ElectrochemistryChemistry 30Unit 2

• the transfer of electrons in chemical reactions.

Reduction

•operational definition: extraction of metals from the ore

•theoretical definition: gain of electrons

Reducing agent –species that causes reduction, and is an electron donor (it is oxidized)

Oxidation

•operational definition : reaction with oxygen

•theoretical definition: loss of electrons

Oxidizing agent – is a species that causes oxidation by accepting electrons (it is reduced)

•Memory Tips:

•LEO (the lion) says GER (lose electrons and you are oxidized, gain electrons and you are reduced)

•OIL RIG (oxidation is losing electrons, reduction is gaining electrons)

Oxidation States•A method of keeping track of the electrons

that are transferred in a chemical reaction uses the oxidation states of an atom in an entity.

▫The apparent net electric charge that an atom would have if the electron pairs in a covalent bond belonged entirely to the more electronegative atom.

▫These are imaginary – they do not represent the actual charge on the atom

•The oxidation number is the positive or negative number corresponding to the oxidation state.

Common Oxidation Numbers

Oxidation Number

Exceptions

elements 0

Monatomic ions

Ion charge

hydrogen +1 -1 in metal hydrides

oxygen -2 -1 in peroxides (H2O2, K2O2, MgO2)

Rules for Assigning Oxidation Numbers

1. Assign common oxidation number

2. The oxidation numbers of compounds must add to zero

2. Molecular compounds: oxidation # assigned to more electro negative is its regular ion charge

3. Polyatomic Ions: sum of the oxidation numbers must equal the charge of the ion