How did Dmitri Mendeleev organize elements in his first periodic table?

Dmitri Mendeleev organized the elements in his 1869 periodic table primarily by their atomic weight and their chemical and physical properties.12

Unlike his predecessors, Mendeleev placed significant emphasis on an element’s valence—the number of single bonds an element can form—to guide his arrangement. By comparing groups of elements, such as halogens and alkali metals, he discovered that atomic weights could be used to systematically arrange both the elements within a group and the groups themselves.12

His initial 1869 table featured 17 columns, or groups. Mendeleev had such confidence in his periodic law that he left gaps for elements yet to be discovered and even proposed corrections to the accepted atomic weights of several known elements. It is important to note that while he used atomic weight as a primary tool, he did not strictly adhere to ascending order if it conflicted with the observed properties of the elements.12