Question

Can the following groups of elements be classified as Dobereiner's triads?

(a) Na, Si, Cl
(b) Be, Mg, Ca
Give reason for your answer.
(Atomic masses : Be 9 ; Na 23 ; Mg 24 ; Si 28 ; Cl 35.5 ; Ca 40)

Answer 1

Can the following groups of elements be classified as Dobereiner's triad? ... (a) No, because all these elements do not have similar properties although the atomic mass of silicon is average of atomic masses of sodium (Na) and chlorine (Cl).

Answer 2

The atomic mass of Na is 23 and Si is 28 whereas Cl is 35.5.

As per Dobereiner’s triads, the elements that are arranged in the ascending order are totally based on the atomic masses; you can get a three element group that holds the same chemical properties.

The atomic number of the middle element is equal to the arithmetic mean of atomic masses of the other two atomic elements.