The Path to the Periodic Table
The path to the periodic table began early in the 19th century, when John Dalton united the atomic theory of matter, which had existed in various forms since antiquity, with the concept of the chemical element, which had emerged in the late 18th century with the work of Antoine-Laurent Lavoisier and his followers. On the basis of his newly synthesized theory, Dalton calculated the first relative weights of atoms and compounds. Although the method for calculating atomic weights was disputed for another 50 years, in the long run atomic weights would provide the key means of organizing the elements into the periodic table.
John Dalton was a schoolteacher, a meteorologist, and an expert on color blindness, but he is best known for his theory of atomism, the foundation of our modern concept of the atom.
Amedeo Avogadro hypothesized that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. From this it followed that relative molecular weights of any two gases are the same as the ratio of the densities of the two gases under the same conditions of temperature and pressure.
In 1858 Stanislao Cannizzaro outlined a course in theoretical chemistry for students at the University of Genoa. His outline, which employed the ideas of Amedeo Avogadro, later became a pathway out of the confusion rampant among chemists about atomic weights and the fundamental structure of chemical compounds.
In 1860 Robert Bunsen and Gustav Kirchhoff discovered two alkali metals, cesium and rubidium, with the aid of the spectroscope they had invented the year before. These discoveries inaugurated a new era in the means used to find new elements.
For both Julius Meyer and Dmitri Mendeleev, writing a textbook proved to be the impetus for developing the periodic table—a device to present the more than 60 elements known at the time in an intelligible fashion.
The Scottish chemist William Ramsay is known for work that established a whole new group in the periodic table, variously called over time the inert, rare, or noble gases.
Theodore Richards, the first American to be awarded the Nobel Prize in chemistry, received it in 1914 for his accurate determinations of atomic weights—25 in all.