Open Journal of Physical Chemistry
Vol.4 No.3(2014), Article ID:48520,8 pages DOI:10.4236/ojpc.2014.43015

Coherence of the Even-Odd Rule with an Effective-Valence Isoelectronicity Rule for Chemical Structural Formulas: Application to Known and Unknown Single-Covalent-Bonded Compounds

Geoffroy Auvert

CEA-Leti, Grenoble, France

Email: Geoffroy.auvert@grenoble-inp.org

Copyright © 2014 by author and Scientific Research Publishing Inc.

This work is licensed under the Creative Commons Attribution International License (CC BY).

http://creativecommons.org/licenses/by/4.0/

Received 5 June 2014; revised 30 June 2014; accepted 25 July 2014

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.

Keywords:Isoelectronicity, Effective Valence, Molecule, Ion, Even-Odd, Rule, Structural Formula, Covalent Bond

1. Introduction

A chemical structural formula of a compound is a two-dimensional representation procedure initiated about two centuries ago. Before 1811, atoms and molecules were thought to be similar entities. 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. Einstein used theory [3] and Perrin experiment [4] .

Following the discovery of the electrical properties of liquids, Michael Faraday coined the term “ions” to describe compounds carrying electrical charges [5] .

When comparing both, the term “isoelectronicity” [6] is used for ions and molecules having nearly the same structures. With this concept, a compound is said to be isoelectronic if it has the same number of electrons [7] [8] . Unfortunately, this property does not always give a chemically valid structure.

The recently proposed “even-odd” rule [9] [10] , introduced as a procedure to draw chemical structural formulas of ions and molecules, has not yet taken into account a possible isoelectronicity link between the represented compounds.

The aim of this paper is to check the coherence of the “even-odd” rule using compounds with a specific type of isoelectronicity named “effective-valence isoelectronicity”. Structural formulas of compounds: cations, molecules and anions, following this rule are drawn including numbers required by the even-odd rule. These numbers, associated with each element, are calculated and discussed. The state of scientific knowledge of these compounds is taken into account as well as specific isoelectronic links and resulting even-odd structures.

2. Even-Odd Rule for Ions and Molecules

The even-odd rule is a procedure to draw chemical structural formulas of molecules and ions. The structure is composed of one or several atoms of the periodic table.

As a reminder [10] , the rule is described below:

• Each atom:

¾ Is an element with one or several electron shells.

¾ Possesses an outer-shell filled with one to eight electrons.

¾ Has a number, also called valence number, of electrons in the outer-shell as indicated in the periodic table.

¾ Has a valence number of the element giving the highest number of covalent bonds that the element can form.

• A structure meets the criteria below:

¾ When it is composed of only one atom, it forms no covalent bond.

¾ When it is constituted of several atoms, each atom forms a single covalent bond with each of its first neighboring atoms. This covalent bond involves two electrons, one from each interconnected atom.

¾ A covalent bond is represented by one line between both connected atoms.

¾ An atom may have zero, one or more than one line around it.

¾ In the 2D structure, each atom is represented by the letters of its element as in the periodic table.

¾ Two numbers have to be evaluated and written on each side of the atom.

• The left side number and the effective valence number:

¾ The left side number is the valence number as in the periodic table. It ranges from one for elements like sodium (Na) up to eight for noble gas like Argon (Ar).

¾ An effective valence number has to be evaluated: For a neutral atom i.e. without charge, it is equal to the valence number; for a negatively charged atom i.e. that possesses an extra-electron, it is the valence number increased by one; for a positively charged atom, it is the valence number decreased by one.

• The right side number of an atom:

¾ The right side number, the “Lewis number”, is equal to the sum of the effective valence number and the number of covalent bonds of the atom. It can also be expressed as the sum of the number of electrons left in the outer-shell and twice the number of covalent bonds.

¾ The Lewis number must be an even number. This is only possible when the number of bonds and the effective valence number are either both odd or both even.

¾ The smallest value the Lewis number can take is zero: the atom has lost electrons from the outer-shell so it is empty and the atom has no bonds.

¾ The Lewis number can range up to twice the effective valence number: this is twice the maximum number of covalent bonds for this element. This number is charge dependent through the effective valence number.

¾ If all atoms of a compound have Lewis numbers equal to eight, the compound is compatible with Lewis’ octet rule.

• Electron pairs in the outer-shell of an interconnected atom:

¾ The number of electrons in the outer-shell is calculated by subtracting the effective valence-number and the number of covalent bonds. It is an even number.

¾ As a consequence, the outer-shell contains electron pairs not involved in any covalent bond.

