Reduction–Oxidation (REDOX) Reactions

In a chemical reaction electrons are lost or gained or shared.

When an element loses an electron or electrons the element is said to have been oxidised. The element thereby becomes positively charged.

element - e- → element +

When an element gains an electron or electrons the element is said to have been reduced. The element thereby becomes negatively charged.

element + e- → element -

Reduction = Gain of electrons (RedGain) Oxidation = Loss of electrons (OxiLoss)

Standard/ Class/ Grade XI ChemistryChapter 5 Redox Reactions

Gurudatta K Wagh, gkwagh@gmail.com

To understand the reduction-oxidation reaction let us take one example. Magnesium and oxygen react to form magnesium oxide. The balanced chemical equation of the reaction is2Mg + O2 → 2MgO

How does the reaction proceed? We have to look at the electronic configurations of both the reactants.

Magnesium has the electronic configuration 1s22s22p63s2

The third shell of magnesium contains 2 electrons. It requires six more electrons to complete the octet. It is easier for magnesium to become stable by losing the two electrons in the third shell. Magnesium thus becomes stable since the second shell contains eight electrons and the octet of electrons is completed. Thus we see

2Mg → 2Mg2+ + 4e-

The electronic configuration of oxygen is 1s22s22p4

Oxygen requires two electrons in its second shell to complete the octet and become stable. It is easier for oxygen to accept two electrons and achieve stability. Oxygen accepts the electrons released by magnesium. We get

O2 + 4e- → 2O2-

The net reaction can be written as

2Mg + O2 + 4e- → 2Mg2+ + 4e- + 2O2-

Cancelling the 4e- on both the sides the reaction can be written as

2Mg + O2 → 2Mg2+ + 2O2- → 2MgO

The loss of electrons by magnesium is called oxidation of magnesium. The gain of electrons by oxygen is called as reduction of oxygen.