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The molecular world
The molecular world

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4 Chemical bonds consist of shared pairs of electrons

4.1 Introduction

Simple theories of chemical bonding are based on the idea of the electron-pair bond, and the extent to which the electron pair is shared between the bound atoms. There is also an assumption that the electronic structures of noble gas atoms are especially stable, and that many elements try to attain these structures when they react to form chemical compounds. These ideas were the brainchild of the American chemist, G. N. Lewis (Box 3). In developing them, we shall simplify the electronic configurations of atoms by writing shell structures that merely show the electron content of successive shells. Shell structures for atoms of elements 2-20 are shown in Figure 27.

Box 3: G.N. Lewis

Until he was 14, Gilbert Newton Lewis (1875-1946; Figure 26) was educated at home in Nebraska by his parents. It is remarkable that he did not win a Nobel Prize, because, as J. W. Linnett, sometime Professor of Physical Chemistry at Cambridge said, his idea of the electron-pair bond is 'the most productive and important contribution that has ever been made to the subject of valency and chemical binding'. In 1912, he became Chairman of a rather lacklustre chemistry department at the University of Berkeley in California. He set about reorganising and revitalising the department, appointing staff with a broad chemical knowledge rather than specalists. Under his direction, it quickly acquired the world reputation that it still enjoys today. During the First World War, he trained gas warfare specialists and was made a Lieutenant-Colonel. A love of cigars may have contributed to his death from heart failure while doing an experiment.

Figure 26
Figure 26 G.N. Lewis
Figure 27
Figure 27 A part Periodic Table showing shell structures for atoms of elements 2-20