Dmitri Mendeleev

Periodic table

Mendeleev’s periodic table is a classification tool, not a physical device. It organises known elements by atomic weight and valence to expose recurring chemical patterns. It correctly predicted properties of undiscovered elements — gallium, scandium, germanium — and corrected atomic weights and valences of known ones, like uranium. Its mechanism is interpolation across ordered rows and columns. It fails where atomic weight order conflicts with chemical behaviour — a flaw later resolved by atomic number. It changed chemistry from descriptive cataloguing to predictive science. It is worth your time because it demonstrates how a simple ordering principle, rigorously applied, becomes a discovery engine.