In 1817, Johann Wolfgang Dobereiner thought that he had made a great observation about elements. He thought that there was a relationship between the atomic weights of elements and their properties. His theory was that, in groups of three (triads), the middle element had the mean atomic mass of the two elements to either side of it. This works with many elements, like Lithium, Sodium and Potassium. (Li + K) / 2 = Na (7 + 39) / 2 = 23 (1 jan 1817 ano – 23 h 59 m, 31 dez 1817 ano)
Adicionado na linha do tempo:
Data:
1 jan 1817 ano
23 h 59 m, 31 dez 1817 ano
~ 12 months