Question

Dobereiner arranged elements in groups of three called ________.

Answer 1

Dobereiner arranged elements in groups of three called triads.

1. Elements with similar properties were identified and grouped together in groups of three in the increasing order of atomic masses.
2. These groups came to be known as the Dobereiner Triads after the German Chemist Johann Wolfgang Dobereiner, who came up with the law of Triads.
3. The law of triads states that the arithmetic mean of the atomic masses of the first and third elements in a triad would be approximately equal to the atomic mass of the second element in that triad.
4. The first triad were Calcium, Strontium and Barium found in the year $1817$.