Question

Mention any two criteria for rejection of Dobereiner's triad ?​

Answer 1

Answer:

• 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.

Answer 2

The law of triads was rejected because Doberiener failed to arrange all the known elements in form of triads.Besides,The law did not fully apply within the same family.  Note_The atomic mass of the middle element of a triad was approximately equal to arithmetic mean (average)of the atomic masses of the other two elements of that triad.But,taking halogens,viz. the first three members ,Flourine (19),chlorine(35.5)and bromine(80),it is observed that the mean of the atomic masses of Flourine and bromine is 1/2(19+80)=49.5,not 35.5.  So,Dobereiner's scheme of classification of elements was not very successful,though it did contain important insights and principles.

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