Actinium
Actinium is a chemical element with symbol Ac and atomic number 89. It was discovered by Friedrich Oskar Giesel in 1902, who isolated the element the same year. Actinium gave the name to the actinide series, a group of 15 similar elements between actinium and lawrencium in the periodic table. It is also sometimes considered the first of the 7th-period transition metals, although lawrencium is less commonly given that position. Together with polonium, radium, and radon, actinium was one of the first non-primordial radioactive elements to be isolated. MORE
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