Chemists soon noticed patterns when they grouped elements into sets of three by atomic weight. Such experiments offered glimpses of an order within the elemental universe. But the work was frustrating. Other chemists pressed on. As atomic weights grew more accurate, more patterns emerged.
In , the German chemist Julius Lothar Meyer published a table of twenty-eight elements. Five years later, Mendeleev published his own periodic table, which steadily evolved into the version we use today. Like Meyer, Mendeleev had organized his particles into a rough grid, its rows containing elements with similar properties. But he also garnished his table with many tempting question marks and empty spaces, and made explicit elemental prophecies.
Mendeleev accurately predicted the existence of then-undiscovered elements, such as gallium and germanium, and foretold their interactions with other elements. But, Scerri explains, the Russian chemist was a master storyteller and, compared to Meyer and other competitors, a more effective evangelist for the periodic system.
Mendeleev took every opportunity to argue, at times heedlessly, that the characteristics of the elements repeat in an orderly and predictable way. He was both indefatigable and inflexible, at least until the tide of scientific opinion turned against him. In the late eighteen-fifties, scientists found that the elemental makeup of a given substance could be deduced from the light that it gave off when set ablaze; in , a French astronomer, Jules Janssen, used the technique to discover helium element No.
At first, Mendeleev argued that helium could not exist; it had no place on the periodic table. But, around the turn of the twentieth century, after the other noble gases had been discovered and shown to share properties with helium, other scientists made a column just for them, and Mendeleev fell in line.
The column runs along the right, with helium poking out on top. Over the past century and a half, our ideas about the universe have changed drastically. But the basic format of the periodic table has endured. This last model placed uranium at its base, under the assumption that chemistry would never encounter a bigger atom.
But the elemental ceiling has continued to rise. Early element hunters had used fire to distill their elements, or else mixed minerals with boiling acid. Those techniques were replaced, in the twentieth century, by technologies that used electricity to shake atoms into pieces. Scientists, moreover, realized that atoms have structures, made up of protons, neutrons, and electrons; those structures can fall apart or get bigger.
These developments fundamentally changed our relationship to matter. Discovering an element used to be like finding Dr. Livingstone in East Africa: you knew he was there somewhere. Now the line between discovering and creating blurred. For example, he changed the weight of beryllium from 14 to 9. This placed beryllium into Group 2 above magnesium whose properties it more closely resembled than where it had been located above nitrogen.
In all Mendeleev found that 17 elements had to be moved to new positions from those indicated strictly by atomic weight for their properties to correlate with other elements.
These changes indicated that there were errors in the accepted atomic weights of some elements atomic weights were calculated from combining weights, the weight of an element that combines with a given weight of a standard.
However, even after corrections were made by redetermining atomic weights, some elements still needed to be placed out of order of their atomic weights. From the gaps present in his table, Mendeleev predicted the existence and properties of unknown elements which he called eka-aluminum, eka-boron, and eka-silicon.
The elements gallium, scandium and germanium were found later to fit his predictions quite well. In addition to the fact that Mendeleev's table was published before Meyers', his work was more extensive predicting new or missing elements.
In all Mendeleev predicted the existence of 10 new elements, of which seven were eventually discovered -- the other three, atomic weights 45, and do not exist.
He also was incorrect in suggesting that the element pairs of argon-potassium, cobalt-nickel and tellurium-iodine should be interchanged in position due to inaccurate atomic weights. Updated October 03, Featured Video. Cite this Article Format. Helmenstine, Anne Marie, Ph. Element Discovery Timeline. Livermorium Facts - Element or Lv.
Rutherfordium Facts - Rf or Element Overview of Dubnium Facts and Physical Properties. Scientists Complete the Periodic Table. Seaborg Joseph W. Kennedy Edward M. McMillan Arthur C. Auer von Welsbach Promethium Jacob A. Marinsky Lawrence E.
Glendenin Charles D. Coryell Protactinium Kasimir Fajans O. Oganessian et. Zirconium Martin Heinrich Klaproth
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