Early Attempts to Classify Elements

Law of Triads

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.

Law of Octaves

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.