1813

Chemical Notation

John Dalton (1766–1844), Jöns Jacob Berzelius (1779–1848)

Swedish chemist Jöns Jacob Berzelius began his career as a physician in 1802, but his impact on the field of chemistry is hard to overstate. By 1818, he was a professor at the prestigious Karolinska Institutet (which now awards the annual Nobel Prize in Physiology or Medicine), permanent secretary of the Royal Swedish Academy of Sciences, and the author of a highly influential chemistry textbook. He discovered the elements silicon, selenium, thorium, and cerium, and he was apparently the first chemist to realize that the entire field could be divided into the chemistry of carbon compounds (organic chemistry) and everything else (inorganic chemistry). He also coined words like protein, polymer, isomer, and allotrope, which can be found throughout this book.

Additionally, Berzelius helped to codify atomic and molecular weights. The former, he found, were not simply multiples of hydrogen, but the latter did seem to be combinations of whole-number ratios of the various elements, which was a big piece of evidence in favor of John Dalton’s atomic theory, the cutting edge of chemical thought at the time. In 1813, this led Berzelius to start writing chemical formulas down in an element-plus-number style to keep track of them. He gave the elements simple one- or two-letter abbreviations and then wrote next to each element the number of that element a given compound seemed to be carrying, using superscripts rather than the subscripts we are familiar with today. Hence, table salt (sodium chloride) was written as NaCl, and baking soda (sodium bicarbonate) was identified as NaHCO³. That is, each molecule of salt consists of one sodium and one chlorine, and each molecule of baking soda consists of one sodium, one hydrogen, one carbon, and three oxygens. The fact that there was another well-known molecule, now known as sodium carbonate (with the formula Na₂CO₃), immediately suggested something about the structures as well: CO₃ is one unit, and sodium, potassium, hydrogen, and other elements can be swapped in and out around it. Chemists were coming to terms with the idea that atoms combined in defined ways to make compounds with defined compositions. Berzelius’s chemical notation illustrating this proved so useful that it is still employed today.

Chemical notation provides immediate information to those who have taken the time to learn the code. Shown here are the formulas for three corrosive acids.