Mendeleev had predicted an atomic mass of 44 for ekaboron in 1871 while scandium has an atomic mass of 44.955910. Scandium was isolated as the oxide in spring, 1879, by Lars Fredrick Nilson Per Teodor Cleve recognized the correspondence and notified Mendeleev late in that year. Nowadays, the prefix eka- (and, more rarely, dvi-) is sometimes used in discussions about undiscovered elements, such as untriennium, a.k.a. Initial versions of the periodic table did not give the rare earth elements the treatment now given them, helping to explain both why Mendeleev’s predictions for heavier unknown elements did not fare as well as those for the lightest predictions and why they are not as well known or documented. The four predicted elements lighter than the rare earth elements, ekaboron ( Eb), ekaaluminum ( El), ekamanganese ( Em), and ekasilicon ( Es), proved to be good predictors of the properties of scandium, gallium, technetium and germanium respectively, which each fill the spot in the periodic table assigned by Mendeleev. To give provisional names to his predicted elements, Mendeleev used the prefixes eka-, dvi-, and tri-, from the Sanskrit words for one, two, and three, depending upon whether the predicted element was one, two, or three places down from the known element in his table with similar chemical properties. 3 Later predictions of elements coronium and ether.
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