Charge Density and Chemical Bonding

In the past 100 years, the Lewis diagram has frequently been challenged, modified, extended and rejected as being too simplistic. Those who teach chemistry to freshman, however, appreciate the diagram as one of the didactical rocks in the wild sea of ever developing science, because it is simple, easy to understand and long ranged in mediate basic chemistry. This article is aimed at the evaluation of the Lewis diagram in the light of modern charge density investigations and the topological analysis based on the quantum theory of atoms in molecules. Some old molecules like boranes, sulfate, and high-coordinate silicon will be revisited as well as some recent low-valent silicon species that were regarded impossible to make only some years ago. Can the Lewis diagram cope with new results from experiment and theory and be extended to “impossible” molecules? The answer is yes and that makes a model a good model: easy to adapt by and by and not suggesting any scientific dead ends, because the model might eventually be mistaken to be real from the inexperienced applicant.