Bonds and the Structure of Molecules

Lewis dot symbols of atoms help explain the valence of elements. The orignal definition of valence was derived from the number of chemical bonds that an element would form. Counting unpaired electrons In the Lewis symbol provides the valence of elements in the s and p blocks of the periodic table. 

Because elements in the same group have the same number of valence electrons, the Lewis symbols for subsequent periods are the same, except for the identity of the elements. For example, the Lewis dot symbols for carbon, silicon, and germanium are as follows  

Of course, most molecules are more complicated than H2 or F2, and will contain more than one pair of shared electrons. If two oxygen atoms share a single pair of electrons, for example, then neither atom has an octet of valence electrons. However, if two pairs of electrons are shared, then both oxygen atoms conform to the octet rule. For diatomic nitrogen, three pairs of electrons must be shared to 

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Reprinted from The Nature of the Chemical Bond and the Structure of Molecules and Crystals An Introduction to Modem Structural Chemistry, 1st edn., by Linus Pauling, Cornell University Press, Ithaca, NY, Chapter 12, pp. 403-411 (1939). 

Pauling L (1960) The nature of the chemical bond and the structure of molecules and crystals. Cornell University Press, Ithaca... 

Pauling, L. The Nature of the Chemical Bond and the Structure of Molecules and Crystals. New York 1940. 

The result was published in 1939 as The Nature of the Chemical Bond and the Structure of Molecules and Crystals An Introduction to Modern Structural Chemistry. It would become the most important Baker lecture book ever printed, and one of the most-cited scientific texts in history. In a very basic way, this book changed the course of chemistry. For the first time, the discipline was explained not as a collection of facts tied together by practical application in the laboratory but as a field unified by an underlying physical theory Pauling s quantum-mechanical ideas about the chemical bond. By showing how the new physics explained the chemical bond, how those bonds explained the structure of molecules, and how molecules structure explained their behavior, Pauling showed for the first time, as the Nobel Prize-winner Max Perutz said, that chemistry could be understood rather than memorized. ... 

The booklet is distinguished with the simplicity of language so that no special mathematical training is required to read it. It is intended for experimental chemists, college teachers and students as well as high school students interested in the modern theory of chemical bond and the structure of molecules. 

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