Actinium is a chemical element with the symbol Ac and atomic number 89. It was first isolated by Friedrich Oskar Giesel in 1902, who gave it the name emanium. The element got its name by being wrongly identified with a substance André-Louis Debierne found and called actinium.

Actinide Chemical Elements

The actinide series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.

These fifteen actinide elements [Actinium (Ac), Thorium (Th), Protactinium (Pa), Uranium (U), Neptunium (Np), Plutonium (Pu), Americium (Am), Curium (Cm), Berkelium (Bk), Californium (Cf), Einsteinium (Es), Fermium (Fm), Mendelevium (Md), Nobelium (No), Lawrencium (Lr)], have very large atomic and ionic radii and exhibit an unusually large range of physical properties.