Germanium, discovered in 1886, matched Dmitri Mendeleev’s predicted element eka-silicon. Mendeleev had left a gap below silicon and estimated that the unknown element would have an atomic weight near 72 and distinctive chemical properties.
German chemist Clemens Winkler identified the new element while analyzing argyrodite, a silver sulfide mineral from Saxony. He isolated the element in 1886 and initially considered other possible identities, but its measured properties closely matched Mendeleev’s predictions for eka-silicon.
The agreement was striking: germanium’s atomic weight was measured as about 72.3, its density was close to the predicted value, and its compound germanium tetrachloride boiled below 100 °C. These confirmations helped persuade chemists that the periodic system could predict undiscovered elements.
A common mix-up is with gallium and scandium, which were also predicted by Mendeleev under the temporary names eka-aluminium and eka-boron. Germanium is the one associated specifically with eka-silicon.