Oxidation state

As we know, an atom is stable when it has a complete octet outermost shell, i.e., the number of electrons present in the outermost shell is eight. Electrons of the outermost shell are also known as valence electrons. The oxidation state reveals the number of exchangeable electrons from the outermost shell. The oxidation state of any element can be positive or negative.

Positive oxidation state

Positive value of the oxidation state indicates the number of electrons lost by the element from its outermost shell. 

For example, the oxidation state of sodium is +1, which means a sodium atom will release one electron from its  outermost shell to form a cation. The atomic number of sodium (Na) is 11, and its electronic configuration is 1s²,2s²2p⁶,3s¹, Thus  it will readily  lose one electron from its outermost shell causing it successfully follow the octet rule and gain stability.

Negative oxidation state 

Negative value of the oxidation state indicates the number of electrons that are gained by the element . 

For example, oxidation state of the fluorine atom is -1,  the atomic number of fluorine (F) is 9 and its electronic configuration is 1s²,2s²2p⁵, so it will gain one electron from outside to complete its octet.

Oxidation process

Oxidation process of any element or compound takes place in three ways:

• Addition of oxygen atom (O) to an element or compound 
• Removal of hydrogen atom (H) from an element or a compound
• Removal of electrons from the outermost shell of the element or compound.

Reduction process

Reduction process of any element or compound takes place in three ways:

• Addition of hydrogen atom (H) to an element or compound
• Addition of electrons to an element or compound
• Removal of oxygen atom (O) from an element or compound

Examples of Oxidation reaction

From the above discussion, it is clear that in oxidation reactions, one of the reactants gets oxidised through the addition of oxygen or by the removal of hydrogen atoms or electrons.

 Few chemical reactions are discussed below:

Oxidation of alcohol

Oxidation of alcohols is carried out by oxidising agents – agents that get reduced for the oxidation of other atoms. On the basis of the kind of alcohol, oxidation yields ketone or aldehyde. Primary alcohols produce aldehydes, secondary alcohols produce ketone, and tertiary alcohols do not undergo oxidation reactions as they don’t have alpha hydrogen to remove.

The reactions can be represented as:
CH₃CH₂OH  +  Oxidising agent [O]    CH₃CHO  +  H₂O

(CH₃)₂CHOH  +  Oxidising agent [O]    (CH₃)₂CO  +  H₂O

Rusting of iron

Rust is an iron oxide compound that is formed when iron is exposed to atmospheric oxygen in the presence of moisture. Chemically, it is represented as:

Fe(s) + O₂(g) + xH₂O(l) Fe₂O₃.xH₂O(s)

Photosynthesis in plants

It is a process by which plants prepare their own food in the presence of sunlight – carbon dioxide and water molecules react to form carbohydrate and oxygen molecules as:

CO₂  +  H₂O    C₆H₁₂O₆  +  O₂

In the above reaction, carbon gets reduced and water molecules get oxidised.

Combustion reaction

Combustion reactions are those in which carbohydrates react with oxygen molecules to produce carbon dioxide gas and water molecule as:

C_xH_Y  +  O₂    CO₂  +  H₂O

In this reaction, oxygen gets reduced for the oxidation of carbohydrate molecules.

The reaction of metal with acids will produce hydrogen gas and is also an example of an oxidation reaction. In this reaction, oxidation of acid molecules takes place.

Conclusion

In this article, we have discussed the oxidation state of elements which depends on the number of exchangeable electrons from the outermost shell of that element or compound. In the oxidation process, the addition of oxygen and removal of hydrogen, as well as electrons, takes place. In the reduction process, addition of hydrogen atoms or electrons and the removal of oxidation atoms take place.