Key Ideas

• Oxidants: substances that cause oxidation and are reduced themselves
• Reductants: substances that cause reduction and are oxidised themselves
• Reduction: the gain of electrons
• Oxidation: the loss of electrons

Oxidation Numbers

• The oxidation number of a free element is \(0\)
• The oxidation number of a simple ion is equal to the charge on the ion
• In compounds, some elements have oxidation numbers that are regarded as fixed, except in a few exceptions
  • Main group metals have an oxidation number equal to the charge on their ions
  • Hydrogen has an oxidation number of \(+1\) when it forms compounds with non-metals
    • In metal hydrides, the oxidation number of hydrogen is \(-1\) e.g. \(NaH\), \(CaH_2\)
  • Oxygen usually has an oxidation number of \(-2\)
    • In compounds with fluorine, oxygen will have a positive oxidation number
    • In peroxides, oxygen has an oxidation number of \(-1\) e.g. \(H_2O_2\), \(BaO_2\)
• The sum of the oxidation numbers in a neutral compound is \(0\)
• The sum of the oxidation numbers in a polyatomic ion is equal to the charge on the ion
• The most electronegative element is assigned the negative oxidation number

Writing Redox Equations