Döbereiner's Triads

Döbereiner's Triads

Before the creation of the periodic table by Mendeleev, there were several laws for the classification of the elements. One of such laws 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
Lithium 7.0
Sodium 23.0
Potassium 39.0
23.0
Calcium 40.0
Strontium 87.5
Barium 137.0
88.2
Chlorine 35.0
Bromine 80.0
Iodine 127.0
80.1
Sulfur 32.0
Selenium 79.0
Tellurium 128.0
80.0

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