ABSTRACT
It was during the nineteenth century that controversial models of molecular structure began to appear, made possible by the atomic theory of John Dalton (1766-1844), whose study of differential gas solubilities had led to a preoccupation with the characteristically different weights of chemically indivisible “atoms” and thence to the possibility of fixing the numbers of each elementary atom in specific compounds. Developments in the new science of organic chemistry, the articulation by Edward Frankland (1825-99) and August Kekulé (1829-96) of a theory of characteristic combining powers or “valency” for each element, the reformulation of Avogadro’s hypothesis by Stanislao Cannizzaro (1826-1910) in the late 1850s, and the concept of tetrahedrally directed bonds for the carbon atom, proposed independently by Joseph le Bel (1847-1930) and Jacobus van’t Hoff (1852-1911) in 1874, laid the classical foundations of a science that would henceforward strive to correlate chemical properties with molecular structure.
