What is Oxidation state? What are the rules for assigning Oxidation Number?

 

Oxidation Number

Any molecule, atom or Compound has residual or apparent charge (may be positive or negative) is called its Oxidation number.

• v More electronegative atom attract electron toward itself and get negative charge.
• v Less electronegative atom loss its electron and get positive charge.

       Na⁺                         Cl^-

Less Electronegative	more Electronegative
Give one electron and stable itself	Take one electron and stable itself

Rules for Assigning Oxidation Number

v Elements present in atom form having zero oxidation number e.g. Na, K, C, and Cl.

v Homonuclear molecule have zero oxidation number e.g. S₈, P₄, O₃, CL₂, H₂ etc

v Simple ions have oxidation number equal to its charge e.g. Na⁺¹ has +1 oxidation number, Cl^-1 has -1 has oxidation number and Mg⁺² has +2 oxidation number etc.

v Group 1A elements always have +1 oxidation number e.g. Na, H, K and Li have +1 oxidation number.

v Group 2A elements always have +2 oxidation numbers e.g. Ca⁺²O have +2 oxidation number.

v Oxidation number of H is generally +1 but if hydrogen combines with metals of 1A and 2A groups its oxidation state become -1 because electronegativity of hydrogen atom is always higher then metals.

v Oxidation number of oxygen in compound is -2 but most of the non-metal and compound have different combinations.