Jacob Berzelius

Jacob Berzelius was one of the founders of modern chemistry. He was the first person to measure accurate atomic weights for the elements, which helped to confirm Dalton’s Atomic Theory and was the basis of Mendeleev’s periodic table. He discovered three chemical elements: cerium, thorium, and selenium, and devised the modern method by which one or two letters are used to symbolize the elements. He identified and named the phenomenon of catalysis, and described how chemical bonds can form by electrostatic attraction – nowadays called ionic bonding.

Soon after arriving to Stockholm, Berzelius wrote a chemistry textbook for his medical students, Lärboki Kemien, which was his first significant scientific publication. In 1813, he published an essay on the proportions of elements in compounds. The essay commenced with a general description, introduced his new symbolism, examined all the known elements, included a table of specific weights, and finished with a selection of compounds written in his new formalism. In 1818, he compiled a table of relative atomic weights, where oxygen was set to 100, and which included all of the elements known at the time. This work provided evidence in favour of the atomic theory proposed by John Dalton: that inorganic chemical compounds are composed of atoms combined in whole number amounts. In discovering that atomic weights are not integer multiples of the weight of hydrogen, Berzelius also disproved Prout's hypothesis that elements are built up from atoms of hydrogen. Berzelius's last revised version of his atomic weight tables was first published in a German translation of his Textbook of Chemistry in 1826.

Chemical notation

In order to aid his experiments, he developed a system of chemical notation in which the elements were given simple written labels—such as O for oxygen, or Fe for iron—with proportions noted by numbers. Berzelius thus invented the system of notation still used today, the main difference being that instead of the subscript numbers used today (e.g., H2O), Berzelius used superscripts (H2O).

Discovery of elements

Berzelius is credited with identifying the chemical elements silicon, selenium, thorium, and cerium. Students working in Berzelius's laboratory also discovered lithium, lanthanum and, vanadium. 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, a name proposed earlier by Davy.

Berzelius Measures the Weights of Atoms

Berzelius now embarked on a mammoth series of measurements and analyses of chemicals in order to discover the weights of atoms – if atoms existed. He could not measure atomic weights directly, so his idea was to use oxygen ‘atoms’ as a reference to compare the weights of other atoms with.

First he worked on gas reactions, and by 1818 had built an accurate table of atomic weights for the elements he could study as gases, vaporizing them if necessary.

He then studied reactions of oxygen with metals to deduce the metals’ atomic weights. It was easy to get these wrong, because some metal atoms combine with one oxygen atom, while others combine with two or more oxygen atoms. Utilizing a number of ingenious methods of his own and recent discoveries made by other chemists, such as Dulong and Petit’s Law, and Eilhard Mitscherlich’s discovery of isomorphism, in 1826, Berzelius published a new table of atomic weights. Even from today’s perspective, the accuracy of Berzelius’s atomic weights is impressive.

Berzelius’s atomic weights led to a much wider acceptance of Dalton’s atomic theory, and were the basis of Dmitri Mendeleev’s periodic table in 1869.