Dmitri Mendeleev Presents the First Periodic Table
He arranged 63 known elements by atomic weight and revealed a periodic pattern in their properties — famously leaving gaps that predicted elements not yet discovered.
Eka-Aluminium → Gallium
Mendeleev predicted an element with atomic weight ~68 and density ~5.9 g/cm³ that would be a soft, low-melting metal. When gallium was discovered six years later, its properties matched almost exactly — atomic weight 69.7, density 5.91 g/cm³. This was the first vindication of his periodic law.
Eka-Boron → Scandium
Mendeleev foresaw an element with atomic weight ~44 and oxide formula M₂O₃. Scandium, found in Scandinavian minerals a decade later, confirmed the prediction with an atomic weight of 44.96 — strengthening confidence in the periodic system worldwide.
Eka-Silicon → Germanium
Perhaps the most dramatic confirmation: Mendeleev predicted a grey element with atomic weight ~72, density ~5.5, and a dioxide with density ~4.7. Germanium matched on every count. Winkler himself initially thought he had found a new element unrelated to the predictions until the remarkable correspondence was pointed out.
The Gaps Fill In
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