(1) Lithium, sodium, and potassium form Doberemer’s triad. They show similar chemical properties.
Their atomic masses are as follow:
Element |
Li |
Na |
K |
Atomic |
6.9 |
23 |
39.1 |
mass |
|
|
|
According to Dobereiner’s law or triads, the atomic mass of the middle element is approximately the arithmetic mean of the atomic masses of the other two elements.
\(\frac{6.9+39.1}{2}\) which is approximately the 23.0 atomic mass of sodium.
Thus. the atomic mass of sodium (23) is the average of the atomic masses or lithium (6.9) and potassium 39.1.
(2) Another triad of elements: Calcium (40.1), strontium (87.6) and barium (137.3).