Before the creation of the periodic table by Mendeleev, there were several laws for the classification of the elements. One such law was Dobereiner's Law of Triads. Dobereiner between 1815 and 1829 gave his Law of Triads according to which in certain triads (groups of three elements) the atomic mass of the central element was merely the arithmetic mean of the atomic masses of the other two elements. But in certain triads all the three elements possessed nearly the same atomic masses, hence the law was rejected.
| Element 1 Atomic mass |
Element 2 Atomic mass |
Element 3 Atomic mass |
Arithmetic mean |
|---|---|---|---|
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