Astatine is a radioactive chemical element with an atomic number 85 in the periodic table of elements. The total amount of astatine found naturally in the Earth’s crust is almost 25 grams at any given time, which makes astatine the rarest chemical element on Earth. Being a member of the family of halogen elements in the periodic table, the outer shell of astatine comprises seven valence electrons.
Chemical and Physical Properties of Astatine
The symbol in the periodic table of elements:
Atomic number: 85
Atomic weight (mass): 209.9871 [210 – average]
Group number: 17
Color: A shiny dark-colored chemical element
Physical state: Solid metal at room temperature
Electronegativity according to Pauling: 2.2
Density: No data available
Melting point: 302°C
Boiling point: 337°C (estimation)
Van der Waals radius: 200 pm
Most characteristic isotopes: 210At, 211At
The energy of the first ionization:
The energy of the second ionization:
Discovery date: In 1940 by D.R.Corson, K.R. MacKenzie, E.Segré.
With the periodic table symbol At, the atomic mass of 209.9871 g.mol -1, and electronic configuration [Xe] 4f145d106s26p5, аstatine reaches its (estimated) boiling point at 337°C with probable valences of 1, 3, 5, or 7, while the melting point is achieved at 302°C. Both melting and boiling points of astatine increase with the atomic number. This member of the halogen family of elements in the periodic table has an electronegativity of 2.2, according to Pauling, whereas the atomic radius according to van der Waals is 200 pm.
The chemical properties of astatine also include:
- plating of astatine onto a cathode;
- forming a stable monatomic cation in aqueous solution;
- co-precipitating of astatine with metal sulfides in hydrochloric acid.
How Was Astatine Discovered?
The story of astatine begins in 1869 when the Russian chemist Dmitri Mendeleev managed to determine the properties of a chemical element with an atomic number 85 that was yet to be named. The first choice for the name of the radioactive metal was eka-iodine, due to the fact that it was placed under iodine (I) – a member of the halogen family of elements in the periodic table.
The Romanian physicist Horia Hulubei and the French physicist Yvette Cauchois believed that they had discovered element 85 via X-ray analysis. Their efforts were disregarded by the Austrian chemist Friedrich Paneth in 1947.
However, in 1939, there was information that this particular element was independently discovered by the Alabama Polytechnic Institute researcher, Fred Allison, who opted for the name “alabamine” in an attempt to label the newly discovered chemical element. Unfortunately, due to his dysfunctional equipment, the resulting formulae could not be used by the other researchers. In the meantime, World War II disrupted any further research on the heaviest halogen element in the periodic table.
In 1940, three researchers at the University of California, Berkeley (Dale R. Corson, Kenneth Ross Mackenzie, and Emilio Segrè) managed to resume the research and artificially produce astatine by bombarding bismuth-209 with alpha particles in a cyclotron particle accelerator, since this highly radioactive and unstable element could not be found in nature. Astatine-211 and two free neutrons were produced as a result of this chemical reaction triggered by the aforementioned University of California researchers.
How Did Astatine Get Its Name?
The name of this radioactive chemical element comes from the Greek word “astatos” (“αστατος”). This Greek word carries the meaning of ‘unstable’ which resembles the nature of astatine. The chemical properties of astatine were defined by the scientists from the Jefferson Laboratory.
Where Can You Find Astatine?
Astatine is a man-made chemical element, i.e. it cannot be found abundantly in nature. This radioactive metal is produced by bombarding a bismuth target (bismuth-209 isotope) with alpha particles producing At-209, At-210, and At-211.
This radioactive chemical element with the highest weight among the halogen elements can be also traced in the following radioactive decay series: natural astatine-218 in the uranium series, astatine-216 in the thorium series, and astatine-215 as well as astatine-219 in the actinium series.
Astatine in Everyday Life
The Use of Astatine in Nuclear Medicine
This artificially radioactive element is applied in medicine as a radioisotope for the treatment of malignant tumors and cancer. The widespread use of astatine is due to the astatine-211 isotope. Namely, it’s applied for targeted alpha-particle therapy (radiotherapy).
How Dangerous Is Astatine?
The extremely small amount of At-215, At-218, and At-219 that can be traced in nature results from the decay of uranium and thorium. Since astatine is not naturally found in significant amounts and has a very short half-life of 8.1 hours or less, it does not present a significant health hazard. However, this man-made radioactive element can display the negative side of its radioactive properties if handled without care in the research labs or medical institutes. High exposure to astatine can lead to astatine bioaccumulation in the thyroid gland.
