If the elements , , and form a Dobereiner's triad and the atomic weights of and are and respectively, what is the exact predicted atomic weight of the middle element ?

Question

If the elements $A$, $B$, and $C$ form a Dobereiner's triad and the atomic weights of $A$ and $C$ are $7$ and $39$ respectively, what is the exact predicted atomic weight of the middle element $B$?

Prashant Kotian · Accepted Answer

Correct answer: 23. By Dobereiner's Law of Triads, the atomic weight of the middle element is the arithmetic mean of the first and third elements. Atomic weight of . This represents the Lithium (7), Sodium (23), Potassium (39) triad.

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