¾ This electron-pair number ranges from 0 to 4 whatever the charge of the element.

¾ When this electron-pair number is 0, no additional covalent bond can be formed by the element.

The even value of the right side number i.e. the Lewis number, and the even value of the number of electrons in the outer-shell are important keys to the validity of the even-odd rule. With these even values, molecules and ions belong to a group of electron-paired compounds [9] [10] .

3. Effective-Valence Isoelectronicity Rule

An even-odd compound changes into a valid isoelectronic one when it follows the effective-valence isoelectronicity rule described below:

• The new compound configuration:

¾ Has the same covalent-bond structure.

¾ Has at least one different atom.

• The replacing atom has no impact on the outer-shell configuration:

¾ It builds the same number of single covalent-bonds.

¾ It has the same effective-valence number, as defined in the even-odd rule.

¾ It has the same Lewis number i.e. right side number.

¾ It has the same number of electrons in the outer-shell.

• But its internal configuration is different:

¾ With a different name from the periodic table.

¾ It meets one of the following criteria:

n It belongs to the same column of the periodic table (same valence number).

n It belongs to the same line of the periodic table and the valence number is corrected by a charge modification giving the same effective-valence number.

n It is shifted in column and lines of the periodic table and with a charge modification to maintain constant the effective-valence number.

From the first criteria, one example is for BH4(−) and GaH4(−). The effective-valence isoelectronicity comes from Boron and Gallium. They are in the same column of the periodic table. Only their names are different. All other parameters of the rule are the same. Since both are in the same column of the periodic table, their isoelectronicity link is obvious. Similar cases are therefore not discussed further in this article.

From the second criteria, one example is for HF and OH(−). The effective-valence isoelectronicity comes from O(−) and F. They are on the same line in the periodic table. Both have one covalent-bond, an effective valence of seven, a right side number of 8 and six electrons in the outer-shell.

From the third criteria, one example is for CH4 and PH4(+). The effective-valence isoelectronicity comes from C and P(+). They are not on the same line of the periodic table and not in the same column. Both have 4 covalent-bonds, an effective-valence number of 4, a right-side number of 8 and no electrons in the outer-shell.

References

  1. Icilio, G. (1911) Amedeo Avogadro e la sua opera scientific. Accademia delle scienze, Opere scelte di Amedeo Avogadro, Turin, i-cxl.
  2. Greenaway, F. (1966) John Dalton and the Atom. Cornell University Press, Ithaca.
  3. Einstein, A. (1905) über die von der molekularkinetischen Theorie der W?rmegeforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen. Annalen der Physik, 322, 549-560.
  4. Perrin, J. (1909) Mouvement brownien et réalité moléculaire. Annales de Chimie et de Physique, 18, 1-114.
  5. Faraday, M. (1859) Experimental Researches in Chemistry and Physics. Richard Taylor and William Francis, London.
  6. Greenwood, N.N. and Earnshaw, A. (1997) Chemistry of the Elements. 2nd Edition, Butterworth-Heinemann, Oxford.
  7. DeKock, R.L. and Gray, H.B. (1989) Chemical Structure and Bonding. University Science Books, 94.
  8. http://en.wikipedia.org/wiki/Isoelectronicity
  9. Auvert, G. (2014) Improvement of the Lewis-Abegg-Octet Rule Using an “Even-Odd” Rule in Chemical Structural Formulas: Application to Hypo and Hyper-Valences of Stable Uncharged Gaseous Single-Bonded Molecules with Main Group Elements. Open Journal of Physical Chemistry, 4, 60-66. http://dx.doi.org/10.4236/ojpc.2014.42009
  10. Auvert, G. (2014) Chemical Structural Formulas of Single-Bonded Ions Using the “Even-Odd” Rule Encompassing Lewis’s Octet Rule: Application to Position of Single-Charge and Electron-Pairs in Hypoand Hyper-Valent Ions with Main Group Elements. Open Journal of Physical Chemistry, 4, 67-72. http://dx.doi.org/10.4236/ojpc.2014.42010
  11. http://www.chemspider.com/
  12. http://www.ncbi.nlm.nih.gov/
  13. http://en.wikipedia.org/
  14. Gillespie, R.J. and Popelier, P.L.A. (2001) Chemical Bonding and Molecular Geometry. Oxford University Press, Oxford.

