Actinium, ₈₉Ac

Actinium
Pronunciation	/ækˈtɪniəm/ ​(ak-TIN-ee-əm)
Appearance	silvery-white, glowing with an eerie blue light;[1] sometimes with a golden cast[2]
Mass number
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 La ↑ Ac ↓ — radium ← actinium → thorium
Atomic number (Z)	89
Group	f-block groups (no number)
Period	period 7
Block	f-block
Electron configuration	[Rn] 6d1 7s2
Electrons per shell	2, 8, 18, 32, 18, 9, 2
Physical properties
Phase at STP	solid
Melting point	1500 K ​(1227 °C, ​2240 °F) (estimated)[2]
Boiling point	3500±300 K ​(3200±300 °C, ​5800±500 °F) (extrapolated)[2]
Density (near r.t.)	10 g/cm3
Heat of fusion	14 kJ/mol
Heat of vaporization	400 kJ/mol
Molar heat capacity	27.2 J/(mol·K)
Atomic properties
Oxidation states	+3 (a strongly basic oxide)
Electronegativity	Pauling scale: 1.1
Ionization energies	1st: 499 kJ/mol 2nd: 1170 kJ/mol 3rd: 1900 kJ/mol (more)
Covalent radius	215 pm
Spectral lines of actinium
Other properties
Natural occurrence	from decay
Crystal structure	​face-centered cubic (fcc) (cF4)
Lattice constant	a = 531.5 pm (at 20 °C)[3]
Thermal conductivity	12 W/(m⋅K)
CAS Number	7440-34-8
History
Discovery and first isolation	Friedrich Oskar Giesel (1902, 1903)
Named by	André-Louis Debierne (1899)
Isotopes of actinium v e
Main isotopes[4] Decay abun­dance half-life (t1/2) mode pro­duct 225Ac trace 9.919 d α 221Fr CD 211Bi 226Ac synth 29.37 h β− 226Th ε 226Ra α 222Fr 227Ac trace 21.772 y β− 227Th α 223Fr
Category: Actinium view talk edit | references

Actinium is a chemical element; it has symbol Ac and atomic number 89. It was first isolated by Friedrich Oskar Giesel in 1902, who gave it the name emanium; the element got its name by being wrongly identified with a substance André-Louis Debierne found in 1899 and called actinium. Actinium gave the name to the actinide series, a set of 15 elements between actinium and lawrencium in the periodic table. Together with polonium, radium, and radon, actinium was one of the first non-primordial radioactive elements to be isolated.

A soft, silvery-white radioactive metal, actinium reacts rapidly with oxygen and moisture in air forming a white coating of actinium oxide that prevents further oxidation. As with most lanthanides and many actinides, actinium assumes oxidation state +3 in nearly all its chemical compounds. Actinium is found only in traces in uranium and thorium ores as the isotope ²²⁷Ac, which decays with a half-life of 21.772 years, predominantly emitting beta and sometimes alpha particles, and ²²⁸Ac, which is beta active with a half-life of 6.15 hours. One tonne of natural uranium in ore contains about 0.2 milligrams of actinium-227, and one tonne of thorium contains about 5 nanograms of actinium-228. The close similarity of physical and chemical properties of actinium and lanthanum makes separation of actinium from the ore impractical. Instead, the element is prepared, in milligram amounts, by the neutron irradiation of ²²⁶Ra in a nuclear reactor. Owing to its scarcity, high price and radioactivity, actinium has no significant industrial use. Its current applications include a neutron source and an agent for radiation therapy.

History

André-Louis Debierne, a French chemist, announced the discovery of a new element in 1899. He separated it from pitchblende residues left by Marie and Pierre Curie after they had extracted radium. In 1899, Debierne described the substance as similar to titanium^[5] and (in 1900) as similar to thorium.^[6] Friedrich Oskar Giesel found in 1902^[7] a substance similar to lanthanum and called it "emanium" in 1904.^[8] After a comparison of the substances' half-lives determined by Debierne,^[9] Harriet Brooks in 1904, and Otto Hahn and Otto Sackur in 1905, Debierne's chosen name for the new element was retained because it had seniority, despite the contradicting chemical properties he claimed for the element at different times.^[10][11]

Articles published in the 1970s^[12] and later^[13] suggest that Debierne's results published in 1904 conflict with those reported in 1899 and 1900. Furthermore, the now-known chemistry of actinium precludes its presence as anything other than a minor constituent of Debierne's 1899 and 1900 results; in fact, the chemical properties he reported make it likely that he had, instead, accidentally identified protactinium, which would not be discovered for another fourteen years, only to have it disappear due to its hydrolysis and adsorption onto his laboratory equipment. This has led some authors to advocate that Giesel alone should be credited with the discovery.^[2] A less confrontational vision of scientific discovery is proposed by Adloff.^[13] He suggests that hindsight criticism of the early publications should be mitigated by the then nascent state of radiochemistry: highlighting the prudence of Debierne's claims in the original papers, he notes that nobody can contend that Debierne's substance did not contain actinium.^[13] Debierne, who is now considered by the vast majority of historians as the discoverer, lost interest in the element and left the topic. Giesel, on the other hand, can rightfully be credited with the first preparation of radiochemically pure actinium and with the identification of its atomic number 89.^[12]

The name actinium originates from the Ancient Greek aktis, aktinos (ακτίς, ακτίνος), meaning beam or ray.^[14] Its symbol Ac is also used in abbreviations of other compounds that have nothing to do with actinium, such as acetyl, acetate^[15] and sometimes acetaldehyde.^[16]

