In this lesson our instructor talks about periodic trends. First, he discusses the electron configuration of atoms and atomic radii. Then he talks about ionic radii, ionization energy, and electron affinity. He ends the lesson with a summary and two sample problems. Periodic Trends A consequence of quantum mechanics was the establishment of certain periodic trends, including ionization energy, electron affinity, atomic size and electronegativity. The periodic table is very organized and informative concerning an element’s physical and chemical properties. An atom’s electron configuration can be determined following the Aufbau Principle. Orbital box diagrams are drawn following the Pauli Exclusion Principle and Hund’s Rule.