Berzelius Dualistic Theory

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 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.)...

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. 

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). 

Berzelius explained the formation of a hydrate of copper sulphate by saying that copper sulphate was slightly positive, and this enabled it to combine with negative water. Berzelius published his first tentative account of the dualistic theory in 1812. 

The credibility of Berzelius s dualistic theory as applied to organic compounds received a further blow in 1842 when Dumas s assistant Melsens reported that trichloroacetic acid could be converted to acetic acid by the action of electrolytic hydrogen, the chlorine being simply replaced by hydrogen. Even Berzelius was now forced to admit that acetic acid and trichloroacetic acid should be formulated similarly, so he now proposed that both acids consisted of a radical combined with oxalic acid (QOj). Thus ... 

Berzelius had thus tacitly accepted the fact of substitution and had attempted to incorporate it into his dualistic theory. He applied Gerhardt s terminology to radicals such as C2H6 and QCl, calling them copulae and referring to the compounds as copulated. This new stance by Berzelius won little support, and the dualistic theory was further undermined by an accumulating mass of evidence on the composition of acids. 

Acids and bases (our acidic and basic oxides) enter as such (purement et simplement) into the composition of neutral salts without any intermediary which serves to unite them, whilst metals, on the contrary, cannot combine with acids unless they have first been more or less oxidised. It can be said rigorously that metals are not soluble in acids, but only metallic oxides , the oxygen being taken from water or from the acid, and then this oxygen must have a greater affinity for the metal than for hydrogen or the acid radical, respectively. This was the basis of the later Dualistic Theory of Berzelius (seeVol. iSo. 

It was then natural to assume further that the usual operation of elective affinity is itself electrostatic, the attraction of oppositely charged atoms of different species. Davy in England, and Jons Berzelius in Sweden, both soon came to this view, and the latter formulated an electrochemical theory of the formation of compounds, published in 1814, which put forward this dualistic hypothesis in explanation of all chemical action. Berzelius even extended these ideas into organic chemistry, proposing that groups of atoms can form compound radicals , positive and negative, which then join together as elements would. 

Two main contributors to electrochemical theory were Sir Humphrey Davy (1778-1829) in 1806 and Jons Jakob Berzelius (1779-1848) (Fig. 3.34) starting in 1811. Dualism was the basis of electrochemical theory. Oxygen, according to Lavoisier, was the central element in the system, so much so that he defined an acid as a compound of a radical with oxygen. Davy extended this concept by showing that a base was a compound of a metal with oxygen, and Berzelius (1779-1848) completed the dualistic system by assuming that, in all cases, a salt was a compound of an acid... 

Berzelius was the lirst to determine the atomic mass of the elements with satisfactory accuracy. It was he who introduced the chemical symbols still in use. His dualistic electrochemical hypothesis concerning the structure of compounds was a fundamental and progressive chemical theory for a long period. He was one of the pioneers of elemental analysis of organic substances. Berzelius wrote numerous books. His manual of chemistry has been translated into several languages and was reprinted five times in Berzelius s lifetime. In his annual reports, entitled Jahresbericht, published from 1821 until his death he critically abstracted the scientific publications of the year. The Jahresbericht was the ancestor of the numerous present scientific abstracting publications, all of them can be traced back to it. Besides cerium Berzelius discovered... 

The central theme of Berzelius s chemical doctrine was his dualistic electrochemical theory. This arose from the joint influence of Lavoisier and Davy, for both of whom he had the greatest admiration. From Lavoisier he inherited the conception of dualism ... 

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