Question

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

Answer 1

The elements lithium, sodium and potassium form a Dobereiner’s triad. Lithium is the first element of this triad, sodium is the middle element whereas potassium is the third element of the triad. Sodium (middle element) has atomic mass 23. According to Dobereiner,

Atomic mass of Sodium = At. mass of Li + At. mass of K/2 = 7 + 39/2 = 23