Question

Li, Na, Pt form a dobereiner’s triad. The atomic masses of Li and Pt
are

7 and 39. respectively. Predict the atomic mass of Na?​

Answer 1

Answer:

Atomic mass of Na is 23.

Explanation:

According to dobereiner's triad rule, the atomic mass of middle element is arithmetic mean of first and last element.

Here, Atomic mass of Na= (Atomic mass of Li+Pt)/2

That is Atoomic mass of Na=(7+39)/2 =23

Answer 2

Solution:

As per the Doberiener's law,

When elements are arranged in increasing orders of their atomic masses, the arithmetic mean of the atomic masses of the first and the third element in a triad is approximately equal to the atomic mass of the second element in that triad.

Therefore, Mean of atomic masses of Li and atomic masses of Potassium= atomic mass of Sodium

7+39/2

=46/2

=23

=Atomic Mass of Sodium