Short form periodic table(1869) This is based on the oldest periodic table, Mendeleev’s table. Elements with similar characteristics fall in vertical columns. Blank spaces exist for the undiscovered elements so that certain elements could be grouped together. 岩波講座 現代化学5「周期表の化学」 斉藤一夫 17ページ Long form periodic table(1905) Unlike a short form periodic table, each period is shown in a single vertical column. Although relevancies between the 1‐ 3 and 4‐7 periods are difficult to understand from this table, it is easy to understand vertical similarities. 岩波講座 現代化学5「周期表の化学」 斉藤一夫 16ページ Janet left‐step periodic table (1928) This table has a characteristic structure which shows a closer connection to the order of electron‐shell filling and quantum mechanics. The form of this table is more congruent with the order in which electron shells are filled, as shown in the accompanying sequence in the left margin (read from top to bottom, left to right). http://en.wikipedia.org/wiki/Periodic_table#Alternative_structures Pauling style periodic table(1950) Compared to the long form periodic table, it is easy to comprehend the relevancies between the 1‐3 and 4‐7 periods. On the other hand, it is a little hard to distinguish between typical elements and transition elements from this table. 岩波講座 現代化学5「周期表の化学」 斉藤一夫 18ページ Theodor Benfey's spiral periodic table (1960) The elements form a two‐dimensional spiral, starting from hydrogen, and folding their way around two peninsulas, the transition metals, and lanthanides and actinides. Benfey said that this table shows a beautiful step‐wise periodicity. http://en.wikipedia.org/wiki/Periodic_table#Alternative_structures