Question

doberneirs triads ???

Answer 1

Dobereiner arranged the elements in the group of three these were known as the triads.The law the triad states that , "When three elements are written in the order of increasing atomic masses,the atomic mass of middle element is roughly the average of the atomiser masses of other two element ."
The example is given in the pic.
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Answer 2

The first attempt towards the classification of elements was made by a German chemist Doberneir. He arranged the then known elements in the in the increasing order of their atomic masses and found that groups of 3 elements having similar properties were obtained. He called these groups of 3 elements as triads. According to him, the atomic mass of middle element of each triad was equal to the arithmetic mean of atomic masses of other two elements of that triad.
This generalisation is known as the Doberneir's law of triads.