There was need to classify elements to systematize the study of properties of different elements and their compounds. The need gave rise to the classification properties and led to the formulation of periodic table. Dobereiner classified certain, elements into group of three, called triad. If elements of a triad were arranged in increasing order of their atomic weights, the atomic weight of the middle element was approximately the arithmetic mean of other two elements. It is referred to as law of triads. Newlands suggested that when elements are arranged in increasing order of their atomic weights, every 8th element resembles its properties, with the first one just like the 8th note of a musical scale. This is known as Newlands law of Octaves.
