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chemical bonding Introduction

Chemical Bond :

It may be defined as a force that acts between two or more atoms to hold them together as a stable molecule.

Why do atoms combine?

To answer this question we read Kossel lewis approach.

Kossel-Lewis approach to chemical bonding:

A number of attempts were made to explain the formation of chemical bonds in terms of electrons, but it was only in 1916 when Kossel & Lewis gives a satisfactory explanation. Since their theory was based on the electronic concept of atom. So it is referred to as electronic theory of valency.

Lewis postulated that atoms achieve the stable octet when they are linked by chemical bond. It can be done by two ways:-

(i) Electrovalent bond

(ii) Covalent bond

Kossel tells us the following facts:

1. The formation of a negative ion from a halogen atom and a positive ion from an alkali metal atom is associated with the gain and 1oss of an electron by the respective atoms.

2. The negative and positive ion thus formed atoms attains stable noble gas electronic configuration.

3. The negative and positive ions are stabilized by electrostatic attraction.

Application of Kossel’s postulations:

1. They provide the basis for the modern concepts regarding ion-formation by electron transfer & the formation of ionic crystalline compounds.

2. They have great value in the understanding and systematization of ionic compounds.

Octet Rule:

According to this, atoms can combine either by transfer of valence electrons from one atom to another or by sharing of valence electrons in order to have an octet in their valence shells. This is known as Octet Rule.

Lewis Symbols:

In the formation of a molecule, only the outer shell electrons take part in chemical combinations and they are known as valence electrons.G.N. lewis, introduced dot symbols for valence electrons in an atom. These notations are called Lewis dot symbols.