Periodic table

[Rennhack]

An arrangement of chemical elements in order of increasing atomic number. Elements of similar properties are placed one under the other, yielding groups or families of elements. Within each group, there is a variation of chemical and physical properties, but in general, there is a similarity of chemical behavior within each group.

NukeWorker has interactive periodic Tables, below are links to them.  We also have regular tables like the one pictured below.
http://www.nukeworker.com/pictures/displayimage_424_3.html