General periodic trends are specific patterns that are present within the periodic table; these are patterns in properties like electronegativity, ionization energy, electron affinity, atomic radius, melting point, and metallic character. General periodic trends provide chemists with an invaluable tool to quickly predict an element's properties. These trends exist because of the similar atomic structure of the elements within their respective group families or periods, and because of the periodic nature of the elements. Some of the general periodic trends are described in this section. 2.3.1: Ionization energy Ionization energy (IE) is the energy required to remove an electron from a neutral atom or cation in its gaseous phase. IE is also known as ionization potential. 2.3.2: Electron Affinity 2.3.3: Covalent and Ionic Radii The page discusses various methods for measuring the radii of atoms and ions, including nonpolar atomic radii, van der Waals radii, and crystal radii determined from X-ray data. It explains how atomic radii generally decrease across a period due to increasing nuclear charge, while atomic size increases down a group due to higher quantum levels. References Russo, Steve, and Mike Silver. Introductory Chemistry. San Francisco: Pearson, 2007. Petrucci, Ralph H, et al. General Chemistry: Principles and Modern Applications. 9th Ed. New Jersey: Pearson, 2007. Atkins, Peter et. al, Physical Chemistry , 7 th Edition, 2002, W.H Freeman and Company, New York, pg. 390. Alberty, Robert A. et. al, Physical Chemistry , 3 rd Edition, 2001, John Wiley & Sons, Inc, pg. 380. Kots, John C. et. al, Chemistry & Chemical Reactivity , 5 th Edition, 2003, Thomson Learning Inc, pg. 305-309.