Oxidation, Reduction and Redox Equations
Oxidation is loss, reduction is gain (of electrons)
OIL RIG
Reduction and oxidation occur simultaneously
Oxidising agent – electron acceptor
Reducing agent – electron donor
Oxidation state – Hypothetical charge on an atom in a compound or an ion when that species,
regardless of the nature of bonding, is regarded as totally ionic
Oxidation State Rules
Uncombined elements have an oxidation state of 0, and elements just bonded to identical
atoms also have an oxidation state of 0
o E.g. Mg (0), H2 (0)
Oxidation state of a simple monoatomic ion is the same as its charge
o E.g. Na+ (+1), S2- (-2)
Sum of all oxidation states in a compound is equal to 0
o E.g. MgCl2 (+2, -1, -1)
Some metal elements have fixed oxidation states in compounds
o Group 1 metals - +1 in compounds
o Group 2 metals - +2 in compounds
o Group 3 metals - +3 in compounds
Hydrogen is +1 in compounds, except in metal hydrides where it is -1
o E.g. H2O (+1, +1, -2), NaH (+1, -1)
Oxygen is always -2, except in peroxides where it is -1
o E.g. CO2 (+4, -2, -2), H2O2 (+1, +1, -1, -1)
Fluorine is always -1 as it is the most electronegative element
o E.g. HF (+1, -1)
Halogens are also -1 except where the other element is more electronegative
o E.g. LiI (+1, -1), ICl (+1, -1)
The sum of the oxidation numbers of the atoms making up a molecular ion equals the charge on
the molecular ion
o E.g. SO42- (+6, -2, -2, -2, -2 = -2)
Showing Oxidation States
Sometimes, oxidation states aren’t clear from the formula of a compound
Roman numerals are used in a chemical name to indicate the oxidation number
E.g. Copper (II) sulphate – Cu +2
Half-Equations
Overall equation for a redox reaction can be separated into two half equations – one shows
reduction and one shows oxidation
Oxidation is loss, reduction is gain (of electrons)
OIL RIG
Reduction and oxidation occur simultaneously
Oxidising agent – electron acceptor
Reducing agent – electron donor
Oxidation state – Hypothetical charge on an atom in a compound or an ion when that species,
regardless of the nature of bonding, is regarded as totally ionic
Oxidation State Rules
Uncombined elements have an oxidation state of 0, and elements just bonded to identical
atoms also have an oxidation state of 0
o E.g. Mg (0), H2 (0)
Oxidation state of a simple monoatomic ion is the same as its charge
o E.g. Na+ (+1), S2- (-2)
Sum of all oxidation states in a compound is equal to 0
o E.g. MgCl2 (+2, -1, -1)
Some metal elements have fixed oxidation states in compounds
o Group 1 metals - +1 in compounds
o Group 2 metals - +2 in compounds
o Group 3 metals - +3 in compounds
Hydrogen is +1 in compounds, except in metal hydrides where it is -1
o E.g. H2O (+1, +1, -2), NaH (+1, -1)
Oxygen is always -2, except in peroxides where it is -1
o E.g. CO2 (+4, -2, -2), H2O2 (+1, +1, -1, -1)
Fluorine is always -1 as it is the most electronegative element
o E.g. HF (+1, -1)
Halogens are also -1 except where the other element is more electronegative
o E.g. LiI (+1, -1), ICl (+1, -1)
The sum of the oxidation numbers of the atoms making up a molecular ion equals the charge on
the molecular ion
o E.g. SO42- (+6, -2, -2, -2, -2 = -2)
Showing Oxidation States
Sometimes, oxidation states aren’t clear from the formula of a compound
Roman numerals are used in a chemical name to indicate the oxidation number
E.g. Copper (II) sulphate – Cu +2
Half-Equations
Overall equation for a redox reaction can be separated into two half equations – one shows
reduction and one shows oxidation
