from opposite sides of the periodic table. At the turn of the century, even before Ernest Rutherford developed the picture of the planetary atom, J. J. Thomson had suggested that the electrons are arranged in groups or layers in an atom, and that the number of electrons in the outermost layer largely determines the chemical properties of the species. 

The central tenet of Berzelius world view was the dualistic theory that still pervades our understanding of chemistry—particularly for ionic compounds such as sodium chloride. Briefly, table salt is composed of a positive part (Na ) and a negative part (Cl ). Such dualism was already part of Lavoisier s thinking some 30 years earlierd... 

Figure 3.34 Jons Jakob Berzelius (1779-1848), the great Swedish chemist and a major proponent of the electrochemical or dualistic theory. He produced elemental silicon in 1824. Silicon remained a chemical curiosity for about 60 years, until the metallurgical chemists took an interest in alloy steels. (Published with permission from the Deutsches Museum, Munich.)...

The Graham-Liebig work on polybasic acids added a fifth strand to the four interconnected developments discussed in the last section—chlorine substitution, type theory, a modified radical theory, and the hydrogen theory of acidity—all of which worked against electrochemical-dualist theory. A molecule of a polybasic acid, in Liebig s hands, was depicted as a molecular entity that could hold together additional molecular components it formed the hub, as it were, of a more complex molecule. It appears that Williamson likewise saw Graham s work on phosphoric acids in this way, for in an obituary of... 

Lavoisier had adopted the dualistic theory of neutralisation that the base and the acid (the non-metal oxide) simply combined with each other to make a salt. So, the reaction between copper(II) oxide and sulfuric acid would be ... 

For his doctoral dissertation Berzelius built a voltaic pile and studied the effects of galvanic current on patients. He found no effects (and gained no new patients), but this started a chain of thought that culminated 11 years later in a dualistic theory of chemical affinity. Berzelius followed up the experiments of Nicholson and Carlisle to find that not only did electricity split water, but it also split salts. Simultaneously with Davy, who we encounter shortly, he used electrolysis to isolate such alkaline earth metals as calcium and barium. He then proposed a dualistic theory of chemical affinity based on electrical attraction ... 

Just when the radical theory seemed to have been firmly established, a new way of looking at the reactions of organic chemistry was introduced by Dumas and Laurent. This led in the end to the downfall of Berzelius s dualistic theory and since the molecule as a whole was regarded as a structure which, by modification of its parts, could give rise to series of related molecules, this new point of view came to be known as the Unitary Theory. 

Gerhardt s view was confirmed by the preparation of mixed radicals , e.g. methyl + ethyl, by Wurtz by the action of sodium on mixtures of alkyl halides. All the gases, therefore, contain two radicals, the same or different. Wurtz said the protagonists of the unitary theory regarded the simple radicals as compounds of two alcohol radicals, whilst the defenders of the dualistic theory contended that they consisted of only one, Frankland gave a table of what he considered to be isomeric compounds ... 

In 1869, when Die Chemie der Jetztzeit appeared, it was the consensus among chemists that chemistry had entered a new era -- that the concepts and ideas introduced around 1860 were so far-reaching that one could talk about a wew chemistry - and many chemists looked upon August Kekule (1829-1896) as its true creator. Blomstrand, however, saw nothing new in this but had stated in the introduction to his book in bold type that the new chemistry was "only a consequential development of Berzelius atomic theory necessarily evoked by the force of many newly discovered facts" (2, p. 2). These words he thi ew into Kekul6 s camp where everyone considered Berzelius dualistic theory obsolete when in the 1830s it became evident that electronegative chlorine atoms could be substituted for... 

The acceptance of Avogadro s ideas was hindered by his rather difficult terminology. He used the terms integral molecule for the particle of a compound, constituent molecule for the particle of a gaseous element, and elementary molecule (or half molecule) for the atom of an element. Many chemists also found it hard to accept that the fundamental particles of gaseous elements contained more than one atom. An influential voice here was the Swedish chemist Jons Jacob Berzelius (1779-1848), whose dualistic theory (Chapter 7) precluded the combination of identical atoms. In consequence, Avogadro s hypothesis was poorly received by his contemporaries, and it was not given much attention by the chemical community until 1860, four years after its author had died in relative obscurity. 

Davy s move to the Royal Institution meant that he had to abandon his electrochemical researches for a while. In 1803 Berzelius and Wilhelm Hisinger (1766-1852) found that when an electric current was passed through solutions of various salts, acids were found at the positive pole and bases at the negative. This observation was probably important in leading Berzelius to the dualistic theory (see below). 

---