Simon Fraser University
Chem1 Virtual Textbook: Sizes of Atoms and Ions
Acting as a subtopic of the General Chemistry Virtual Textbook's section on Atoms and the Periodic Table, this site seeks to answer the question, What do we mean by the "size" of an atom? Terms such as metallic radius, covalent radius,...
Wikimedia
Wikipedia: Atomic Radius
This site from the encyclopedia Wikipedia provides a basic definition for what the atomic radius is, and an explanation of what covalent and metallic radii are.