Question

what were limitations of dobereiners classification

Answer 1

All the elements known at that time could not be arranged as Dobereiner's triad's example: the three elements, nitrogen, phosphorus and arsenic have similar properties. Therefore they can be regarded to form a triad. However, the actual atomic mass if the middle element, phosphorus(P)(31.0u)is much lower than the average or mean(44.45u)of the atomic masses of nitrogen and arsenic. Thus, these three elements do not constitute a Dobereiner triad in spite of their similar chemical properties.
Limitations of Dobereiner’s classification of elements: All known elements could not be classified into groups of triads on the basis of their properties. *Not all groups obeyed the Law of Triads. For example, nitrogen family does not obey the Law of Triads.
*He could only form three triad
*Due to classification into triads there was a possibility to group dissimilar elements into a single group.