Question

What are Döbereiner triads?

Answer 1

In the history of the periodic table, Döbereiner's triads were an early attempt at organizing the chemical elements by certain physical properties. In 1829, the German chemist Johann Wolfgang Döbereiner pointed out that there were triads of elements that showed similar chemical properties. He also noticed the fact that the atomic weight of the central element of the triad is approximately the mean of the atomic weights of the other two members. The properties of the middle element were in between those of the end members.