Question

What was Johann Dobereiner’s contribution to the development of the periodic table?
He arranged the elements according to increasing atomic mass.
He arranged the elements according to increasing atomic number.
He identified triads of elements that had similar properties.
He organized elements into four groups based on their properties.

Answer 1

He identified triads of elements that had similar properties. Dobereiner noticed groups of three elements (e.g., Li–Na–K, Ca–Sr–Ba, Cl–Br–I) whose properties were similar and whose middle element’s atomic mass was approximately the average of the other two.