The electronic concept explains the redox reactions in terms of transfer of electrons from one species to the other.
But the classical concept defines oxidation in terms of addition (or) removal of elements. In a chemical reaction, during the formation of products from the reactants, the loss of electrons results increase of positive charge (or) decrease of negative charge of the species.
The gain of electrons results in the decrease of positive charge (or) increase of negative charge of the species as proceed from reactants to the products in a chemical reaction.
According to electronic concept the reaction with loss of electrons, is called as oxidation and the reaction with gain of electrons is called as reduction.
And the reaction in which both oxidation and reduction takes placesimultaneously, called redox reaction.
Ex: Formation of sodium chloride from sodium and chlorine. In this reaction, sodium loses an electron and forms Na+
ion, while chlorine gains an electron and forms Cl-
Thus, according to electronic concept sodium is said to be oxidised and chlorine is said to be reduced. The part of the reaction that involves loss of electrons is called oxidation half reaction, and the part which involves gain of electrons is called reduction half reaction. The combination of both the half reactions is called as redox reaction.
In a redox reaction the substance that donates electrons to reduce the other substance is known as a reducing agent. And the substance that accepts electrons to oxidize other substance is known as an oxidizing agent.
Metals differ in their tendency to release electrons. The series obtained when the metals are arranged in the decreasing order of their ability to donate electrons is known as metal activity series or electrochemical series.