Attempts were made to classify elements ever since the discovery of metals. J.W. Dobereiner in 1817 discovered that when closely related elements are grouped in a set of three, the atomic weight of the middle element was almost the arithmetical mean of the other two elements in that group.
He called such a group of three elements a triad. He could group only a few elements due to lack of knowledge of correct atomic weights of the elements at that time.
In 1863, J.A.R. Newlands, developed a system of classification of elements and entitled it as Law of Octaves. He arranged the elements is such a way that every eighth element had similar properties, like the notes of music.
The law could not apply to a large number of known elements. However, the law indicated very clearly the recurrence of similar properties among the arranged elements. Thus the periodicity was visualized for the first time in a meaningful way.