Properties

Actinium is a soft, silvery-white,^[17][18] radioactive, metallic element. Its estimated shear modulus is similar to that of lead.^[19] Owing to its strong radioactivity, actinium glows in the dark with a pale blue light, which originates from the surrounding air ionized by the emitted energetic particles.^[20] Actinium has similar chemical properties to lanthanum and other lanthanides, and therefore these elements are difficult to separate when extracting from uranium ores. Solvent extraction and ion chromatography are commonly used for the separation.^[21]

The first element of the actinides, actinium gave the set its name, much as lanthanum had done for the lanthanides. The actinides are much more diverse than the lanthanides^[22] and therefore it was not until 1945 that the most significant change to Dmitri Mendeleev's periodic table since the recognition of the lanthanides, the introduction of the actinides, was generally accepted after Glenn T. Seaborg's research on the transuranium elements^[23] (although it had been proposed as early as 1892 by British chemist Henry Bassett).^[24]

Actinium reacts rapidly with oxygen and moisture in air forming a white coating of actinium oxide that impedes further oxidation.^[17] As with most lanthanides and actinides, actinium exists in the oxidation state +3, and the Ac³⁺ ions are colorless in solutions.^[25] The oxidation state +3 originates from the 6d¹7s² electronic configuration of actinium, with three valence electrons that are easily donated to give the stable closed-shell structure of the noble gas radon.^[18] Although the 5f orbitals are unoccupied in an actinium atom, it can be used as a valence orbital in actinium complexes and hence it is generally considered the first 5f element by authors working on it.^[26][27][28] Ac³⁺ is the largest of all known tripositive ions and its first coordination sphere contains approximately 10.9 ± 0.5 water molecules.^[29]

Chemical compounds

Due to actinium's intense radioactivity, only a limited number of actinium compounds are known. These include: AcF₃, AcCl₃, AcBr₃, AcOF, AcOCl, AcOBr, Ac₂S₃, Ac₂O₃, AcPO₄ and Ac(NO₃)₃. They all contain actinium in the oxidation state +3.^[25][30] In particular, the lattice constants of the analogous lanthanum and actinium compounds differ by only a few percent.^[30]

Here a, b and c are lattice constants, No is space group number and Z is the number of formula units per unit cell. Density was not measured directly but calculated from the lattice parameters.

Oxides

Actinium oxide (Ac₂O₃) can be obtained by heating the hydroxide at 500 °C or the oxalate at 1100 °C, in vacuum. Its crystal lattice is isotypic with the oxides of most trivalent rare-earth metals.^[30]

Halides

Actinium trifluoride can be produced either in solution or in solid reaction. The former reaction is carried out at room temperature, by adding hydrofluoric acid to a solution containing actinium ions. In the latter method, actinium metal is treated with hydrogen fluoride vapors at 700 °C in an all-platinum setup. Treating actinium trifluoride with ammonium hydroxide at 900–1000 °C yields oxyfluoride AcOF. Whereas lanthanum oxyfluoride can be easily obtained by burning lanthanum trifluoride in air at 800 °C for an hour, similar treatment of actinium trifluoride yields no AcOF and only results in melting of the initial product.^[30][36]

AcF₃ + 2 NH₃ + H₂O → AcOF + 2 NH₄F

Actinium trichloride is obtained by reacting actinium hydroxide or oxalate with carbon tetrachloride vapors at temperatures above 960 °C. Similar to oxyfluoride, actinium oxychloride can be prepared by hydrolyzing actinium trichloride with ammonium hydroxide at 1000 °C. However, in contrast to the oxyfluoride, the oxychloride could well be synthesized by igniting a solution of actinium trichloride in hydrochloric acid with ammonia.^[30]

Reaction of aluminium bromide and actinium oxide yields actinium tribromide:

Ac₂O₃ + 2 AlBr₃ → 2 AcBr₃ + Al₂O₃

and treating it with ammonium hydroxide at 500 °C results in the oxybromide AcOBr.^[30]

Other compounds

Actinium hydride was obtained by reduction of actinium trichloride with potassium at 300 °C, and its structure was deduced by analogy with the corresponding LaH₂ hydride. The source of hydrogen in the reaction was uncertain.^[37]

Mixing monosodium phosphate (NaH₂PO₄) with a solution of actinium in hydrochloric acid yields white-colored actinium phosphate hemihydrate (AcPO₄·0.5H₂O), and heating actinium oxalate with hydrogen sulfide vapors at 1400 °C for a few minutes results in a black actinium sulfide Ac₂S₃. It may possibly be produced by acting with a mixture of hydrogen sulfide and carbon disulfide on actinium oxide at 1000 °C.^[30]

Isotopes

Naturally occurring actinium is principally composed of two radioactive isotopes; ²²⁷
Ac (from the radioactive family of ²³⁵
U) and ²²⁸
Ac (a granddaughter of ²³²
Th). ²²⁷
Ac decays mainly as a beta emitter with a very small energy, but in 1.38% of cases it emits an alpha particle, so it can readily be identified through alpha spectrometry.^[2] Thirty-three radioisotopes have been identified, the most stable being ²²⁷
Ac with a half-life of 21.772 years, ²²⁵
Ac with a half-life of 10.0 days and ²²⁶
Ac with a half-life of 29.37 hours. All remaining radioactive isotopes have half-lives that are less than 10 hours and the majority of them have half-lives shorter than one minute. The shortest-lived known isotope of actinium is ²¹⁷
Ac (half-life of 69 nanoseconds) which decays through alpha decay. Actinium also has two known meta states.^[38] The most significant isotopes for chemistry are ²²⁵Ac, ²²⁷Ac, and ²²⁸Ac.^[2] Zdroj:https://en.wikipedia.org?pojem=Emanium
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