Introduction
The concept of electron transfer is found unable to explain the redox changes or electron shift in case of covalent compounds. To explain these changes a new concept, called oxidation number is introduced.
Oxidation number is defined as the charge that an atom of the element has in it's ion or appear to have when present in the combined state with other atoms.
Or
In other words, it is also defined as the charge that an atom appear to have in a compound when all other atoms are removed as ions from the compound.
Applications of Oxidation Number
The important applications of Oxidation no. are as follows:
(a) Stock Notation
The names of the compounds of metals showing more than one oxidation state are written by putting a Roman numeral like I, II, III.... indicating the oxidation state of the metal within the parenthesis after the symbol and name of the element. This system was introduced by Alfred Stock, a German chemist and is called the Stock Notations.
With the help of stock notations, it is possible to predict that whether the species is present in an oxidised form or reduced form.
(b) Prediction of Oxidation Reduction Reactions
In terms of the concept of oxidation number, oxidation is defined as the process in which the oxidation no. of an element increases whereas reduction is the process in which the oxidation no. of an element decreases.
Thus, it is also concluded thatthe reaction in which the oxidation states of interacting species change are called redox reactions.
(c) Prediction of Oxidising and Reducing Agents
In term of concept of oxidation number, an oxidising agent or oxidant is the substance, oxidation no. of atom of which decreases in the chemical reaction.
It is the substance that itself undergoes reduction whereas reducing agent or
reductant is the substance, oxidation no. of which increases in a chemical reaction. Thus, the substance itself undergoes oxidation.
Limitations of Concept of Oxidation Number
The limitations of concept of oxidation no. are as follows
1. Many a times the result of concept of oxidation state does not resemle with that obtained from classical approach.
2. Further it is difficult to classify some reactions as redox reaction on the basis of concept of oxidation number.
In order to overcome these limitations, the concept of redox reactions has been proposed in terms of electron density. A decrease in electron density shows the oxidation process whereas an increase in electron density around the atom(s) involved in the reaction shows a reduction process.
Comments
Post a Comment