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How did Dmitri Mendeleev arrange elements in his original periodic table?

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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 arranged the chemical elements in his 1869 periodic table primarily by increasing atomic weight.12

However, his approach was more nuanced than a simple linear sequence. Mendeleev also prioritized the chemical properties of the elements and their valence—the number of single bonds an element can form. By focusing on these properties, he intentionally deviated from a strict ascending order of atomic weight when necessary to ensure that elements with similar characteristics were grouped together.1

This methodology allowed him to identify gaps in his table, which he used to accurately predict the existence and properties of then-undiscovered elements such as scandium, gallium, and germanium. It was not until the early 20th century that scientists determined that an element's position is actually defined by its atomic number rather than its atomic weight.1