20 August 19

Credit for the Periodic Table of Elements usually goes to Dmitri Mendeleev for the table he published in 1869. As far as we can tell he was unaware of some earlier attempts to classify the 56 elements known at that time, particularly the publication by John Newlands on 20 August 1864. Newlands' chart was based on what he called the "Law of Octaves," recognizing a pattern of similar properties for every eighth element when they were arranged in order of atomic weight. So John Newlands deserves credit for originating the "law of periodicity" so well expressed by the full Periodic Table.