Jons Berzelius (1779 - 1848)
Berzelius established that elements in inorganic compounds are joined together in definite proportions. He and his students isolated cerium, selenium, thorium, lithium, vanadium, and some of the lanthanides; they also determined the atomic weights of nearly all the elements then known. Berzelius also introduced the system of symbols still in use today, for example, H for hydrogen, O for oxygen, C for carbon, and so on.