Actinium

89 radium ← actinium → thorium La ↑ Ac ↓ Ute periodic table
General
Name, Symbol, Number	actinium, Ac, 89
Chemical series	actinides
Group, Period, Block	3, 7, f
Appearance	silvery
Atomic mass	(227) g/mol
Electron configuration	[Rn] 6d1 7s2
Electrons per shell	2, 8, 18, 32, 18, 9, 2
Physical properties
Phase	solid
Density (near r.t.)	10 g/cm³
Melting point	(circa) 1323 K (1050 °C, 1922 °F)
Boiling point	3471 K (3198 °C, 5788 °F)
Heat of fusion	14 kJ/mol
Heat of vaporization	400 kJ/mol
Heat capacity	(25 °C) 27.2 J/(mol·K)
Atomic properties
Crystal structure	cubic face centered
Oxidation states	3 (neutral oxide)
Electronegativity	1.1 (Pauling scale)
Ionization energies	1st: 499 kJ/mol
	2nd: 1170 kJ/mol
Atomic radius	195 pm
Miscellaneous
Magnetic ordering	no data
Thermal conductivity	(300 K) 12 W/(m·K)
CAS registry number	7440-34-8
Notable isotopes
Main article: Isotopes of actinium iso NA half-life DM DE (MeV) DP 225Ac syn 10 days α 5.935 221Fr 226Ac syn 29.37 hours β- 1.117 226Th ε 0.640 226Ra α 5.536 222Fr 227Ac 100% 21.773 years β- 0.045 227Th α 5.042 223Fr

Actinium (chemical symbol Ac, atomic number 89) is a silvery, radioactive, metallic element. Due to its intense radioactivity, it glows in the dark with a pale blue light. It is about 150 times as radioactive as radium and is therefore a valuable source of neutrons. Its isotope ²²⁵Ac is used in nuclear medicine.

Occurrence and production

Actinium is found in trace amounts in uranium ore, but it is more commonly made in milligram amounts by the neutron irradiation of ²²⁶Ra in a nuclear reactor. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300 ºC.

Etymology and history

The word actinium comes from the Greek aktis, aktinos, meaning beam or ray.

Actinium was discovered in 1899 by André-Louis Debierne, a French chemist, who separated it from pitchblende. Friedrich Oskar Giesel independently discovered actinium in 1902.

Notable characteristics

In the periodic table, actinium is situated in period seven and group three. It lies just below the rare earth lanthanum, and its chemical behavior is similar to that of lanthanum.

Actinium is often considered as the first of the actinides, which are a group of "inner transition metals." From the standpoint of their electronic structure, the actinides are characterized by the gradual filling of the 5f subshell. Actinium, however, has no electrons in its 5f subshell, and it best fits with the elements of group three.

It is found only in traces in uranium ores as ²²⁷Ac, an α and β emitter, with a half-life of 21.773 years. One ton of uranium ore contains about a tenth of a gram of actinium.

Isotopes

Naturally occurring actinium is composed of one radioactive isotope, ²²⁷Ac. 36 radioisotopes have been characterized with the most stable being ²²⁷Ac with a half-life of 21.772 y, ²²⁵Ac with a half-life of ten days, and ²²⁶Ac with a half-life of 29.37 h. All of the remaining radioactive isotopes have half-lives that are less than ten hours and the majority of these have half lives that are less than one minute. The shortest-lived isotope of actinium is ²¹⁷Ac which decays through alpha decay and electron capture. It has a half-life of 69 ns. Actinium also has two meta states.

Purified ²²⁷Ac comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.773-year half-life.

The isotopes of actinium range in atomic weight from 206 amu (²⁰⁶Ac) to 236 amu (²³⁶Ac).

Applications

Actinium is about 150 times as radioactive as radium, making it valuable as a neutron source. Otherwise, it has no significant industrial applications.

²²⁵Ac is used in medicine to produce ²¹³Bi in a reusable generator or can be used alone as an agent for radio-immunotherapy.

Precautions

²²⁷Ac is extremely radioactive, and in terms of its potential for radiation induced health effects, ²²⁷Ac is even more dangerous than plutonium. Ingesting even small amounts of ²²⁷Ac would present a serious health hazard.

See also

• Chemical element
• Lanthanum
• Metal
• Periodic table
• Inner transition metal

References

ISBN links support NWE through referral fees

• Actinium Los Alamos National Laboratory. Retrieved September 12, 2007.
• Chang, Raymond. Chemistry (9th ed.) New York: McGraw-Hill Science/Engineering/Math, 2006. ISBN 0073221031
• Cotton, F. Albert, and Geoffrey Wilkinson. Advanced Inorganic Chemistry, (4th ed.), New York: Wiley, 1980. ISBN 0-471-02775-8
• Greenwood, N.N. and A. Earnshaw. Chemistry of the Elements, (2nd Edition). Oxford, U.K.; Burlington, Massachusetts: Butterworth-Heinemann, Elsevier Science, 1998. ISBN 0750633654 Online version available at Knovel Retrieved September 12, 2007.

External links

All links retrieved June 15, 2023.

• Actinium WebElements.com.
• The Element Actinium Jefferson Lab.

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