Earlier Attempts to Classify Elements

Long back elements were classified as metals and non-metal. Following the development of atomic theory, attempts were made to classify elements.

Dobereiner classified certain elements into groups of three, called Triads. In a triad elements were such that the atomic mass of middle element was average atomic mass of 1^st & 3^rd elements 

	1st	2nd	3rd
Triad	Li	Na	K
Atomic Mass	7	23	39

Atomic Mass of Na = (39 + 7) / 2 = 46 / 2 = 23

However, only limited elements could give such triads. Newland observed that if elements are arranged in order of their atomic weights, the eighth element starting from a given one is kind of repetition of the first (like eighth note of Music) Newland called it the Law of Octaves.

Lothar Meyer plotted a graph of atomic volume versus atomic weights of different elements. He observed similar elements were found to occupy similar positions on his curve.