oxidation |
reduction |
1. Addition of oxygen |
1. Removal of oxygen |
2. Removal of hydrogen |
2. Addition of hydrogen |
3. Addition of an electronegative |
3. Removal of an electronegative |
element |
element |
4. Removal of an electropositive |
4. Addition of an electropositive |
element |
element |
5. Loss of electron |
5. Gain of electron |
Oxidation number denotes the oxidation state of an element in a compound ascertained according to a set of rules formulated on the basis that electron in a covalent bond belongs entirely to more electronegative element.
Calculation of oxidation number-
1. O. S. of all the elements in their elemental form( in standard state) is taken as zero O. S. of elements in Cl2, F2, O2, P4, O3, Fe( s), H2, N2, C( graphite) is zero.
2. Common O. S. of elements of group one( 1 st) is one. Common O. S. of elements of group two( 2 nd) is two.
3. For ions composed of only one atom, the oxidation number is equal to the charge on the ion.
4. The oxidation number of oxygen in most compounds is – 2. While in peroxides( e. g., H2O2, Na2O2), each oxygen atom is assigned an oxidation number of – 1, in super oxides( e. g., KO2, RbO2) each oxygen atom is assigned an oxidation number of –( ½).
5. In oxygen difluoride( OF2) and dioxygen difluoride( O2F2), the oxygen is assigned an oxidation number of + 2 and + 1, respectively.
6. The oxidation number of hydrogen is + 1 but in metal hydride its oxidation no. is – 1. 7. In all its compounds, fluorine has an oxidation number of – 1.
8. The algebraic sum of the oxidation number of all the atoms in a compound must be zero.
9. In polyatomic ion, the algebraic sum of all the oxidation numbers of atoms of the ion must equal the charge on the ion.