Chemical reaction may be classified according to what is happening to the reactants during the process, or the type of products formed. Oxidation state, or number, is a theoretical construct used to provide a rationale for certain chemical processes, which do not fit easily into other, more mainstream, types of reaction.
In redox reactions it is suggested that electrons are 'more attached' to electronegative atoms than to electropositive atoms. We will never know for sure whether or not this is the case, but it provides a useful model to help us explain the driving force behind one class of reactions, oxidation and reduction.
Essential idea: Redox (reduction-oxidation) reactions play a key role in many chemical and biochemical processes.
Oxidation and reduction can be considered in terms of oxygen gain/hydrogen loss, electron transfer or change in oxidation number.
An oxidizing agent is reduced and a reducing agent is oxidized.
Variable oxidation numbers exist for transition metals and for most main-group non-metals.
Applications and skills
Deduction of the oxidation states of an atom in an ion or a compound.
Deduction of the name of a transition metal compound from a given formula, applying oxidation numbers represented by Roman numerals
Identification of the species oxidized and reduced and the oxidizing and reducing agents, in redox reactions.
In Chapter 9.1