1.1 Formulae and equations

Oxidation number is the number of electrons that need to be added to or taken away from an element to make it neutral.

• The oxidation number of an uncombined element is 0.
• The sum of the oxidaton number in a compound is 0.
• The sum of the oxidation number in an ion equals the overall charge.
• In compounds the oxidation numbers of Group 1 metals is +1 and Group 2 metals is +2.
• The oxidation number of oxygen is -2 in compounds (except with fluorine or in peroxides or superoxides)
• The oxidation number of hydrogen is +1 in compounds (except in metal hydrides)
• In chemical species with atoms of more than one element, the most electronegative element is given the negative oxidation number.

• Write a word equation for the reaction
• Write the symbols/formulae for each reactant and product
• Balance the equation by multiplying the formulae
• Check your answer
• Add state symbols