Question

Lithium Sodium and Potassium were put in the same group based on the basis of similar properties.

If the atomic weight of Lithium and Potassium are 7 and 39 respectively what is the atomic weight of Sodium.

Answer 1

Dobereiner stated that the arithmetic mean or average of the atomic masses of the first and third elements in a triad would be approximately equal to the atomic mass of the second element in that triad.

So the atomic weight of Sodium can be calculated by taking the mean of the atomic weight of Lithium and Potassium.

The atomic weight of Sodium $=\frac{\mathrm{Lithium}+\mathrm{Potassium}}{2}$

Atomic weight of $\mathrm{Li}=7$

Atomic weight of $\mathrm{K}=39$

Therefore $\frac{7+39}{2}=23$.

Thus, The atomic weight of Sodium $\left(\mathrm{Na}\right)=23$.