The pre-quantum atomic theory told by experiments

A survey was conducted among chemistry students and graduates of any level about atomic theory before quantum. The incorrect answers recorded show the students have many misconceptions about the origin of atomic theory and how the existence of atoms and molecules was first demonstrated. These results have suggested a clarification on the subject is needed. Here, the basic concepts of atomic theory are told again, presenting the historical crucial experimental demonstrations with vapor densities, elemental analysis, and calorimetry, based on Avogadro and Cannizzaro's main works. The article addresses those who want to fill in their missing knowledge on this subject or to fix incorrect ideas. The article is also proposed as a guideline for chemistry teachers who wish to implement those experimental demonstrations in their laboratory classes, which is highly recommended to avoid atomic theory misconceptions to persist in future chemistry graduates.