The Periodic Table of Elements hasn't always looked like it does now, a well-organized chart arranged by atomic number. In the mid-nineteenth century, chemists were of the belief that the elements should be sorted by atomic weight. However, the weights of many elements were calculated incorrectly, and over time it became clear that not only did the elements need rearranging, but that the periodic table contained many gaps and omissions: there were elements yet to be discovered, and the allure of finding one had scientists rushing to fill in the blanks. Supposed "discoveries" flooded laboratories, and the debate over what did and did not belong on the periodic table reached a fever pitch. With the discovery of radioactivity, the discourse only intensified. Throughout its formation, the Periodic Table of Elements has seen false entries, good-faith errors, retractions, and dead ends. In fact, there have been more falsely proclaimed elemental discoveries throughout history than there are elements on the table as we know it today. The Lost Elements: The Periodic Table's Shadow Side collects the most notable of these instances, stretching from the nineteenth century to the present. The book tells the story of how scientists have come to understand elements, by discussing the failed theories and false discoveries that shaped the path of scientific progress. We learn of early chemists' stubborn refusal to disregard alchemy as a legitimate practice, and of one German's supposed discovery of an elemental metal that breathed. As elements began to be created artificially in the twentieth century, we watch the discovery climate shift to favor the physicists, rather than the chemists. Along the way, Fontani, Costa, and Orna introduce us to the key figures in the development of today's periodic table, including Lavoisier and Mendeleev. Featuring a preface from Nobel Laureate Roald Hoffmann, The Lost Elements is an expansive history of the wrong side of chemical discovery-and reveals how these errors and gaffes have helped shape the table as much as any other form of scientific progress.