chemical element with the atomic number of 89

Actinium is chemical element 89 on the periodic table. Its symbol is Ac. Actinium's mass is 227 g/mol.

Actinium,  89Ac
General properties
Pronunciation/ækˈtɪniəm/ (ak-TIN-ee-əm)
Appearancesilvery-white, glowing with an eerie blue light;[1] sometimes with a golden cast[2]
Mass number227 (most stable isotope)
Actinium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Atomic number (Z)89
Groupgroup 3
Periodperiod 7
Element category  actinide, sometimes considered a transition metal
Electron configuration[Rn] 6d1 7s2
Electrons per shell
2, 8, 18, 32, 18, 9, 2
Physical properties
Phase at STPsolid
Melting point1500 K ​(1227 °C, ​2240 °F) (estimated)[2]
Boiling point3500±300 K ​(3200±300 °C, ​5800±500 °F) (extrapolated)[2]
Density (near r.t.)10 g/cm3
Heat of fusion14 kJ/mol
Heat of vaporization400 kJ/mol
Molar heat capacity27.2 J/(mol·K)
Atomic properties
Oxidation states+2, +3 (a strongly basic oxide)
ElectronegativityPauling scale: 1.1
Ionization energies
  • 1st: 499 kJ/mol
  • 2nd: 1170 kJ/mol
  • 3rd: 1900 kJ/mol
  • (more)
Covalent radius215 pm
Color lines in a spectral range
Spectral lines of actinium
Other properties
Natural occurrencefrom decay
Crystal structureface-centered cubic (fcc)
Face-centered cubic crystal structure for actinium
Thermal conductivity12 W/(m·K)
CAS Number7440-34-8
Discovery and first isolationFriedrich Oskar Giesel (1902)
Named byAndré-Louis Debierne (1899)
Main isotopes of actinium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
225Ac trace 10 d α 221Fr
226Ac syn 29.37 h β 226Th
ε 226Ra
α 222Fr
227Ac trace 21.772 y β 227Th
α 223Fr
| references

Actinium is a silver radioactive, solid metal in actinide group. It is so radioactive that it glows in the dark. Even a small amount of actinium is dangerous to people.


Actinium was discovered in 1899 by André-Louis Debierne, a French chemist. In 1899, Debierne described the substance as similar to titanium[3] and (in 1900) as similar to thorium.[4]


Actinium is a soft, silvery-white, radioactive metal.[5][6] Its estimated shear modulus is similar to that of lead. Because its strong radioactivity, actinium glows in the dark with a pale blue light.[7]

Actinium reacts quickly with oxygen and moisture in air forming a white coating of actinium oxide that stops the actinium from oxidizing.[5]


Actinium that is found in nature is made up of two radionuclides 227Ac and 228Ac. Thirty-six radionuclides of actinium have been found. The most stable is 227Ac which has a half-life of 21.772 years. The shortest-lived known isotope of actinium is 217Ac which has a half-life of 69 nanoseconds.


Actinium is only found in trace amounts in uranium ores. For example, one tonne of uranium ore contains about 0.2 milligrams of 227Ac. Thorium ores contain about 5 nanograms of 228Ac per one tonne of thorium.[8]


225Ac is now being studied for use in cancer treatments. 227Ac is studied for use as an active element of radioisotope thermoelectric generators. 225Ac is used in medicine to make 213Bi in a reusable generator. It can be used in radiation therapy.[9][10][11]


  1. Wall, Greg (8 September 2003). "C&EN: It's Elemental: The Periodic Table - Actinium". C&EN: It's Elemental: The Periodic Table. Chemical and Engineering News. Retrieved 2 June 2011.
  2. 2.0 2.1 2.2 Kirby, Harold W.; Morss, Lester R. (2006). "Actinium". The Chemistry of the Actinide and Transactinide Elements. p. 18. doi:10.1007/1-4020-3598-5_2. ISBN 978-1-4020-3555-5.
  3. Debierne, André-Louis (1899). "Sur un nouvelle matière radio-active". Comptes rendus (in French). 129: 593–595.
  4. Debierne, André-Louis (1900–1901). "Sur un nouvelle matière radio-actif – l'actinium". Comptes rendus (in French). 130: 906–908.
  5. 5.0 5.1 Stites, Joseph G.; Salutsky, Murrell L.; Stone, Bob D. (1955). "Preparation of Actinium Metal 2". Journal of the American Chemical Society. 77 (1): 237–240. doi:10.1021/ja01606a085. ISSN 0002-7863.
  6. Solid state physics : advances in research and applications. Volume 16. Seitz, Frederick, 1911-2008., Turnbull, David, 1915-2007. New York: Academic Press. 1964. ISBN 978-0-08-086480-8. OCLC 646775097.CS1 maint: others (link)
  7. Katz, J J; Manning, W M (1952). "Chemistry of the Actinide Elements". Annual Review of Nuclear Science. 1 (1): 245–262. doi:10.1146/annurev.ns.01.120152.001333. ISSN 0066-4243.
  8. Hagemann, French (1950). "The Isolation of Actinium 1". Journal of the American Chemical Society. 72 (2): 768–771. doi:10.1021/ja01158a033. ISSN 0002-7863.
  9. CRC handbook of chemistry and physics. Lide, David R., 1928- (86th ed., 2005-2006 ed.). Boca Raton: CRC Press. 2005. ISBN 0-8493-0486-5. OCLC 61108810.CS1 maint: others (link)
  10. Deblonde, Gauthier J.-P.; Abergel, Rebecca J. (2016). "Active actinium". Nature Chemistry. 8 (11): 1084–1084. doi:10.1038/nchem.2653. ISSN 1755-4330.
  11. Boll, Rose A.; Malkemus, Dairin; Mirzadeh, Saed (2005). "Production of actinium-225 for alpha particle mediated radioimmunotherapy". Applied Radiation and Isotopes. 62 (5): 667–679. doi:10.1016/j.apradiso.2004.12.003.