Actinium is a chemical element with the symbol Ac and atomic number 89. is the first element of the actinide series. All 36 known isotopes of actinium are radioactive. Ac 227 and 228 are naturally occurring isotopes with the half-life of 21.77 years and 6.13 hours respectively. It is 150 times more radioactive than radium. It is hazardous to health. If ingested, it gets deposited into the liver and bones, damaging the cells due to radioactive decay.
The element was discovered in 1899 by French chemist André-Louis Debierne, who made his discovery by isolating residue left by Marie and Pierre Curie in their extraction of radium from uranium ore.
Properties of Actinium
- It is a soft and silvery-white, radioactive, metallic element. Its estimated shear modulus is similar to that of lead. Owing to its strong radioactivity, Ac glows in the dark with a pale blue light, which originates from the surrounding air ionized by the emitted energetic particles.
- It has similar chemical properties to lanthanum and other lanthanides, and therefore these elements are difficult to separate when extracting from uranium ores. Solvent extraction and ion chromatography are commonly used for the separation.
- This radioactive element reacts with oxygen to form a white coating like substance called actinium oxide. Thus preventing the metal from further getting oxidized.
- As with most lanthanides and actinides, actinium exists in the oxidation state +3, and the Ac3+ ions are colorless in solutions.
- The oxidation state +3 originates from the [Rn]6d17s2 electronic configuration of actinium, with three valence electrons that are easily donated to give the stable closed-shell structure of the noble gas radon.
- The rare oxidation state +2 is only known for actinium dihydride (AcH2); even this may in reality be an electride compound like its lighter congener LaH2 and thus have actinium(III).
- Ac3+ is the largest of all known tripositive ions and its first coordination sphere contains approximately 10.9 ± 0.5 water molecules.