# Actinium

properties
[ Rn ] 6 d 1 7 s 2
89 Ac
General
Name , symbol , atomic number Actinium, Ac, 89
Element category Transition metals
Group , period , block 3 , 7 , d
Appearance silvery
CAS number 7440-34-8
Mass fraction of the earth's envelope 6 · 10 −14  ppm
Atomic
Atomic mass 227.0278 u
Electron configuration [ Rn ] 6 d 1 7 s 2
1. Ionization energy 5.380 226 (24) eV 519.11 kJ / mol
2. Ionization energy 11.75 (3) eV1 134 kJ / mol
3. Ionization energy 17th.431 (20) eV1 682 kJ / mol
4. Ionization energy 44.8 (1.4 eV)4 320 kJ / mol
5. Ionization energy 55.0 (1.9) eV5 310 kJ / mol
Physically
Physical state firmly
Crystal structure Cubic area-centered
density 10.07 g / cm 3
Melting point 1323 K (1050 ° C)
boiling point 3573 (3300 ° C)
Molar volume 22.55 · 10 −6 m 3 · mol −1
Heat of evaporation 400 kJ / mol
Heat of fusion 14 kJ mol −1
Thermal conductivity 12 W m −1 K −1
Chemically
Oxidation states 3
Normal potential −2.13 V
(Ac 3+ + 3 e - → Ac)
Electronegativity 1.1 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP
224 Ac {syn.} 2.9 h ε 1.403 224 ra
α 9,100 220 Fr
β - 0.232 224 Th
225 Ac {syn.} 10 d α 5.935 221 Fr
226 Ac {syn.} 29.4 h β - 0.640 226 Th
ε 1.116 226 Ra
α 5.536 222 Fr
227 Ac 100% 21,773 a β - 0.045 227 Th
α 5.536 223 Fr
228 Ac in traces 6.15 h β - 2.127 228 Th
For other isotopes see list of isotopes
Hazard and safety information

GHS hazard labeling
no classification available
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions .

Actinium is a radioactive chemical element with the element symbol Ac and the atomic number 89. In the periodic table of the elements it is in the 3rd  IUPAC group , the scandium group . The element is a metal and belongs to the 7th period , d-block . It is the namesake of the group of actinides , the 14 elements that follow it.

## history

Mendeleev's periodic table from 1871 with a gap for actinium at the bottom, in front of thorium ( Th = 231 )

Actinium was discovered in 1899 by the French chemist André-Louis Debierne , who isolated it from pitchblende and initially attributed similarities to titanium or thorium ; He derived his name from the Greek ἀκτίς aktís 'beam' because of the radioactivity . Friedrich Giesel discovered the element independently in 1902 and described a similarity to lanthanum ; he gave it the name Emanium , a formation from the Latin emano “ to flow out”, also with reference to the emitted radiation. After Actinium and Emanium were recognized as identical in 1904, Debierne's naming was given preference since he first discovered it.

The history of the discovery was still described as questionable in publications from 1971 and later in 2000. They show that the publications of 1904 on the one hand and those of 1899 and 1900 on the other hand show contradictions.

## Extraction and presentation

Since there is little actinium in uranium ores , this source does not play a role in extraction. Technically, the isotope 227 Ac is produced by irradiating 226 Ra with neutrons in nuclear reactors .

${\ displaystyle \ mathrm {^ {226} _ {\ 88} Ra \ + \ _ {0} ^ {1} n \ \ longrightarrow \ _ {\ 88} ^ {227} Ra \ {\ xrightarrow [{42, 2 \ min}] {\ beta ^ {-}}} \ _ {\ 89} ^ {227} Ac}}$
The times given are half-lives .

Due to the rapid decay of actinium, only small amounts were always available. The first man-made production of actinium was carried out at the Argonne National Laboratory in Chicago .

## properties

### Physical Properties

The metal is shiny silver-white and relatively soft. Due to its strong radioactivity, Actinium glows in a light blue light in the dark.

Actinium is the eponymous element of the actinides , similar to lanthanum for the lanthanoids . The group of elements shows more distinct differences than the lanthanoids; therefore it was not until 1945 that Glenn T. Seaborg was able to suggest the most important changes to Mendeleev's periodic table: the introduction of actinides.

### Chemical properties

It is very reactive and can be attacked by air and water, but is covered with a layer of actinium oxide, which protects it from further oxidation. The Ac 3+ ion is colorless. Actinium's chemical behavior is very similar to that of lanthanum . Actinium is trivalent in all ten known compounds.

