Atom economy — Chemistry, 14–17
Atom economy compares how much of the starting materials becomes the useful product. It helps chemists design reactions that waste less.
What atom economy means
A reaction can make the product you want and still throw away many of the atoms you bought. Atom economy asks what percentage of the reactant atoms are found in the desired product. A high value means less built-in waste, even before the reaction is carried out.
Why chemists use it
Chemists once focused mainly on obtaining a reaction that worked. Industry then had to pay for unused atoms, separate unwanted substances and dispose of them. Atom economy gives a quick design test: can the same useful change be made with fewer atoms ending up as by-products?
Calculating it
Suppose A + B → C + D, with relative formula masses 40 + 60 → 80 + 20. If C is the desired product, add the reactant masses: 40 + 60 = 100. Divide the desired product mass by this total and multiply by 100: 80/100 × 100 = 80%. The remaining 20% belongs to D.
Atom economy is not yield
A common mistake is to call a reaction with 95% yield automatically greener than one with 70% yield. That is reasonable: yield tells you how much of the possible product you actually collected. Atom economy describes the reaction’s design, while yield describes what happened in the experiment; both matter.
Where it is used
Pharmaceutical companies use atom economy when choosing routes to make medicines. A route that uses fewer atoms in the final medicine can reduce unwanted salts, solvents and waste on a large scale. It is not the only decision: safety, cost, energy and reliability still have to be checked.
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