[Sanskrit eka, one.]
Dmitri Mendeleev (1834–1907), the Russian chemist who developed the periodic table, used this prefix to name elements that his scheme predicted but which were then unknown. He added it to the name of the preceding element in the same group: eka-selenium (now called technetium), eka-aluminium (now gallium). As all naturally occurring chemical elements have now been identified and named, the form is mostly of historical interest. It appears occasionally in names for previously unidentified transuranic elements (for example, eka-lead for element 114); however, a formal naming scheme for these exists, rendering the prefix unnecessary.