The term atom economy is one of the fundamental and most important principles of Green Chemistry. It measures the number of atoms of reactants in a product and eventually ending up in waste. The advantage and benefit of using the atom economy are that the calculations happen early at the reaction planning stage from a balanced reaction equation. The percentage atom economy is calculated as the following: 100 times the relative molecular mass (RMM) of all atoms used to make wanted product divided by the RMM of all reactants. Traditionally, chemists are taught to maximize the yield of a reaction, however, using the principle of atom economy forces the designer to compare the different routes; choosing the most atom-efficient and avoid waste. By taking the atom economy of various synthetic routes into account at the planning stage the chosen strategy is likely to produce a greater weight of products per unit weight of reactants than might otherwise have been the case.
Sources and additional reading
Green chemistry: An Introductory Text, by Mike Lancaster, Green Chemistry Network, University of York. Published 2002