Whose Periodic Table Organised the Elements?

Russian chemist Dmitri Ivanovich Mendeleev (1834-1907) created the most influential version of the periodic table in 1869. He arranged 63 known elements by increasing atomic weight, noticing that chemical properties repeated at regular intervals (periodicity). Crucially, Mendeleev left gaps in his table where no known element fit, boldly predicting the properties of undiscovered elements. Three of his predictions — eka-aluminium (gallium, discovered 1875), eka-boron (scandium, 1879), and eka-silicon (germanium, 1886) — were confirmed with striking accuracy, validating his system. The modern periodic table uses atomic number (protons) instead of weight, as established by Henry Moseley in 1913, but the fundamental structure remains Mendeleev.