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Brief History: The Periodic Table

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DK Limited/Corbis

A Russian periodic table based on Dmitri Mendeleyevĺs original table of 1869.

Six atoms may seem minuscule--especially if they exist for only fractions of a second--but they can have huge implications. The recent announcement that Russian and American scientists finally managed to produce a tiny bit of element 117 by firing calcium atoms (element 20) at berkelium (element 97) fills in a missing spot on the periodic table. When the results are confirmed, "ununseptium" will get a catchier moniker and occupy the square between 116 and 118--elements that also await proper names from the International Union of Pure and Applied Chemistry.

We've come a long way from the classical list of earth, wind, water and fire. Modern elements, with all their complexities, require a chart whose rows and columns reflect their properties and how they interact with one another. In the 19th century, several scientists worked on developing a periodic table that arranged the elements according to their atomic weight. It is Russian chemistry professor Dmitri Mendeleev, however, who is credited with developing the first real table in 1869. He organized the 63 then known elements into groups with similar properties and left some spaces blank for those whose existence he could not yet prove. In 1913 physicist Henry Moseley's experiments showed definitively that the order was dependent not on atomic weight but on atomic number--the number of protons in an atom's nucleus.

Like most of those after uranium (element 92), "ununseptium" is artificially made. This latest find supports the idea that as-yet-undiscovered stable elements exist, but no one knows for sure if there is an end point to the table or if additional artificially engineered elements will expand it even further. The question of how much bigger the 141-year-old chart can get is anything but elementary.