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 .