How did Dmitri Mendeleev revise his periodic table in 1871?

In 1871, the Russian chemist Dmitri Mendeleev significantly revised his original 1869 periodic table by restructuring it from 17 columns into an eight-group format.1

This revision was part of his broader effort to refine the periodic law, which organized elements based on their atomic weight and chemical properties. Key aspects of his 1871 update included:12

• Correction of Atomic Weights: Mendeleev correctly identified that the then-accepted atomic weights for 17 elements were inaccurate.1
• Predictive Power: By identifying gaps in his table, he successfully predicted the existence and specific properties of three then-unknown elements: scandium, gallium, and germanium.13

These improvements helped solidify the periodic table as a foundational framework for chemical theory, gaining widespread scientific acceptance following the subsequent discovery of the elements he had predicted.12