Kossel–Lewis Approach to Chemical Bonding

The Kossel-Lewis approach. In 1916, Kossel and Lewis independently offered the first logical explanation for chemical bonding. Their starting observation was the chemical inertness of the noble gases -- these elements show little or no tendency to combine with other atoms. Kossel and Lewis proposed that this inertness comes from the noble gases' completely filled outer-shell (valence-shell) electronic configuration. Every OTHER element, they reasoned, tries to attain this same completely-filled configuration by losing, gaining, or sharing one or more electrons from its outer shell.

Electron transfer example (electrovalent bond). Sodium loses one electron to form the Na⁺ ion; chlorine accepts that electron to form the chloride ion Cl⁻. Both resulting ions now have the electronic configuration of their nearest noble gas ([Ne] for Na⁺, [Ar] for Cl⁻). The resulting Na⁺ and Cl⁻ ions are held together by electrostatic attractive force -- this attractive force IS the chemical bond, and because it arises from complete electron transfer it is more specifically called an electrovalent (ionic) bond.

Electron sharing (Lewis's contribution). G. N. Lewis proposed that in molecules such as diatomic nitrogen or oxygen, the same goal -- a stable electronic configuration -- is instead achieved by MUTUAL SHARING of electrons. To represent this, Lewis introduced the Lewis dot structure: the valence (outer-shell) electrons of an element are drawn as small dots placed around the element's symbol. Convention: the first four valence electrons are placed singly, one on each of the four sides of the symbol; the fifth electron onward is paired up with an existing dot. For example, nitrogen's electronic configuration is 1s² 2s² 2p³, so it has five valence electrons -- drawn as four single dots plus one pair (see Fig 10.1). Carbon (four valence electrons: 2s² 2p²) is drawn with four single dots (Fig 10.2), oxygen (six valence electrons: 2s² 2p⁴) with two single dots and two paired dots. The only exception is helium, whose valence shell holds just two electrons, represented as a single pair of dots (a duet) rather than an octet (Fig 10.3). …