10 Actinium Facts

Learn about the radioactive element actinium

Actinium is a radioactive metal and the first element in the actinide element group.
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Actinium is a radioactive metal that is the first element of the actinide series. It's sometimes considered the third element in Row 7 (last row) of the periodic table or in Group 3 (IIIB), depending on which chemist you ask. Here are 10 interesting facts about actinium.

10 Actinium Facts

  1. Actinium has atomic number 89, meaning each atom of the element has 89 protons. Its element symbol is Ac. It is an actinide, which also makes it a member of the rare earth element group, which is itself a subset of the transition metals group.
  1. Actinium was discovered in 1899 by French chemist Andre Debierne, who suggested the name for the element. The name comes from the Greek word aktinos or aktis, meaning "ray" or "beam". Debierne was a friend of Marie and Pierre Curie. Some sources suggest he worked with Marie Curie to discover actinium, using a pitchblende sample from which polonium and radium had already been extracted (discovered by the Curies).

    Actinium was independently discovered again in 1902 by German chemist Friedrich Giesel, who had not heard of Debierne's work. Giesel suggested the name emanium for the element, which comes from the word emanation, meaning "to emit rays".
  2. All isotopes of actinium are radioactive. It was the first non-primordial radioactive element to be isolated, even though other radioactive elements had been identified. Radium, radon, and polonium were discovered before actinium but weren't isolated until 1902.
  1. One of the more noteworthy actinium facts is that the element glows blue in the dark. The blue color comes from the ionization of gases in the air by radioactivity.
  2. Actinium is a silver-colored metal that has properties similar to those of lanthanum, the element located directly above it on the periodic table. The density of actinium is 10.07 grams per cubic centimeter. Its melting point is 1050.0°C and boiling point is 3200.0°C. Like other actinides, actinium readily tarnishes in the air (forming a white actinium oxide layer), is extremely dense, is highly electropositive, and likely forms numerous allotropes. The other actinides readily form compounds with nonmetals, although actinium compounds are not well-known.
  1. Although it is a rare natural element, actinium does occur in uranium ores, where it forms from the radioactive decay of uranium and other radioisotopes, such as radium. Actinium is present at an abundance of 0.0005 parts per trillion by mass in the Earth's crust. Its abundance in the solar system is negligible overall. There is about 0.15 mg of actinium per ton of pitchblende.
  2. Although it is found in ores, actinium is not commercially extracted from minerals. High-purity actinium may be made by bombarding radium with neutrons, causing the radium to decay in a predictable fashion into actinium. The primary use of the metal is for research purposes. It is valuable neutron source because of its high activity level. Ac-225 may be used for cancer treatment. Ac-227 may be used for thermoelectric generators, as for spacecraft.
  3. 36 isotopes of actinium are known—all radioactive. Actinium-227 and actinium-228 are the two that occur naturally. The half-life of Ac-227 is 21.77 years, while the half-life of Ac-228 is 6.13 hours.
  4. One interesting factoid is that actinium is about 150 times more radioactive than radium!
  5. Actinium presents a health hazard. If ingested, it is deposited into the bones and the liver, where radioactive decay damages cells, potentially leading to bone cancer or other illnesses.