|Name, symbol, number||actinium, Ac, 89|
|Group, period, block||n/a, 7, f|
|Standard atomic weight||(227) g·mol−1|
|Electron configuration||[Rn] 6d1 7s2|
|Electrons per shell||2, 8, 18, 32, 18, 9, 2 (Image)|
|Density (near r.t.)||10 g·cm−3|
|Melting point||(circa) 1323 K, 1050 °C, 1922 °F|
|Boiling point||3471 K, 3198 °C, 5788 °F|
|Heat of fusion||14 kJ·mol−1|
|Heat of vaporization||400 kJ·mol−1|
|Specific heat capacity||(25 °C) 27.2 J·mol−1·K−1|
|Electronegativity||1.1 (Pauling scale)|
|Ionization energies||1st: 499 kJ·mol−1|
|2nd: 1170 kJ·mol−1|
|Covalent radius||215 pm|
|Crystal structure||face-centered cubic|
|Magnetic ordering||no data|
|Thermal conductivity||(300 K) 12 W·m−1·K−1|
|CAS registry number||7440-34-8|
|Most stable isotopes|
|Main article: Isotopes of actinium|
Actinium (pronounced /ækˈtɪniəm/, ak-TIN-nee-əm) is a radioactive chemical element with the symbol Ac and atomic number 89, which was discovered in 1899. It was the first non-primordial radioactive element to be isolated. Polonium, radium and radon were observed before actinium, but they were not isolated until 1902. Actinium gave the name to the actinoid series, a group of 15 similar elements between actinium and lawrencium in the periodic table.
André-Louis Debierne, a French chemist, announced the discovery of a new element in 1899. He separated it from pitchblende and described the substance (in 1899) as similar to titanium and (in 1900) as similar to thorium. Friedrich Oskar Giesel independently discovered actinium in 1902 as a substance being similar to lanthanum and called it "emanium" in 1904. After a comparison of substances in 1904, Debierne's name was retained because it had seniority.
The stated history of the discovery of actinium remained questionable for decades. In publications starting in 1971 and continuing especially in 2000, it was shown that Debierne's published results in 1904 conflict with those in his articles published in 1899 and 1900.
The word actinium comes from the Greek aktis, aktinos (ακτίς, ακτίνος), meaning beam or ray.
Actinium is a silvery, radioactive, metallic element. Due to its intense radioactivity, actinium glows in the dark with a pale blue light. The chemical behavior of actinium is similar to that of the rare earth element lanthanum.
Actinium shows similar chemical behavior to lanthanum. Due to this similarity the separation of actinium from lanthanum and the other rare earth elements, which are also present in uranium ores was difficult. Solvent extraction and ion exchange chromatography was used for the separation. Only a limited number of actinium compounds are known, for example AcF3, AcCl3, AcBr3, AcOF, AcOCl, AcOBr, Ac2S3, Ac2O3 and AcPO4. All the mentioned compounds are similar to the corresponding lanthanum compounds and show that actinium compounds are generally in the oxidation state of +3.
Actinium is the first element of the actinoids and gave the group its name, similar to lanthanum for the lanthanoids. The group of elements is more diverse than the lanthanoids and therefore it took until 1945 when Glenn T. Seaborg proposed the most significant change to Mendeleev's periodic table, by introducing the actinoids.
Naturally occurring actinium is composed of 1 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 10.0 days, and 226Ac with a half-life of 29.37 h. All of the remaining radioactive isotopes have half-lives that are less than 10 hours and the majority of these have half-lives that are less than 1 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 2 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 successive decay products are part of the actinium series. The isotopes of actinium range in atomic weight from 206 u (206Ac) to 236 u (236Ac).
Actinium is found in trace amounts in uranium ore, but more commonly is 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°C.
Actinium 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. The actinium isotope 227Ac is a transient member of the actinium series decay chain, which begins with the parent isotope 235U (or 239Pu) and ends with the stable lead isotope 207Pb. Another actinium isotope (225Ac) is transiently present in the neptunium series decay chain, beginning with 237Np (or 233U) and ending with near-stable bismuth (209Bi).
225Ac is used in medicine to produce 213Bi in a reusable generator or can be used alone as an agent for radio-immunotherapy for Targeted Alpha Therapy (TAT). 225Ac was first produced artificially by the Institute for Transuranium Elements (ITU) in Germany using a cyclotron and by Dr Graeme Melville at St George Hospital in Sydney using a linac in 2000.
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 be fatal.
Actinium is a silver radioactivesolid metal. It is so radioactive that it glows in the dark. Even a small amount of actinium is dangerous to people.