Prout’s Hypothesis and Dobereiner’s Triads

Prout’s Hypothesis

                                    According to this hypothesis atomic mass of elements is multiple of mass of hydrogen atom. So elements are related to each other on the basis of their atomic masses. It fails due to the reason that some elements do not have atomic mass in whole no. (Like chlorine have atomic mass of 35.5).

Dobereiner’s Triads

                                    According to Dobereiner’s triads elements arranged in the group of three elements so that atomic mass of central element is appropriate mean of 1st and 3rd element. These groups of three elements are known as Dobereiner’s triads.
Element                                                            Li                Na                  K
Atomic Mass                                                    7                 23                  39
Mean of Atomic Masses of 1st and 3rd elements  (7+39)/2  =   46/2   =  23
Drawback of Dobereiner’s triads : All elements are not arranged in triads.
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