Lewis cubical bonding model

Fig. 1 Lewis cubical atom model of a double bond (left) and placement of the electron pairs on edges of the cube to account for the tetrahedral arrangement of the four bonds of an atom (right)...

Whenever Lewis appfied his model to covalent compounds, he noted that the atoms seemed to share pairs of electrons. He also noted that most compotmds contained even numbers of electrons, which suggested that electrons exist in pairs. He therefore replaced his cubic model of the atom, in which eight electrons were oriented toward the surfaces of a cube, with a model based on pairs of electrons. In this notation, each atom is surrounded by up to fotu" pairs of dots, corresponding to the eight possible valence electrons. This symbohsm is still in use today. The only significant modification is the use of fines to indicate covalent bonds formed by the sharing of a pair of electrons. The Lewis structures for F2 and O2 are written as follows ... 

Lewis s interest in chemical bonding and structure dated from 1902. In attempting to explain "valence" to a class at Harvard, he devised an atomic model to rationalize the octet rule. His model was deficient in many respects for one thing, Lewis visualized cubic atoms with electrons located at the corners. Perhaps this explains why his ideas of atomic structure were not published until 1916. In that year, Lewis conceived of the... 

Lewis s model established the idea of the nonpolar covalent bond, although his idea of the cubic arrangement of electrons had several major flaws, for example, how to represent a triple bond in which six elec-... 

In 1902, while explaining the laws of valence to his students at Harvard, Lewis conceived a concrete model for this process, something Abegg had not done. He proposed that atoms were composed of a concentric series of cubes with electrons at each of the resulting eight comers. This cubic atom explained the cycle of eight elements in the Periodic Table and corresponded to the idea that chemical bonds were formed by the transfer of electrons so each atom had a complete set of eight electrons. Lewis did not publish his theory, but fourteen years later it became an important part of his theory on the shared electron-pair bond. 

Lewis s cubical atom [3-72] deserves special mention. It was instrumental in shaping the concept of the shared electron pair. It also permitted a resolution of the apparent contradiction between the two distinctly different bonding types, viz., the shared electron pair and the ionic electron-transfer bond. In terms of Lewis s theory, the two bonding types could be looked at as mere limiting cases. Lewis s cubical atoms are illustrated in Figure 3-51. They are also noteworthy as an example of a certainly useful though not necessarily correct application of a polyhedral model. 

What is curious about this article of 1916 is that Lewis begins with a detailed account of his cubic atom but in the very same article shows that it is necessary to go beyond this model. One of the shortcomings of the simple model is its inability to explain the formation of triple bonds such as in a molecule of ethyne (acety-... 

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