The Elements by Theodore Gray!

Of all the periodic table apps, there is only one which Stephen Fry described as Alone worth the price of an iPad . The Elements is not just a reference app, it is a rich and engaging love story of the periodic table, told in words and pictures, and allowing you to experience the beauty and fascination of the building blocks of our universe in a way youve never seen before. Roald Hoffmann, writer and winner of the Nobel Prize for Chemistry