State one example of a Dobereiner’s triad’s showing in it that the atomic mass of middle element is half-way between those of the other two.

Question

State one example of a Dobereiner&#x2019;s triad&#x2019;s showing in it that the atomic mass of middle element is half-way between those of the other two.

Philoid · Accepted Answer

Acc. To Dobereiner the average of first and third element atomic masses is equal to the atomic mass of second element. For example: Lithium, Sodium and Potassium. Lithium is first element, sodium is middle element and potassium is third element so the average of atomic masses of lithium and potassium must be equal to Sodium. This is true. Atomic mass of Li is 7 while atomic mass of K is 39. And their average is 23 i.e. the atomic mass of sodium.