Lone Electron Motion Delocalization and Relocalization To Write Lewis Structures Ernest C. McGoran Eastern Washington University, Cheney. WA 99004
The important thing in science is not so much to obtain new facts as to discover new ways of thinking shout them. Sir William Bragg (1) Everyone is familiar with the chemical hond and its pictorial depiction in Lewia electron dot structures (LEDS). Less clear is our image of how honds are formed; we may be inclined t o agree with Kutzelnigg (2) that "The chemical bond is a highly complex phenomenon which eludes all attempts a t simple description." Nevertheless, understanding the nature of the chemical bond and writing LEDS's are critical skills we hope to ceach our chemistry students. Expertise in the latter process often evolves only slowly because of confusion about the proper placement of valence electrons, multiple bonds, and formal charges. These features of a molecule's structure may be conjured as respectable "doodles" that prove invaluable as multiple interpretative tools, notably when combinedwith the valence shell electron repulsion (VSEPR) theory (3). As such, LEDS can furnish us with graphic pictures of molecular geometry, resonance, isomerism, hond and molecular polarities, inter- and intramolecular bonding, and the various structure/reactivity, activity, and solubility relationships. Much additional insight into chemical hond formation could be gained if the protocols for writing LEDS were to he chosen to emphasize the process over the final product. In the following we recommend a protocol for writing LEDS that evolves from agoal to meld the standard symbolisms used to depict Lewis structures with more modern interpretations given t o the covalent bond. Two recent articles in this Journal (4, 5) have eloquently argued for the importanceand ease of teaching the Ruedenberg analysis (6) of bonding theory. In this treatise we first point out that guidelines for writing LEDS can be formulated that exploit the principle of electron motion delocalization and relocalization rather than the more common closed valence shell formalism. This alternate approach profits from being intuitive and interactive. Further, i t permits the straightforward extension to writing the LEDS of hypervalent atoms and resonance structures without needing separate rules. Nature ot the Covalent BondIWrltlng LEDS Even though the covalent bond is a central premise implicit in LEDS, i t remains asubtle phenomenon that thwarts any simple portrayal. There is no one unique "valid" way to depict this abstract idea (5). Theoreticians tinker with forces, energies, wave functions or electron densities with equal justification. Any differences reflect the alternate viewpoints from which to inspect the phenomenon of bonding and the emphasis on which of these postulates is the more fundamental. A popular textbook approach for writing LEDS exploits the inert gas or closed valence shell formalism. Specialized protocols are appended for writing the LEDS of molecules havine hvoervalent atoms or resonance .. structures. The problems of constructing correct atomic frameworks from molecular formulas often adds a dimension of complexity to an already difficult task.
Despite many recent improvements in the procedures students mav use to write LEDS (7.8). most remain innately blind to
