Graphic representations of three-dimensional structures play a pivotal role both in academic research and chemical education. Nevertheless, their deceptive simplicity can lead school and even university students to an incorrect understanding of these representations that are central for both organic and inorganic chemistry. A deep knowledge of their symbolic meaning is, indeed, essential to avoid a meaningless learning of the discipline. Two important historical examples, the three-dimensional representations of tetrahedral carbon and the geometry of metal complexes, are discussed in this paper. More in detail, this work investigates the way in which these three-dimensional formulae were received and presented in school and university textbooks published in the late 19th and early 20th centuries, before the introduction of techniques of structural investigation such as X-ray crystallography. Given the difficulty of finding all textbooks published in that period worldwide, the creation of a freely accessible database is also encouraged. Generally underestimated in historical investigations, old chemistry manuals are, in fact, essential to understand how the discipline has been taught in the past.
Matteo Chioccioli (Thu,) studied this question.