Physicists have filled in some longtime blank spaces on the periodic table, calculating electron affinities of the lanthanides, a series of 15 elements known as rare earths. Physicists at Michigan ...

Predictive power. Gallium. Mendeleev left blank spaces in his original periodic table so that he could properly line up the known elements. Gallium, element 31, was his first gap to be filled, in ...

This video excerpt from NOVA's "Hunting the Elements" explains why some elements are more reactive than others.