Question

Which will be the third element among the given elements to complete the given Doberiener triad?

(Atomic mass of $\text{Be= 9, Na= 23, Mg= 24, Si= 28, Cl= 35, Ca= 40}$)

$\text{Na, \_\_ , Cl}$

Answer 1

Because all these elements do not have similar properties although the atomic mass of silicon is almost the average of atomic masses of sodium ($Na$) and chlorine ($Cl$).

That is $35+23=58;58/2=29$ approximately equal to $28$ which is the atomic weight of silicon. Only these three elements can be done in this form.

Hence, the third element in the triad is Silicon ($\text{Si}$).