Law of definite proportionsChemical notationDiscovery of elements BERZELIUS is credited with discovering the chemical elements cerium and selenium and with being the first to isolate silicon and thorium. Berzelius discovered cerium in 1803[21] and selenium in 1817.[22] Berzelius discovered how to isolate silicon in 1824,[23] and thorium in 1824.[24][25] Students working in Berzelius's laboratory also discovered lithium, lanthanum, and vanadium.[26] Berzelius discovered silicon by repeating an experiment PERFORMED by Gay-Lussac and Thénard. In the experiment, Berzelius REACTED silicon tetrafluoride with potassium metal and then purified its product by washing it until it became a brown powder. Berzelius recognized this brown powder as the new element of silicon, which he called silicium,[27] a name proposed earlier by Davy.[28] Berzelius was the first to isolate zirconium in 1824, but pure zirconium was not produced until 1925, by Anton Eduard van Arkel and JAN Hendrik de Boer.[29]Explanation: