Lithium, sodium and potassium form a Dobereiner’s triad. The atomic masses of lithium and potassium are 7 and 39 respectively. Predict the atomic mass of sodium.

Question

Lithium, sodium and potassium form a Dobereiner’s triad The
atomic masses of lithium and potassium are 7 and 39 respectively
Predict the atomic mass of sodium

Sushree Simran · Accepted Answer

Let us take example of three elements (triads): Lithium, Sodium and
Pottasium

Atomic mass of lithium = 7
Atomic mass of Potassium = 39

Sum of the atomic masses of lithium and potassium = 7 + 39 = 46
Average of their atomic masses =

Therefore, the atomic mass of sodium = average of the atomic mass
of lithium and potassium = 23