Atoms consist of three basic particles: protons, electrons, and neutrons. The nucleus (centre) of the atom contains the protons (positively charged) and the neutrons (no charge). The outermost regions of the atom are called electron shells and contain the electrons (negatively charged). Physics book, chapter 12, is about atoms where students learn about advanced concepts of atoms such as Rutherford’s model, Paschen series of spectral lines, etc.