As a teacher of physical chemistry, I noticed that students, even in advanced classes, have difficulties in understanding the basics of redox chemistry. In this Section 2, I attempted to summarize some fundamental principles related to electrons, including the atomic structure, periodic table, main electronic models, electronic configuration, and the energy levels of electrons. The identification of the electronic configurations of elements and visualization of electrons in their outer shells are very important concepts in understanding redox processes. To further clarify the discussed concepts, numerous questions and problems with detailed answers are provided. Most of these questions are formulated by students like you. I believe that this Section 2 would greatly help students with levels varying from high school to advanced university classes.