ActiniumIII

Actinium(III) refers to the trivalent ion of actinium, Ac3+, the predominant oxidation state for actinium in aqueous solution and in many solid compounds. In water, Ac3+ forms a highly hydrated aquo complex, commonly represented as [Ac(H2O)9]3+. As a large, hard trivalent cation, it readily forms salts such as AcCl3, Ac2(SO4)3 and Ac(NO3)3, and it hydrolyzes at modest pH to oxo- and hydroxy- species, including actinium oxide and basic acetates.

Occurrence and production: Actinium is extremely rare in the Earth's crust and is not found in appreciable quantities as a free element. It occurs at trace levels in uranium- and thorium-bearing minerals and is typically produced as a decay product of other actinides or by irradiation of thorium or radium in reactors.

Isotopes and hazards: All actinium isotopes are radioactive. The longest-lived naturally occurring isotope is 227Ac (half-life about 21.8 years); 225Ac (about 10 days) and 223Ra are notable for medical research applications. Because of radioactivity and chemical toxicity, handling requires specialized facilities and protocols.

Applications and research: Due to scarcity and radioactivity, commercial uses are limited. Actinium is mainly studied in radiochemistry and nuclear science. Actinium-225 is under investigation for targeted alpha-particle therapies in oncology.

History: Actinium was discovered in 1899 by André Debierne in pitchblende. The name derives from the Greek aktis, meaning ray, in reference to its intense radioactivity.