Valence, elementary ideas

When, following Odling, we represent valency by dashes written after the elementary symbol, we give clear expression by means of a simple convention to certain ideas that are well understood by all among us who are versed in the fact to speak of electrons and use dots instead of dashes may serve to mislead the unwary. . . into a belief that we have arrived at an explanation of the phenomena.29... 

We now turn from the use of quantum mechanics and its description of the atom to an elementary description of molecules. Although most of the discussion of bonding in this book uses the molecular orbital approach to chemical bonding, simpler methods that provide approximate pictures of the overall shapes and polarities of molecules are also very useful. This chapter provides an overview of Lewis dot structures, valence shell electron pair repulsion (VSEPR), and related topics. The molecular orbital descriptions of some of the same molecules are presented in Chapter 5 and later chapters, but the ideas of this chapter provide a starting point for that more modem treatment. General chemistry texts include discussions of most of these topics this chapter provides a review for those who have not used them recently. 

The first main idea of this work is to refuse the assumption of possible one-step transfer of several (more than one) electrons in one elementary electrochemical act and to consider any real many-electron process as a sequence of one-electron steps. Although this idea is not new (it follows immediately from quantum theories of electron transfer [4]), it is not followed consistently in research practice. The reason is that a number of significant problems ought to be overcome in such an approach description of the accompanying intervalence chemical reactions, general scheme of the mechanism, estimation of stability of low-valence intermediate species and... 

When Berzelius theory of valence was discarded, primarily as the result of Faraday s discovery of the laws of electrolysis, the theory of acids and bases founded upon it also had to be abandoned. Doubt had already been cast on it by Davy s demonstration that hydrochloric acid did not contain oxygen. There was no doubt of the acidity of hydrochloric acid so, still thinking in terms of an elementary acidifying principle, many chemists came to regard hydrogen as the one element necessary for acid properties. Ideas regarding bases did not become so definite until the advent of the proton-donor theory. 

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