Dobereiner's Triads... Classification of elements

Dobereiner''s Triad- Law of Triads
Sulekha Rani.R,PGT Chemistry ,K V NTPC Kayamkulam

Johann Wolfgang Döbereiner (December 13, 1780 – March 24, 1849) was a German Chemist who is best known for work that foreshadowed the periodic law for the chemical elements.

In 1829, Dobereiner, a German scientist made

some groups of three elements each and called

them triads.

He observed that the atomic mass of the middle element of a triad was nearly equal to the arithmetic mean of

atomic masses of other two elements. All three elements of a triad were similar in their properties.

Let us take the example of three elements lithium, sodium and potassium. They form a Dobereiner’s triad.

Elements	Atomic mass
Lithium (Li)	7
Sodium (Na)	23
Potassium(K)	39

Mean of the atomic masses of the first (Li) and the third (K) elements: 7+39/ 2 = 23 u

The atomic mass of the middle element, sodium, Na =23 u

Other example..Triads.

Elements	Atomic mass
calcium(Ca)	40
barium(Ba)	88
Strontium(K)	137

Elements	Atomic mass
Chlorine	35.5
Bromine	80
Iodine	127

Mean of the atomic masses of the first and third elements =40+137/2 = 88.5 u= 88u

Mean of the first atomic masses of the and third elements =

35.5 +127/2 = 81.5 u= 80 u

Demerits:

Dobereneir’s idea of classification of elements into triads did not receive wide acceptance as he could arrange only a few elements in this manner.

Extra Information:

Döbereiner also is known for his discovery of furfural , for his work on the use of platinum as a catalyst, and for a lighter, known as Dobereiner's Lamp.