Why was the basis is classificatons of elements changed from the atomic mass to the atomic number ?

Explanation

1) The first attempt to classify elements was made by Dobereiner .
2 ) Dobereiner attempt gave a clue that atomic masses could be correlated with properties of elements
2 ) Newlands law of octaves also followed the same basis for classification but this law is not valid for the elements that had atomic masses higher than calcium .
4 ) Mendeleeff's classification also based on the atomic masses of elements , but it lead to some limitions like Anomalous pair elements of elements and Dissimilar elements placed together .
5 ) Moseley by analyzing the X - ray patterns of differns of differnt elements was able to calculate The number of positive charges in the atoms of respective elements .
6 ) with this analysis moseley realized that the atomic number is more fundamental characteristic of an element than its atomic weight .
7 . so he arranged the elements in the periodic table according to the increasing order of their atomic number .
8 ) This arrangement eliminated the problem of anomalous series and dissimilar . elements placed togther in Men deleeff's classification .