|Democrite, thinker of the Vth century BC, taking back to his master Leucippe talks, suggest an atomic theory:||Matter is made from non-divisible particles ("atomos" in greek).|
|In the IVth century BC, Empedocle, contrarily to Democrite talks suggest this theory:|
Universe is made from four elements :
| At the same periode, Aristote strength the theory by adding four qualitys to the four elements: cold, dry, hot, wet. |
Those qualitys in couple form elements, who form the universe.
This theory reach to explain some freaks of nature.
Source : Cyberscol
|23 century later...|
|In 1808, John Dalton, chemist and physician, rewrite and make deeper atomic theory of democrite:|
| In 1869 Dimitri Ivanovitch Mendeleïev, chemistry professor in St-Petersburg classify elements according to their propertys. |
Writing a chemistry book, he discover that sorting elements by their atomic mass, a cyclic trend of their propertys appear several times.
First Mendeleïev table
| Mendeleïev make his table so that periodicity appear clearly, but to respect his periodicity law in which he trust, he must sometimes modify order and let some cells empty. |
He was sure that those missing elements will be finally discovered, and so predict the properys of those futur elements (according to the adjacents cells in the table): eka-aluminium, eka-bore and eka-silicium.
Between 1875 and 1886, those three elements (gallium, scandium and germanium) where discovered. Each of them had the property predicted by Mendeleïev.