Berzelius, Jons Jakob, Baron (1779-1848), the Swedish chemist who devised the system of chemical symbols and formulas. Berzelius and Wilhelm Hisinger discovered the element cerium in 1803, independently of the German chemist M. H. Klaproth, who discovered it the same year. Berzelius was the first to discover selenium (1817) and thorium (1828), and also was the first to prepare silicon (1823). Berzelius received a medical degree from the University of Uppsala in 1802. He taught medicine, pharmacology, and chemistry at the University of Stockholm (1802-15) and chemistry at the Caroline Medico-Chirurgi-cal Institution at Stockholm (1815-32). He was made a baron in 1835.

A tireless worker, Berzelius laid the foundations for modern chemistry with his experiments. He prepared a table giving the weights of 2,000 elements and compounds as compared with the atomic weight of oxygen. For his system of chemical notation he used the first letter or two of each element's name. (For instance, oxygen is O; hydrogen is H.) To indicate the number of atoms of an element in a compound, he added a figure to the symbol. Thus, the formula for water is H2O, indicating there are two atoms of hydrogen for each one of oxygen.

Berzelius experimented with electrolysis (the breakdown of chemical compounds in solution by electricity). He noted the importance of catalysis, in which a substance starts or speeds up a chemical change while undergoing no permanent change itself. He introduced the term catalyst into chemistry.