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 )

(a) Na, Si and Cl, these three elements have different physical as well as chemical properties so they do not belong to dobereiner’s triads, even if the atomic mass of Si is equal to the arithmetic mean of atomic mass of Na and Cl.

(b) Be, Mg and Ca, these three elements have similar properties and the arithmetic mean of the atomic mass of Be and Ca is equal to the atomic mass of Mg. Therefore these elements belong to the Doberenier’s Triads.


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