The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called as? Give one example of such a set of elements.

AcademicChemistryNCERTClass 10

Dobereiner observed in a few atoms that the mass of one atom is equal to the average of two atoms. He defined almost all properties based on atomic weight. Hence, such an arrangement of elements called as Dobereiner triad. 

Example: Lithium has 7, sodium has 23 whereas potassium has 39 as atomic masses.
Here, we observe that the atomic mass of sodium is the average of atomic masses of potassium and lithium.
Updated on 10-Oct-2022 13:28:00