The Wonders of the Periodic Table Element - Actinium. Actinium, a curious name that sounds almost otherworldly, is an element that hails from a parallel universe of science and wonder. With the symbol "Ac" and the atomic number 89, Actinium holds a fascinating spot in the periodic table, nestled among the noble gases and other elements, telling a story that intertwines discovery, potential, and a sprinkle of mystery. Read More.