Abstract
Ions or molecules are said to be isoelectronic if they are composed of different elements but have the same number of electrons, the same number of covalent bonds and the same structure. This criterion is unfortunately not sufficient to ensure that a chemical structure is a valid chemical compound. In a previous article, a procedure has been described to draw 2D valid structural formulas: the even-odd rule. This rule has been applied first to single-bonded molecules then to single-charged single-bonded ions. It covers hypovalent, hypervalent or classic Lewis’ octet compounds. The funding principle of the even-odd rule is that each atom of the compound possesses an outer-shell filled only with pairs of electrons. The application of this rule guarantees validity of any single-covalent-bond chemical structure. In the present paper, this even-odd rule and its electron-pair criterion are checked for coherence with an effective-valence isoelectronic rule using numerous known compounds having single-covalent-bond connections. The test addresses Lewis’ octet ions or molecules as well as hypovalent and hypervalent compounds. The article concludes that the even-odd rule and the effective-valence isoelectronicity rule are coherent for known single-covalent-bond chemical compounds.
Highlights
A chemical structural formula of a compound is a two-dimensional representation procedure initiated about two centuries ago
We already know that the group of Lewis compounds is encompassed in the group of even-odd compounds; it seems possible that another rule exits, including Lewis’ octet compounds, even-odd compounds and some more
Structural formulas of several known and unknown single-bonded compounds are drawn using the even-odd rule and the effective-valence isoelectronicity rule. They are sorted by the value of the Lewis number and the number of electrons in the outer-shell. This organization forms groups of compounds and gives an independent way to test the effectiveness of the even-odd rule with the definition of the effective-valence isoelectronicity
Summary
A chemical structural formula of a compound is a two-dimensional representation procedure initiated about two centuries ago. Avogadro [1], using the law of multiple proportions adopted by John Dalton in 1803 [2], introduced the term “molecules” to describe basic components of gases. This conception was argued with until Albert Einstein and Jean Perrin explained the Brownian movement in a liquid by the presence of molecules. Following the discovery of the electrical properties of liquids, Michael Faraday coined the term “ions” to describe compounds carrying electrical charges [5]
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