Periodic Table (1869)

The Periodic Table is the most elegant organizing principle in chemistry, enabling predictions of undiscovered elements. Dmitri Mendeleev's 1869 table arranged elements by atomic weight, and his predictions of gallium, scandium, and germanium were vindicated within 15 years. It saves 50% of research time in identifying element properties compared to earlier systems, making it cheaper than the typical rival organizing system in implementation cost for chemical engineers.