Swedish chemist who was a disciple of Dalton. He developed the concepts of the ion and ionic compounds. This theory made the idea of the O₂ molecule ridiculous, and helped bring about the rejection of Avogadro's Hypothesis. Berzelius embarked on a systematic program to try to make accurate and precise quantitative measurements and insure the purity of chemicals. After Lavoisier, Berzelius is known as the father of chemistry. He determined the exact elementary constituents of large numbers of compounds. The results strongly confirmed Proust's Law of Definite Proportions. He published a table of atomic weights in 1826 which was in good agreement with modern values (although some weights are off by a factor of 2 or 1/2), but included confusion as to the differences between atoms and molecules. In his weights, he used oxygen as a standard, setting its weight equal to exactly 100. He also measured the weights of 43 elements. He found that the weights of compounds were not integer multiples of the hydrogen atom.

Motivated by his extensive atomic weight determinations, he introduced the classical system of chemical symbols in 1811, in which elements are abbreviated by one or two letters to make a distinct abbreviation from their Latin name. Berzelius developed the radical theory of chemical combination, which holds that reactions occur as stable groups of atoms called radicals are exchanged between molecules. He believed that salts are compounds of an acid and bases, and discovered that the anions in acids would be attracted to a positive electrode, whereas the cations in a base would be attracted to a negative electrode. Berzelius did not believe in the Vitalism Theory, but instead in a regulative force which produced organization of tissues in an organism.

Avogadro, Dalton, Lavoisier, Proust