Chemistry attempts to understand transformations between substances. Central to this endeavor is the concept of an element. Elements are the building-blocks of chemistry: they survive chemical change, and chemical explanations track them from one composite substance to another, thereby explaining both the direction of chemical change and the properties of the substances they compose. The hypothesis that each element is characterized by a distinct kind of atom was controversial for most of the nineteenth century, but was broadly accepted in the twentieth century. During the same period, organic chemists developed structural formulae for chemical substances, although it was again controversial how seriously they were to be taken as representing the real arrangement of atoms in space connected by bonds. In the twentieth century there was a much closer interaction between chemistry and physics, with the application of quantum mechanics and experimental methods such as spectroscopy and X-ray crystallography, allowing deeper theoretical and empirical investigations of the molecular structures of substances. These chemical categories - element, substance, structure - remain indispensable to chemical explanation, and are central topics in the philosophical study of chemistry.
Hendry, R. F. (2013). Chemistry. In The Routledge Companion to Philosophy of Science (pp. 586–596). Taylor and Francis. https://doi.org/10.4324/9780203744857-66