Chem Tutor
Chem Tutor: Atomic Structure: Atomic Weights and Atomic Numbers
This lesson explains many basic concepts of atomic structure. It starts with atomic mass and number and then works up to more sophisticated information on electron configuration and how each element fits into the Periodic Table.
Encyclopedia of Earth
Encyclopedia of Earth: Elements
Engaging and very informative article that explains what elements are, some of their history, how they are represented, the categories of elements, the periodic table, and how they are structured and classified.
Lawrence Berkeley National Laboratory
Berkeley Lab: Basic Nuclear Science Information
Site provides the ABC's of nuclear science including radioactivity and gamma decay to fission and comic rays.