OXIDATION NUMBER

OXIDATION NUMBER

Oxidation number is the number of charge on a charged element Ca2+,Na+ (usually called ion) or a group of charged elements called radical e.g. SO42- , NO3-   e.t.c.

The oxidation number can be calculated by following simple rules.

1. The number of charge on the radical is the overall charge of the ion. Hence we can say Ca2+ has a charge of +2, while Na+ is +1, while SO42- , has a charge of -2.

2. When an atom or group of atoms has no charge, it has an overall charge of zero.

NOTE: Unless otherwise stated, the oxidation number of oxygen is -2. While most group 1,2, and 3 metals like Na, K, and Ca usually retain their natural value based on their group. 

Some with multiple oxidation numbers have their charges written in Roman numerals after their names.

CO2 - Carbon (IV)oxide

H2SO4- Hydrogentetraoxosulphate(IV)

NaNO3- Sodium trioxonitrate(V)

When the element is positively charged, the suffix is pronounce - ate at the end of the  e.g. carbonate, sulphate however when the element is negatively charged it is pronounce as an  -ide charge.

EXAMPLES OF OXIDATION NUMBER CALCULATION.

Calculate the oxidation of

1. Carbon in CO2

Since there is no charge on the compound, the overall charge is zero. While the oxidation number of oxygen is -2.

Hence we have that 

C + (2 x -2)=0

C + ( -4) =0

C = +4. The name of the compound is carbon(IV)oxide

2. Chromium in K2Cr2O7

Since there is no charge on the compound, the overall charge is zero. While the oxidation number of oxygen is -2, the charge on potassium K is +1.Also bear in mind the we have 2 atoms of Cr

Hence we have that 

2Cr +(2 x+1) + (7 x -2)=0

2Cr +2+(-14)=0

2Cr -12=0

2Cr = +12

Cr = +12/2

Cr = +6. The name of the compound is heptaoxodichromate(VI)

3. Manganese in MnO4- 

In this here is an overall charge of -1 on the compound while the oxidation number of oxygen is -2.

Mn +(4 x -2)=-1

Mn +(-8) =-1

Mn = +8 -1

Mn = +7. The name of the compound is tetraoxomanganate(VII)