The "6N+2 Rule" for writing Lewis octet structures

chemicd principle1 revi~i ted

Edited by DAN KALLUS Midland Senior High School 906 W. illinais Midland, TX 79705

The "6N+2 Rule" for Writing Lewis Octet Structures Melvin E. Zandler and Erach R. Talaty Wichita State University, Wichita, KS 67208

Lewis octet structures (LOSS) constitute an overwhelming majority of the structures that students encounter in a course in general chemistry, organic chemistry, or biochemistry. Hence, the writing of LOSS corresponding to a given molecular formula is an important exercise for them. The ability of students to write these structures correctly, and then to calculnte the formal charges of thr atoms in\,ol\,ed,is a prerequisice to understanding such topics as acidity and basicity, resonance, molecular geometry, structural isomerism, and reactivity. Thus, if Lewis structures are written for all of the oxyacids of chlorine, their observed increase in acidity as more oxygen atoms are attached to the chlorine atom can be rationalized by an increase in formal charge of the central atom in passing from HClO to HC102 to HC103 to HC104. Determination of the structure of an organic compound from elemental analysis and spectral data requires the ability to choose among a set of isomeric Lewis structures. Despite the unquestionable necessity of learning how to write Lewis structures, many textbooks do not give any procedures for writing such structures. Some textbooks do provide equations or rules, but they appear to be unnecessarily complicated and too difficult to be remembered (1-5). An earlier article in THIS JOURNAL gave rules that are useful for writing resonance structures (6).

This rule leads to quickly recognized "magic" numbers of valence electrons (8, 14, 20, 26, 32, 38, etc.) for compounds devoid of multiple bonds or rings. Now, an extra bond can only be introduced into any allsingle-bonded, noncyclic Lewis octet structure that is shown in Figure 1,without violation of the Octet Rule, at the expense

The "6N+2 Rule"

We recommend a set of instructions for writing LOSSwhich incorporates as a central feature the applicatiun ot a sirnplt, rule, which we call the "GN-'2 I