Actinium Chemical Element

Actinium is a chemical element with the symbol Ac and atomic number 89. It was discovered in 1899 by French chemist André-Louis Debierne in pitchblende residues left after French physicists Pierre and Marie Curie had extracted radium from them, and it was also discovered in1902 independently by German chemist Friedrich Oskar Giesel. One tonne of natural uranium in ore contains about 0.2 milligrams of Ac-227, and one tonne of thorium contains about 5 nanograms of actinium-228.

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, It was one of the first non-primordial radioactive elements to be isolated.

Actinium Properties
Symbol Ac
Atomic Number 89
Atomic Mass 227 g mol -1
Discovered by Andre Debierne in 1899

Actinium-225 has a 10-day half-life, decaying by the emission of alpha particles. Its short-lived daughter isotopes emit only alpha and beta particles with no high-energy gamma rays. It is the prototype of a second rare-earth-like series, the actinoid elements.


Characteristics of Actinium

  • It is a soft, silvery-white, radioactive, metallic element. Its estimated shear modulus is similar to that of lead.
  • It has similar chemical properties to lanthanum and other lanthanides, and therefore these elements are difficult to separate when extracting from uranium ores.
  • Ac reacts rapidly with oxygen and moisture in air forming a white coating of actinium oxide that impedes further oxidation.
  • The oxidation state +3 originates from the [Rn]6d17s2 electronic configuration of actinium.

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