In 1871, Dmitri Mendeleev, creator of the periodic table, predicted the existence of element 31 based on trends in his table. Based on its position within the table (between the known elements aluminum and indium), he named the undiscovered element eka-aluminum and correctly deduced many of its properties, including its density and low melting point—all before the physical element was actually discovered!
Gallium was discovered not long after, in 1875, by chemist Paul-Émile Lecoq de Boisbaudran. He identified the element within a sample of the zinc ore sphalerite by observing its two violet lines on a spectrometer—a device that uses light diffraction to show the unique “color fingerprint” of each element. In the same year, de Boisbaudran obtained a sample of the free metal by chemically separating it from hydroxide. His name for the element comes from the Latin word Gallia, meaning Gaul, a region that once encompassed his homeland of France.
Gallium’s discovery was a landmark confirmation that the periodic table was more than just a way to classify the elements—it was a predictive scientific model. Mendeleev’s table showed that the elemental properties followed periodic trends, even for the elements we hadn’t yet discovered.