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The Periodic Table — CHEMISTRY STD 9 — Question

ICSE BoardEnglish MediumSTD 9CHEMISTRYThe Periodic Table2 Marks
Question
Why was Dobereiner's triad discarded?
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Answer

Döbereiner failed to arrange all the known elements in the form of triads.
In the triad of fluorine (19), chlorine (35.5) and bromine (80), it is observed that the mean of the atomic masses of fluorine and bromine is ½(19 + 80) = 49.5, not 35.5.

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