Why did Dmitri Mendeleev leave gaps in his periodic table?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Periodic table of the elements with color-coded categories and labeled element groups, showing atomic numbers, symbols, and basic information for each chemical element. — periodic table Modern version of the periodic table of the elements. To learn an element's name, atomic number, electron configuration, atomic weight, and more, select one from the table.

Dmitri Mendeleev left gaps in his periodic table because he believed they represented places where as-yet undiscovered chemical elements would eventually fit.1

Mendeleev developed the periodic law by arranging elements according to their atomic weight and chemical properties, such as valence. He had such strong faith in the validity of this law that he used it to predict the existence and properties of three specific unknown elements: scandium, gallium, and germanium.213

When these elements were subsequently discovered—gallium in 1875, scandium in 1879, and germanium in 1886—their properties matched Mendeleev's predictions, which provided powerful evidence for his periodic system and led to its wide acceptance in the scientific community.23