## Isotopes

26 isotopes are known , only two of which occur naturally. The longest-lived isotope 227 Ac ( half-life 21.8 years) has two decay channels : it is an alpha and a beta emitter . 227 Ac is a decay product of the uranium isotope 235 U and occurs to a small extent in uranium ores. From this a weighable amount of 227 Ac can be obtained, which thus enables a relatively simple study of this element. Since there are some gamma emitters among the radioactive decay products , complex radiation protection precautions are necessary.

## use

Actinium is used to generate neutrons, which play a role in activation analyzes. It is also used for thermionic energy conversion .

During the dual decay of 227 Ac, the largest part goes into the thorium isotope 227 Th with emission of beta particles , but approx. 1% decays through alpha emission to Francium 223 Fr. A solution of 227 Ac is therefore a source for the short-lived 223 Fr can be used. The latter can then be separated and examined regularly.

## safety instructions

Classifications according to the CLP regulation are not available because they only include chemical hazard and play a completely subordinate role compared to the hazards based on radioactivity . The latter also only applies if the amount of substance involved is relevant.

Only a small number of actinium compounds are known. With the exception of AcPO 4 , they are all similar to the corresponding lanthanum compounds and contain actinium in the +3 oxidation state. In particular, the lattice constants of the respective lanthanum and actinium compounds differ only in a few percent.

formula colour symmetry Space group Pearson symbol a (pm) b (pm) c (pm) Z Density,
g / cm 3
Ac silver fcc Fm 3 m (No. 225) cF4 531.1 531.1 531.1 4th 10.07
AcH 2 cubic Fm 3 m (No. 225) cF12 567 567 567 4th 8.35
Ac 2 O 3 White trigonal P 3 m 1 (No. 164) hP5 408 408 630 1 9.18
Ac 2 S 3 cubic I 4 3 d (No. 220) cI28 778.56 778.56 778.56 4th 6.71
AcF 3 White hexagonal P 3 c 1 (No. 165) hP24 741 741 755 6th 7.88
AcCl 3 hexagonal P 6 3 / m (No. 176) hP8 764 764 456 2 4.8
AcBr 3 White hexagonal P 6 3 / m (No. 176) hP8 764 764 456 2 5.85
AcOF White cubic Fm 3 m (No. 225) 593.1 8.28
AcOCl tetragonal 424 424 707 7.23
AcOBr tetragonal 427 427 740 7.89
AcPO 4 • 0.5H 2 O hexagonal 721 721 664 5.48

### Oxides

Actinium (III) oxide  (Ac 2 O 3 ) can be obtained by heating the hydroxide at 500 ° C or the oxalate at 1100 ° C in vacuo. The crystal lattice is isotypic with the oxides of most trivalent rare earth metals .

### Halides

Actinium (III) fluoride  (AcF 3 ) can be prepared either in solution or by solid reaction. In the first case, hydrofluoric acid is added to an Ac 3+ solution at room temperature and the product is precipitated. in the other case actinium metal is treated with hydrogen fluoride at 700 ° C in a platinum apparatus.

Actinium (III) chloride  (AcCl 3 ) is obtained by reacting actinium hydroxide or oxalate with carbon tetrachloride at temperatures above 960 ° C.

The reaction of aluminum bromide and actinium (III) oxide leads to actinium (III) bromide  (AcBr 3 ) and treatment with moist ammonia at 500 ° C leads to the oxibromide AcOBr.

### More connections

If sodium dihydrogen phosphate  (NaH 2 PO 4 ) is added to a solution of actinium in hydrochloric acid, white-colored actinium phosphate  (AcPO 4  · 0.5 H 2 O) is obtained; Heating actinium (III) oxalate with hydrogen sulfide at 1400 ° C for a few minutes results in black actinium (III) sulfide  (Ac 2 S 3 ).

## literature

Wiktionary: Actinium  - explanations of meanings, word origins, synonyms, translations
Commons : Actinium  - collection of images, videos and audio files

