An arrangement in which the properties of specific elements reappear again an again at a regular interval is called periodic classification.
Many attempts were made to classify the known element from time to time.
The earlier attempts are as follows :
Prout's Hypothesis : According to this theory, hydrogen atom was considered as the fundamental unit and atomic weights of all elements were considered as multiple of hydrogen's weight.
Dobereiner's Triads : Dobereiner classified the elements into groups of three elements with similar properties in such a manner, so that the atomic weight of the middle element was the arithmetic mean of the other two,
Newland's Law of Octaves : Newland's states that when elements are arranged in order of increasing atomic masses, every eighth element has properties similar to the first, just like in the musical note.
