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,...
Environmental Chemistry
Periodic Table of Elements: Gallium
A very detailed look at the element Gallium, a member of the Boron Group.
Environmental Chemistry
Periodic Table of Elements: Indium
A very detailed look at the element Indium, a member of the Boron Group.
Environmental Chemistry
Periodic Table of Elements: Thallium
A very detailed look at the element Thallium, a member of the Boron Group.
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.
Davidson College
Davidson College: Plot of First Ionization Energy and Atomic Number
Here you will find a group of images and graphs which plot covalent radii, first ionization energy, and electron affinity vs. atomic number.