Question

State Dobereiner's law of triads for the classification of elements. Support your answer by two examples.

Answer 1

According to Dobereiner's triads, the atomic mass of the middle element is equal to the arithmetic mean of the atomic masses of the other two elements of that triad.

1. Example 1 : Take three elements chlorine(35.5), bromine (80)and iodine(127).

The mean atomic mass of $\mathrm{Cl}$and $\mathrm{I}=\frac{35.5+127}{2}=\frac{162.5}{2}=81.25$,which is approximately the same as the atomic masses of bromine.

ii. Example 2 : $\mathrm{Li}\left(7\right),\mathrm{Na}\left(23\right),\mathrm{K}\left(39\right)$

The atomic mass of the middle element $\mathrm{Na}=\frac{(7+39)}{2}=23$.