Procedures used to calculate atomic radii are discussed. Hundreds of periodic tables on the Web provide atomic numbers, atomic weights, and element symbols. The discovery dates and discoverers of chemical elements are given on this partially complete periodic table. Includes a bibliography. Energy levels, transition probabilities, and wavelengths for atomic line spectra.
Ionization energies for neutral atoms are also available on a hyperlinked periodic table.
A set of presentation slides and a movie introducing the electron sea model of metals. The files are very large and the site is not recommended if you have a slow connection. This excellent periodic table contains images of element samples and a searchable database of element information that is extensive but not overwhelming. The quintessential element database.