The Russian chemist who, in 1869, arranged the sixty-odd known elements by atomic weight into a single table whose recurring pattern he called the periodic law — and who set himself apart from others circling the same idea by leaving gaps for undiscovered elements and predicting their properties in detail. When gallium, scandium, and germanium were found within fifteen years, matching his forecasts with startling precision, the periodic table became the organizing map of chemistry. He worked without knowing why the pattern held; the deeper basis, atomic number, came only later through Moseley. Element 101, mendelevium, bears his name, though he never won the Nobel Prize.
In 1871 a Russian chemist did something almost no one dares. He pointed at the blank squares in his new table of the elements and told the world exactly what would fill them. One missing element, he said, would be a soft gray metal of a certain weight and density; he called it eka-aluminium. Four years later a Frenchman isolated a new metal, gallium — soft enough to melt in a warm hand — and its properties matched the forecast almost line for line. Two more predicted elements, scandium and germanium, followed and fit just as well. Dmitri Mendeleev had not merely sorted the known elements. He had drawn a map with holes in it and named what the holes would hold.