What r limitations of dobreiner law of classification?

1.	What r limitations of dobreiner law of classification?
Answer» Limitations of Dobereiner\'s classification: Dobereiner could find only three triads; .i.e total of 9 elements only. However the total number of elements were more than that of those encompassed in Dobereiner\'s Triad. Thus,Dobereiner\'s could not be classify most of the elements known at that time.This was a major drawback of Doberenier’s triads.He stated that when three elements of same chemical properties were arranged in order of their increasing atomic masses, the sum of first and third element was rougly the average of the middle element. But, three elements nitrogen, phosphorus and arsenic have same chemical properties, but these three elements do not follow Doberenier’s rule.Atomic mass of nitrogen is 14 u and that of arsenic is 74.9 u but their average is 14+74.9/2= 44.45 u which is much higher than atomic mass of phosphorus i.e, 31 u.

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