The Royal Society of Chemistry have launched a free online periodic table where you can easily locate:
- atomic number and mass
- key isotopes
- electron configuration
- first ionisation energy
On the RSC table you can also click on each element to get more detailed information about bonding, isotopes, usage, etc., along with a link to a podcast about the element. Other features include a slide bar to show the state of each element at specific temperatures, and information about which elements were known about in given year.