Teaching of chemistry before and after the periodic table

An Example of Teaching of Chemistry Before and After Mendeleev’s 1869 Periodic Table of Elements is presented. Prior to Mendeleev’s publication in 1869, only 63 elements were known. The ensuing discovery of the electron and the correspondence of the number of electrons to equivalent weight and atomic number is of singular importance to the impact of the Periodic Table of Elements and the way modern chemistry is taught. Without the identity of the electron and its alliance to atomic number, modern teaching of chemistry would be very different. Without it concepts of electronic configuration, oxidation and reduction, polarization, intermolecular interactions, types of bonding, Lewis acid/base definition, etc. would disappear in our vernacular. Thus, we trace the origin of the electron.