What characteristic of Mendeleev 's periodic table implicitly predicted the properties of elements that had not yet been discovered ?
He even predicted the likely properties of three yet - to - be - discovered elements , which he called ekaboron ( Eb ) , ekaaluminium ( Ea ) , and ekasilicon ( Es ) , which proved to be good predictors of the properties of scandium , gallium , and germanium , respectively , which each fill the spot in the periodic table assigned by Mendeleev .