## Individual evidence

1. ^ Harry H. Binder: Lexicon of the chemical elements , S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 .
2. The values ​​for the properties (info box) are taken from www.webelements.com (Actinium) , unless otherwise stated .
3. entry on actinium in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( https://physics.nist.gov/asd ). Retrieved June 13, 2020.
4. entry on actinium at WebElements, https://www.webelements.com , accessed on June 13, 2020.
5. The hazards emanating from radioactivity do not belong to the properties to be classified according to the GHS labeling. With regard to other hazards, this element has either not yet been classified or a reliable and citable source has not yet been found.
6. ^ André-Louis Debierne: "Sur une nouvelle matière radio-active", in: Comptes rendus , 1899 , 129 , pp. 593-595 ( digitized on Gallica ).
7. ^ André-Louis Debierne: "Sur un nouvel élément radio-actif: l'actinium", in: Comptes rendus , 1900 , 130 , pp. 906-908 ( digitized on Gallica ).
8. a b N. A. Figurowski, The discovery of the chemical elements and the origin of their names , in German translation by Leo Korniljew / Ernst Lemke, Moscow 1981, ISBN 3-7614-0561-8 , p. 64.
9. ^ Friedrich Oskar Giesel: "About radium and radioactive substances", in: Reports of the German Chemical Society , 1902 , 35  (3), pp. 3608-3611 ( doi: 10.1002 / cber.190203503187 ).
10. Friedrich Oskar Giesel: "Ueber den Emanationskörper (Emanium)", in: Reports of the German Chemical Society , 1904 , 37  (2), pp. 1696-1699 ( doi: 10.1002 / cber.19040370280 ).
11. Friedrich Oskar Giesel: "Ueber Emanium", in: Reports of the German Chemical Society , 1905 , 38  (1), pp. 775-778 ( doi: 10.1002 / cber.190503801130 ).
12. HW Kirby: "The Discovery of Actinium", in: Isis , 1971 , 62  (3), pp. 290-308 ( JSTOR 229943 ).
13. ^ JP Adloff: "The centenary of a controversial discovery: actinium", in: Radiochim. Acta , 2000 , 88 , p. 123 ( doi: 10.1524 / ract.2000.88.3-4.123 ).
14. a b c d Joseph G. Stites, Murrell L. Salutsky, Bob D. Stone: "Preparation of Actinium Metal", in: J. Am. Chem. Soc. , 1955 , 77  (1), pp. 237-240 ( doi: 10.1021 / ja01606a085 ).
15. Frederick Seitz, David Turnbull: Solid state physics: advances in research and applications , Academic Press, 1964, ISBN 0-12-607716-9 , pp. 289-291 ( limited preview in the Google book search).
16. Glenn T. Seaborg: "The Transuranium Elements", in: Science , 1946 , 104 , No. 2704, pp. 379-386 ( doi: 10.1126 / science.104.2704.379 ; PMID 17842184 ).
17. ^ JJ Katz, WM Manning: “Chemistry of the Actinide Elements”, in: Annual Review of Nuclear Science , 1952 , 1 , pp. 245-262 ( doi: 10.1146 / annurev.ns.01.120152.001333 ).
18. Sherman Fried, French Hagemann, WH Zachariasen: “The Preparation and Identification of Some Pure Actinium Compounds”, in: J. Am. Chem. Soc. , 1950 , 72 , pp. 771-775 ( doi: 10.1021 / ja01158a034 ).
19. a b J. D. Farr, AL Giorgi, MG Bowman, RK Money: "The crystal structure of actinium metal and actinium hydride", in: Journal of Inorganic and Nuclear Chemistry , 1961 , 18 , pp. 42-47 ( doi: 10.1016 / 0022-1902 (61) 80369-2 ).
20. ^ A b W. H. Zachariasen: "Crystal Chemical Studies of the 5 f Series of Elements. XII. New Compounds Representing Known Structure Types ", in: Acta Crystallographica , 1949 , 2 , pp. 388-390 ( doi: 10.1107 / S0365110X49001016 ).
21. ^ WH Zachariasen: "Crystal Chemical Studies of the 5 f Series of Elements. VI. The Ce 2 S 3 - Ce 3 S 4 Type of Structure ", in: Acta Crystallographica , 1949 , 2 , pp. 57-60 ( doi: 10.1107 / S0365110X49000126 ).
22. ^ Gerd Meyer, Lester R. Morss: Synthesis of lanthanide and actinide compounds , Springer, 1991, ISBN 0-7923-1018-7 , p. 71 ( limited preview in Google book search).
23. ^ A b W. H. Zachariasen: "Crystal Chemical Studies of the 5 f Series of Elements. I. New Structure Types ", in: Acta Crystallographica , 1948 , 1 , pp. 265-268 ( doi: 10.1107 / S0365110X48000703 ).
24. Gerd Meyer, Lester R. Morss: Synthesis of lanthanide and actinide compounds , Springer, 1991, ISBN 0-7923-1018-7 , pp. 87-88 ( limited preview in Google book search).