How did Mendeleev’s predictions support the periodic table?

Dmitri Mendeleev strengthened the periodic table by using his periodic law to identify inconsistencies and gaps in the existing knowledge of chemical elements.

His predictions supported the table in two primary ways:

• Correcting Atomic Weights: Mendeleev had such confidence in his system that he proposed revisions to the accepted atomic weight values for 17 known elements, asserting that the previous measurements were incorrect.12
• Predicting Unknown Elements: By identifying gaps in his table where elements with specific properties should logically exist, he predicted the existence and characteristics of three then-unknown elements: scandium, gallium, and germanium.13

The subsequent discovery of these elements—gallium in 1875, scandium in 1879, and germanium in 1886—provided empirical evidence that validated his periodic system. This success transformed the periodic table from a theoretical arrangement into a fundamental framework for chemical theory, earning Mendeleev international recognition.23