Presenting basic atomic theory as given in first and second year courses at university, this text demonstrates that the structure of the Periodic Table as we know it is based on sound principles. Theoretical concepts are presented throughout the book, along with the experimental evidence for them. Foundations are laid in the introductory chapter, which deals with fundamental particles, electromagnetic radiation and Heisenberg’s Uncertainty Principle. Atomic orbitals are then described, using a minimum of mathematics, followed by a discussion of the electron configurations of the elements. Further chapters reveal the relationships between the electronic configurations of the elements and some properties of their atoms; and the variations in the properties of their fluorides and oxides across the periods and down the groups of the Periodic Table.