The Even-Odd Rule on Single Covalent-Bonded Structural Formulas as a Modification of Classical Structural Formulas of Multiple-Bonded Ions and Molecules

Abstract

In organic chemistry, as defined by Abegg, Kossel, Lewis and Langmuir, compounds are normally represented using structural formulas called Lewis structures. In these structures, the octet rule is used to define the number of covalent bonds that each atom forms with its neighbors and multiple bonds are frequent. Lewis' octet rule has unfortunately shown limitations very early when applied to non-organic compounds: most of them remain incompatible with the "rule of eight" and location of charges is uncertain. In an attempt to unify structural formulas of octet and non-octet molecules or single-charge ions, an even-odd rule was recently proposed, together with a procedure to locate charge precisely. This even-odd rule has introduced a charge-dependent effective-valence number calculated for each atom. With this number and the number of covalent bonds of each element, two even numbers are calculated. These numbers are both used to understand and draw structural formulas of single-covalent-bonded compounds. In the present paper, a procedure is proposed to adjust structural formulas of compounds that are commonly represented with multiple bonds. In order to keep them compatible with the even-odd rule, they will be represented using only single covalent bonds. The procedure will then describe the consequences of bond simplification on charges locations. The newly obtained representations are compared to their conventional structural formulas, i.e. single-bond representation vs. multiple-bond structures. Throughout the comparison process, charges are precisely located and assigned to specific atoms. After discussion of particular cases of compounds, the paper finally concludes that a rule limiting representations of multiple covalent bonds to single covalent bonds, seems to be suitable for numerous known compounds.

Difference in Number of Electrons in Inner Shells of Charged or Uncharged Elements in Organic and Inorganic Chemistry: Compatibility with the Even-Odd Rule

“…Since the even-odd rule limits elements to bearing a single charge or none [10], elements can only have three states: positive, neutral or negative. The state directly relates to the number of electrons of the element.…”

“…It is important here to recall that the even-odd rule also imposes that two neighbor atoms in a compound can only be interconnected by a single covalent bond [10].…”

“…Four important constrains should be remembered throughout the following: 1) Studied elements belong to the main group of the periodic table; 2) Chemical compounds are ions and molecules in gaseous or liquid phases; 3) Two neighbor elements in a compound are never connected through more than one single covalent bond [10]; 4) Elements cannot bear more than a single charge [17] [18].…”

How the Even-Odd Rule, by Defining Electrons Pairs and Charge Positions, Can Be Used as a Substitute to the Langmuir-Octet Rule in Understanding Interconnections between Atoms in Ions and Molecules

“…In previous papers, the even-odd drawing procedure has been applied to every atom of many ions or molecules [6]- [8]. In this chapter, the rule is applied to atoms in 3D molecules: two examples are displayed in Table 2 and Table 3.…”

“…In the present paper, the isoelectronicity rule is only applicable to single bonded compounds [8]. It also allows for an atom to be replaced by another only if no modifications occur in its interconnections.…”