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Dmitri Mendeleev is often celebrated for his remarkable ability to predict the properties and even the existence of elements that had not yet been discovered. By arranging elements according to their atomic weights and properties, Mendeleev left gaps in his periodic table for elements he believed must exist. This foresight was not just guesswork; it was based on observed patterns and trends in the properties of known elements. For example, Mendeleev predicted an element similar to boron which he called "ekaboron," and accurately described its potential chemical behavior. These predictions highlighted the scientific rigor and ingenuity Mendeleev applied in developing his periodic table.

Mendeleev's predictions were rooted in his formulation of the periodic law. The periodic law states that the properties of elements are a periodic function of their atomic weights (now known as atomic numbers). This means elements exhibit recurring characteristics at regular intervals when arranged by increasing atomic weight. Mendeleev's periodic law allowed him to anticipate where gaps should exist in his table, and infer the properties of missing elements. It provided a scientific framework that transformed the understanding of chemical elements and their interactions. Thanks to this law, the layout of the periodic table became a powerful tool for ongoing scientific discovery.

The search for "ekaboron" culminated in the discovery of scandium in 1879. Mendeleev predicted this element's properties with impressive accuracy. His anticipation of scandium having an atomic weight of around 44 and behaving similarly to boron was confirmed when scandium turned out to have an atomic weight of 45. In addition, scandium's chemical properties mimicked those of boron, validating Mendeleev's forecast. The discovery of scandium became a significant endorsement of Mendeleev's predictive methodology and the utility of the periodic table as a guide in scientific exploration.

When gallium was discovered in 1875, it matched the predictions Mendeleev had made for an element he called "ekaaluminium." Mendeleev had forecast an atomic weight of 68 for ekaaluminium, which turned out to be very close to the actual atomic weight of gallium at 69.7. Moreover, gallium exhibited the low melting point and density similar to aluminum that Mendeleev had predicted. The successful prediction of gallium's properties underscored the validity of Mendeleev's periodic table and its utility in predicting not-yet-discovered elements.

Mendeleev's prediction of an element he named "ekasilicon" paved the way for the discovery of germanium in 1886. Predicted to have an atomic weight of 72, germanium was later found with an atomic weight of 72.63, and its properties aligned closely with Mendeleev's predictions. Germanium's characteristics, such as being a metalloid and forming tetravalent bonds, matched those of the supposed element ekasilicon. This discovery confirmed not only Mendeleev's predictive skills but also the robustness of the periodic table as it guided scientists in their quest to uncover unknown elements and their potential uses.