Introduction

This unit opens with a line from the Greek philosopher Democritus -- "we think there is colour, we think there is sweet, we think there is bitter, but in reality there are atoms and a void" -- setting up the idea that the enormous variety we perceive around us is built from a small number of fundamental building blocks combining in different ways.

What this unit sets out to do. By the end of it you should be able to:

• classify any substance around you as an element, a compound or a mixture;
• define atomic mass and molecular mass, and understand why chemists use a relative mass scale rather than weighing atoms directly;
• define the mole as chemistry's counting unit (the SI unit for "amount of substance"), and use Avogadro's number to move between number of atoms/molecules, mass and moles;
• define equivalent mass, and calculate the equivalent mass of an acid, a base, or an oxidising/reducing agent;
• work out a compound's empirical and molecular formula from experimental composition data;
• solve stoichiometric problems using a balanced equation, and identify the limiting reagent in a reaction run with non-stoichiometric amounts;
• define oxidation, reduction, oxidant and reductant; assign oxidation states; classify redox reactions into types; and balance a redox equation from its two half-reactions.