Revision notes topic questions past papers

Assigning the oxidation number

•  Oxidation number refers to a single atom or ion

•  The oxidation number of a compound is 0 and of an element (for example Br in Br

2

) is also 

0

•  The oxidation number of oxygen in a compound is always -2 (except in peroxide R-O-O-R, 

where it is -1)

•  For example in FeO, oxygen is -2 then Fe must have an oxidation number of +2 as the 

overall oxidation number for the compound must be 0

Ionic Equations

•  Ionic equations are used to show only the particles that actually take part in a reaction

•  These equations show only the ions that change their status during a chemical process, i.e: 

their bonding or physical state changes

•  The other ions present are not involved and are called spectator ions

---