Kossel – Lewis Approach to Chemical Bond Formation

Introduction

G.N Lewis was a famous American chemist that introduced the concept of LEWIS SYMBOLS to represent the valence electron in an atom. Lewis and Kossel’s theory” has studied the electronic configuration of the noble gasses and found the fact that inertness of the noble gasses is because of their complete octet or duplet in the Helium which seems to have two electrons in its last shell and offers the generalization which means” the atoms concerning the different elements seems to combine to complete their duplets or octet and avail the stable electronic configuration. In this article, we will learn about the importance of Kossel Lewis theory in chemical bond formation.

Importance Of  Lewis Symbols

The number of dots surrounding the symbol will show the number of available valence electrons, which helps calculate the standard or group valence of the particular element. According to the concept of the Kossel-Lewis approach, the atom related to different elements took active participation in combination to complete their octet (8 electrons in the outermost valence shell) or duplet ( 2 valence electrons in the outer valence shell )for attaining the nearest noble gas configuration. This complete process is known as OCTET RULE.

Ionic Bond

An ionic bond is created by the overall transference of the particular number of electrons from one atom to another atom to ensure that both of them will achieve a stable electronic configuration. The elements of groups 1 and 2 combined with halogen, sulfur, and oxygen usually create ionic bonds. There are some conditions necessary for the formation of the ionic bond and are listed below:

1. Atoms forming the (Cat) ions i.e., positive ions, need lower ionization energy, low electron affinity, low electronegativity, and high lattice energy.
2. Atoms forming (An) ions, i.e., negative ions, need to have high electron affinity, high electronegativity, high ionization energy, and lattice energy.

Some of the characteristics of the ionic bonds or electrovalent bonds are An ionic bond is formed because of the coulombic attraction among the negatively and positively charged ions. An ionic bond is non-directional, meaning that the strength of interaction among the two ions will depend on the distance factor, not the direction factor. The ionic bond is broken when the substance gets dissolved in the polar solvent or when it has been melted.

Covalent Bond

The covalent bond forms when the atoms of the same or different elements will mutually combine by sharing the electrons. Therefore, it can be said that a covalent bond is formed by the mutual sharing of the electrons, like the formation of O2 molecules.

Requirements For The Formation Of Covalent Bonds

Some of the necessary conditions for covalent bonds forms are discussed below:

• The difference in electronegativity of the non-metals should not be high
• The single bond means 2 electrons, and they follow the octet rule through electron sharing. This type of molecule seems to have a defined shape

Polar Covalent Bond

The polar covalent bond form  is defined as the bond in which the electrons are shared among the elements that have a difference of electronegativity between 0.5 and 2.0.

Dipole moment

The concept of dipole moment can be defined as the outcome of the magnitude of the charge on any of the atoms along with the distance among them. It has been represented by the Greek letter ‘µ’ and has been expressed mathematically, as:

µ = e × d

Where, e refers to charge on any one of the atoms

d determines the distance between the atoms. The unit of dipole system in the CGS system is debye (D).

Formal Charge

The formal charge is known as the hypothetical charge received from the dot structure, which means it is the electric charge difference between the valence electrons in the isolated atom and the number of electrons provided to such an atom in the LEWIS structure.

Formal Charge = [Number of valence electrons on atom] – [non-bonded electrons + number of bonds].

Postulates Of Kossel-Lewis Theory

Kossel has discussed several facts about chemical bonding, and the important postulates comprise the following:

1. The highly electronegative halogens, along with highly electropositive alkali metals, seem to be segregated by the noble gasses available under the periodic table.
2. The creation of the negative ion from halogen and positive ions from the alkali metals are related to electron gain and loss.
3. The positive ions and negative ions make the stable electronic configuration of noble gas configuration.
4. Each noble gas of the periodic table has the stable electronic configuration of the octet, excluding Helium which comprises duplet configuration.

Example: considering the formation of NaCl, NaNaCl, Na loses an electron, which is gained by chlorine. By losing an electron, NaNa will achieve the stable configuration of Neon, while ClCl, on gaining an electron will attain the stable configuration of Argon.

Na → Na⁺ + 1e^–

[Ne]3s¹

Cl + 1e^– → Cl^–

[Ne]3s²3p⁵

Importance Of Kossel Postulations

Kossel’s postulates helped in:

1. Helps in acknowledging and systemizing ionic compounds.
2. Create the foundation for latest ion-formation concepts with electron transfer

Kossel has also understood the fact that various compounds don’t fit into the concepts or categories mentioned. Lewis has provided the symbols to show the valence electron available around an atom; however, his partner Kossel introduced the postulate that explained why elements get combined with each to reach the stable electronic configuration.

Conclusion

We have explained the Lewis and Kossel theory toward chemical bonding and its importance in forming ionic and electrovalent bonds. The Lewis- Kossel approach has great significance in the formation of chemical bonds.