Question

short notes on doberiners triads.

Answer 1

In 1817, Johann Wolfgang Dobereiner, a German chemist, classified elements into groups based on their properties. He kept all elements having similar properties in one group. Most of his groups had three elements each. Thus, he called these groups as triads. He also gave a law known as the Law of Triads. It states that when three elements in a triad are listed in the increasing order of their atomic masses, the atomic mass of the middle element will roughly be the average of the atomic masses of the other two elements. For example, lithium, sodium and potassium form a triad. When the average of atomic masses of the first and the last elements are taken, then it comes out to be equal to the atomic mass of the second element that is sodium. 

Atomic mass of lithium = 7

Atomic mass of potassium = 39

Average atomic mass of lithium and potassium = (7 + 39) / 2 = 23

Atomic mass of sodium = 23

Answer 2

In the history of the periodic table, Döbereiner's triads were an early attempt to sort the elements into some logical order by their physical properties. In 1817, a letter reported Johann Wolfgang Döbereiner's observations of the alkaline earths; namely, that strontium had properties that were intermediate to those of calcium and barium.[1] By 1829, Döbereiner had found other groups of three elements (hence "triads") whose physical properties were similarly related.[2] He also noted that some quantifiable properties of elements (e.g. atomic weight and density) in a triad followed a trend whereby the value of the middle element in the triad would be exactly or nearly predicted by taking the arithmetic mean of values for that property of the other two elements.