Sulekha Rani.R,PGT Chemistry ,K V NTPC Kayamkulam
Johann Wolfgang D̦bereiner (December 13, 1780 РMarch 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.
