The zigzag, staircase, line in the diagram of the periodic table above separates the metals, on the left, from non-metals, on the right. Hydrogen is a non-metal, but it is often put in the middle.

When the first periodic table was formulated by Mendeleev ... The official discovery of element-43 is accorded to Emilio Segrè and co-workers. Technetium, as they called it, was the last of ...