3.1  The Periodic Law and the Periodic Table    Numbering Groups in the Periodic Table    Periods and Groups    Metals and Nonmetals    Atomic Number and Atomic Mass 3.2   Electron Arrangement and the Periodic Table    Valence Electrons    The Quantum Mechanical Atom    Energy Levels and Sublevels    Electron Configuration and the Aufbau Principle    Abbreviated Electron Configurations 3.3   The Octet Rule    Ion Formation and the Octet Rule 3.4   Trends in the Periodic Table    Atomic Size    Ion Size    Ionization Energy    Electron Affinity