|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.
|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.