Oxidation: any process by which an entity loses electrons.

e.g. 2Mgo + O2o 2Mg2+ + O2-

H2

o + F2o 2H+F-

Mg and H are oxidised in these examples.

Reduction: any process by which an entity gains electrons.

Oxygen and fluorine are reduced in the above examples.

Nomenclature: positive ions are called “ cations”negative ions are called “ anions”

Oxidation state: the sign and magnitude of the charge on an ion (also called oxidation number).

Note:1. Oxidation state of an element in the uncombined state always equal to zero.2. The algebraic sum of the oxidation states of all the atoms in the molecular formula of a compound is zero.3. In complex ions (contain more than one atom) the sum of the oxidation states of all the constituents must equal overall charge on the ion.

Common Oxidation States of Elements

1. Hydrogen usually +1.2. Oxygen usually -2.3. Halogens (i.e. F, Cl, Br, I) usually -1.4. Metal ions are invariably positive.

Example: Calculate the oxidation state of S in the S2O32- ion.

Solution: Oxidation state of oxygen is -2.

Sum of oxidation states of all the elements in the ion must equal the charge on the ion.

2 (ox. st. of S) + 3 (-2) = -22 (ox. st. of S) - 6 = -22 (ox. st. of S) = +4

oxidation state of S = +2

Example: Calculate the oxidation state of S in the S2O82- ion.

Solution: Oxidation state of oxygen is -2.

2 (ox. st. of S) + 8 (-2) = - 22 (ox. st. of S) - 16 = - 22 (ox. st. of S) = + 14

oxidation state of S = +7

Example: Calculate the oxidation state of Mn in KMnO4.

Solution: Oxidation state of oxygen is -2. 1 +ox. st. of Mn + 4 (-2) = 0

1+ ox. st. of Mn - 8 = 0ox. st. of Mn = + 7

oxidation state of Mn = +7

Nomenclature of Cations

Cation Name

Al3+ AluminiumBa2+ BariumNa+ SodiumCu+ Cuprous or copper (I)Cu2+ Cupric or copper (II)Fe2+ FerrousFe3+ FerricSn2+ StannousSn4+ StannicNH4

+ Ammonium

Nomenclature of Anions

Anion Name

Br- BromideCl- ChlorideO2- OxideS2- SulphideOH- HydroxideNO3

- NitrateCO3

2- CarbonateSO4

2- SulphatePO4

3- PhosphateCN- Cyanide

Oxidation States of Some Common Ions

Cations Anions+1 +2 +3 +4 -1 -2 -3

Li+ Be2+ Al3+ Si4+ F- O2- N3-

Na+ Mg2+ Sc3+ Mn4+ Cl- S2- P3-

K+ Ca2+ Y3+ U4+ Br- Se2-

Rb+ Sr2+ Ga3+ Th4+ I- CO32-

Cs+ Ba2+ Sb3+ Ce4+ OH- SO42-

Cu+ Mn2+ Bi3+ NO3-

Ag+ Fe2+ V3+ NO2-

Tl+ Co2+ Cr3+ CN-

H+ Ni2+ Fe3+ MnO4-

NH4+ Cu2+ Co3+

Zn2+

Cd2+

Oxidation and Reduction - Summary

Oxidation = loss of electrons

Reduction = gain of electrons

Oxidation state or number: sign and magnitude ofcharge on ion

Hydrogen +1; oxygen -2; halides usually -1; metals usually +ve.

Calculation of oxidation states in ions and molecules

Photography

light2 AgBr 2Ag + Br2

light, h