The Wonders of the Periodic Table Element – Protactinium. Nestled within the complex arrangement of the periodic table, right next to uranium, lies a fascinating and notorious element: plutonium. Its atomic number is 94, and it bears the symbol Pu. But what makes plutonium so special? To start, plutonium is a man-made element, born out of humankind’s relentless pursuit of knowledge and power, a blend of science and ambition that has shaped the modern world in both awe-inspiring and terrifying ways.