In order to help students draw Lewis structures correctly and easily, various approaches have appeared in the research literature and general chemistry textbooks. Lever proposed "6N+2" rule for noncyclic molecules, in which the number of π bonds can be determined by the total number of valence electrons and the total number of atoms in a molecule. Following this proposed rule, Clark provided detailed procedures for writing Lewis octet structures without understanding σ or π bonding. In the same year, Zandler & Talaty 2 listed more examples to account for more types of species, such as cyclic molecules. However, the rule is not applicable to non-octet Lewis structure or odd-electron structure.