This document discusses periodic trends in physical and chemical properties of elements. It explains that atomic radius and metallic character decrease moving left to right across a period and increase moving down a group. Graphs of atomic radii show this trend for main group elements. The document also states that properties of unknown elements can be predicted based on trends and properties of neighboring elements. Francium's properties are predicted based on other alkali metals. Finally, it predicts that barium chloride's formula is BaCl2 since calcium chloride is CaCl2 and they follow the same formula of MCl2.