References

  1. Icilio, G. (1911) Amedeo Avogadro e la sua opera scientific. Accademia delle scienze, Opere scelte di Amedeo Avogadro, Turin, i-cxl.
  2. Greenaway, F. (1966) John Dalton and the Atom. Cornell University Press, Ithaca.
  3. Einstein, A. (1905) über die von der molekularkinetischen Theorie der W?rmegeforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen. Annalen der Physik, 322, 549-560.
  4. Perrin, J. (1909) Mouvement brownien et réalité moléculaire. Annales de Chimie et de Physique, 18, 1-114.
  5. Faraday, M. (1859) Experimental Researches in Chemistry and Physics. Richard Taylor and William Francis, London.
  6. Greenwood, N.N. and Earnshaw, A. (1997) Chemistry of the Elements. 2nd Edition, Butterworth-Heinemann, Oxford.
  7. DeKock, R.L. and Gray, H.B. (1989) Chemical Structure and Bonding. University Science Books, 94.
  8. http://en.wikipedia.org/wiki/Isoelectronicity
  9. Auvert, G. (2014) Improvement of the Lewis-Abegg-Octet Rule Using an “Even-Odd” Rule in Chemical Structural Formulas: Application to Hypo and Hyper-Valences of Stable Uncharged Gaseous Single-Bonded Molecules with Main Group Elements. Open Journal of Physical Chemistry, 4, 60-66. http://dx.doi.org/10.4236/ojpc.2014.42009
  10. Auvert, G. (2014) Chemical Structural Formulas of Single-Bonded Ions Using the “Even-Odd” Rule Encompassing Lewis’s Octet Rule: Application to Position of Single-Charge and Electron-Pairs in Hypoand Hyper-Valent Ions with Main Group Elements. Open Journal of Physical Chemistry, 4, 67-72. http://dx.doi.org/10.4236/ojpc.2014.42010
  11. http://www.chemspider.com/
  12. http://www.ncbi.nlm.nih.gov/
  13. http://en.wikipedia.org/
  14. Gillespie, R.J. and Popelier, P.L.A. (2001) Chemical Bonding and Molecular Geometry. Oxford University Press, Oxford.

6. Conclusions

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. As a consequence, isoelectronic single-bonded compounds form several groups completely included in the evenodd rule.

The validity of both rules is here confirmed for a large number of known compounds even if information is missing for about 15% of them. Each of these 15% is isoelectronic with known single-bonded compounds. These unavailable compounds like N(+), XeF4 or XeF3(−) may be under investigations to improve the number of known compounds and to confirm the global importance of both rules.

The next step to check the even-odd rule will probably be an adaptation to multiple-bonded compounds.

References

  1. Icilio, G. (1911) Amedeo Avogadro e la sua opera scientific. Accademia delle scienze, Opere scelte di Amedeo Avogadro, Turin, i-cxl.
  2. Greenaway, F. (1966) John Dalton and the Atom. Cornell University Press, Ithaca.
  3. Einstein, A. (1905) über die von der molekularkinetischen Theorie der W?rmegeforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen. Annalen der Physik, 322, 549-560.
  4. Perrin, J. (1909) Mouvement brownien et réalité moléculaire. Annales de Chimie et de Physique, 18, 1-114.
  5. Faraday, M. (1859) Experimental Researches in Chemistry and Physics. Richard Taylor and William Francis, London.
  6. Greenwood, N.N. and Earnshaw, A. (1997) Chemistry of the Elements. 2nd Edition, Butterworth-Heinemann, Oxford.
  7. DeKock, R.L. and Gray, H.B. (1989) Chemical Structure and Bonding. University Science Books, 94.
  8. http://en.wikipedia.org/wiki/Isoelectronicity
  9. Auvert, G. (2014) Improvement of the Lewis-Abegg-Octet Rule Using an “Even-Odd” Rule in Chemical Structural Formulas: Application to Hypo and Hyper-Valences of Stable Uncharged Gaseous Single-Bonded Molecules with Main Group Elements. Open Journal of Physical Chemistry, 4, 60-66. http://dx.doi.org/10.4236/ojpc.2014.42009
  10. Auvert, G. (2014) Chemical Structural Formulas of Single-Bonded Ions Using the “Even-Odd” Rule Encompassing Lewis’s Octet Rule: Application to Position of Single-Charge and Electron-Pairs in Hypoand Hyper-Valent Ions with Main Group Elements. Open Journal of Physical Chemistry, 4, 67-72. http://dx.doi.org/10.4236/ojpc.2014.42010
  11. http://www.chemspider.com/
  12. http://www.ncbi.nlm.nih.gov/
  13. http://en.wikipedia.org/
  14. Gillespie, R.J. and Popelier, P.L.A. (2001) Chemical Bonding and Molecular Geometry. Oxford University Press, Oxford.