Google Research built an interactive periodic table of the elements where you can see the relative amounts of the elements as found in the human body, in the sea, and, most interestingly, by the number of mentions in books.
If you've ever wondered why the periodic table is shaped the way it is, click on "electrons" under "Shape" and pay attention to the number of electrons in the outer shells in each column of elements. Amazingly, when Dmitri Mendeleev and German chemist Julius Meyer published the first periodic tables in 1869/1870, the elements were organized only by atomic weights and chemical properties; they didn't know what an electron was and certainly weren't aware of quantum shells of electrons. (via @djacobs)
