In 1817, Johann Döbereiner noticed a pattern when he grouped certain elements based on their atomic masses and chemical properties. He observed that elements with similar chemical properties often have atomic masses that increase in regular intervals. Döbereiner's triads consisted of groups of three elements with similar chemical properties, where the atomic mass of the middle element was approximately the average of the atomic masses of the other two elements.
In 1864, John Newlands independently proposed a similar idea called the "Law of Octaves." Newlands arranged the known elements in order of increasing atomic mass and observed that every eighth element (counting from lithium) had similar chemical properties. He likened this pattern to the repeating pattern of musical notes in an octave. However, Newlands' Law of Octaves did not work well for elements beyond calcium and was not widely accepted at the time.
By combining Döbereiner's concept of triads and Newlands' Law of Octaves, Mendeleev was able to develop the more comprehensive and accurate periodic table that we know today.
