Dmitri Mendeleev

Dmitri Ivanovich Mendeleev was born on 8 February 1834 in Tobolsk, Siberia, the youngest child of a huge family. His father, a school headmaster, went blind and soon died; his mother Maria kept the family alive by running its small glassworks — and when the factory burned down just as Dmitri finished school, she rode with him thousands of kilometres across the Urals to find her son a university seat. Moscow turned the Siberian boy away; Saint Petersburg’s Main Pedagogical Institute took him in; and Maria died only months later. Mendeleev never forgot what that journey had cost her.

Illness interrupted his studies and sent him south to teach in Crimea, then Odessa, before research took him to Heidelberg. From 1867 he taught at Saint Petersburg University, and in 1868 he began writing a textbook, The Principles of Chemistry, for students who had sixty-three known elements and no order among them. In February 1869, after days of shuffling the elements like playing cards, he is said to have seen in a dream a table where every element fell into its place; he woke, wrote it down, and sent it to the printers that very morning — the same day he was due to leave the city to inspect a cheese farm.

Others had noticed patterns; Mendeleev did something bolder. Where the pattern demanded an element nobody had found, he left a blank and predicted it — its mass, its density, the compounds it would form. Eka-aluminium, eka-silicon, eka-boron. When the Frenchman Lecoq de Boisbaudran discovered gallium in 1875 and reported a density of 4.7, Mendeleev wrote from Russia — never having seen a grain of the metal — that the figure should be near 5.9: measure again. The re-measurement gave 5.9. Scandium in 1879 and germanium in 1886 then walked into his empty seats like answers in a crossword. He corrected atomic weights that other chemists trusted, and when tellurium and iodine refused to obey the order of weight, he swapped them and trusted chemistry instead — a puzzle that atomic numbers would one day solve.

He died on 2 February 1907, and in his funeral procession students carried copies of the periodic table. In 1955 the scientists who created element 101 named it mendelevium — a permanent seat in the table he built. He never learned why the pattern exists — protons and electron shells were found after his death — but he trusted it anyway, and it did not fail him.