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Drobenier's Traid

Doberiner’s Law of Triads:
According to this law, “in certain triads (grout) of three elements) the atomic mass of the central element was the arithmetic mean of the atomic masses of the other two elements.” But in some triads all the threc elements possessed nearly the same atomic masses, therefore the law was rejected.
e.g., atomic masses of Li, Na and K are respectively 7, 23 and 39, thus the mean of atomic masses of I St and 3rd element is
Limitations of Doberiner’s Triads: He could identify only a few such triads and so the law could not gain importance. In the triad ofFe, Co, Ni, all the three elements have a nearly equal atomic mass and thus does not follow the above law.
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