Astatine does not have any natural isotopes. The list of known isotopes contains 39 radioactive isotopes, with mass numbers from 191 to 229. According to the Jefferson Laboratory, the number of the longest-lived isotope among them is astatine-210 (210At). At the same time, this is also the most stable isotope of this radioactive element of the periodic table.
The following is a tabular representation of astatine isotopes:
|Z||N||Isotopic mass (Da)
[n 2][n 3]
[n 5][n 6]
|Excitation energy[n 6]|
|192At||85||107||192.00314(28)||11.5(0.6) ms||α (99.79%)||188Bi||3+#|
|β+, SF (0.21%)||(various)|
|192mAt||330(90)# keV||88(6) ms||α (99.79%)||188mBi||(9-, 10−)|
|β+, SF (0.21%)||(various)|
|193m1At||50 keV||21(5) ms||(7/2−)|
|193m2At||39 keV||27(+4−5) ms||(13/2+)|
|194At||85||109||193.99873(20)||286(7) ms||α||190Bi||(4-, 5-)|
|194mAt||480(190) keV||323(7) ms||α||190Bi||(9-, 10-)|
|195At||85||110||194.996268(10)||328(20) ms||α (75%)||191Bi||(1/2+)|
|195mAt||34(7) keV||147(5) ms||(7/2-)|
|196At||85||111||195.99579(6)||253(9) ms||α (96%)||192Bi||(3+)|
|196m1At||−30(80) keV||20# ms||(10−)|
|196m2At||157.9(1) keV||11 µs||(5+)|
|197At||85||112||196.99319(5)||0.390(16) s||α (96%)||193Bi||(9/2−)|
|197mAt||52(10) keV||2.0(2) s||(1/2+)|
|198At||85||113||197.99284(5)||4.2(3) s||α (94%)||194Bi||(3+)|
|198mAt||330(90)# keV||1.0(2) s||(10−)|
|199At||85||114||198.99053(5)||6.92(13) s||α (89%)||195Bi||(9/2−)|
|200At||85||115||199.990351(26)||43.2(9) s||α (57%)||196Bi||(3+)|
|200m1At||112.7(30) keV||47(1) s||α (43%)||196Bi||(7+)|
|200m2At||344(3) keV||3.5(2) s||(10−)|
|201At||85||116||200.988417(9)||85(3) s||α (71%)||197Bi||(9/2−)|
|202At||85||117||201.98863(3)||184(1) s||β+ (88%)||202Po||(2, 3)+|
|202m1At||190(40) keV||182(2) s||(7+)|
|202m2At||580(40) keV||460(50) ms||(10−)|
|203At||85||118||202.986942(13)||7.37(13) min||β+ (69%)||203Po||9/2−|
|204At||85||119||203.987251(26)||9.2(2) min||β+ (96%)||204Po||7+|
|204mAt||587.30(20) keV||108(10) ms||IT||204At||(10−)|
|205At||85||120||204.986074(16)||26.2(5) min||β+ (90%)||205Po||9/2−|
|205mAt||2339.65(23) keV||7.76(14) µs||29/2+|
|206At||85||121||205.986667(22)||30.6(13) min||β+ (99.11%)||206Po||(5)+|
|206mAt||807(3) keV||410(80) ns||(10)−|
|207At||85||122||206.985784(23)||1.80(4) h||β+ (91%)||207Po||9/2−|
|208At||85||123||207.986590(28)||1.63(3) h||β+ (99.5%)||208Po||6+|
|209At||85||124||208.986173(8)||5.41(5) h||β+ (96%)||209Po||9/2−|
|210At||85||125||209.987148(8)||8.1(4) h||β+ (99.8%)||210Po||(5)+|
|210m1At||2549.6(2) keV||482(6) µs||(15)−|
|210m2At||4027.7(2) keV||5.66(7) µs||(19)+|
|211At||85||126||210.9874963(30)||7.214(7) h||EC (58.2%)||211Po||9/2−|
|212At||85||127||211.990745(8)||0.314(2) s||α (99.95%)||208Bi||(1−)|
|212m1At||223(7) keV||0.119(3) s||α (99%)||208Bi||(9−)|
|212m2At||4771.6(11) keV||152(5) µs||(25−)|
|214m1At||59(9) keV||265(30) ns|
|214m2At||231(6) keV||760(15) ns||9−|
|215At||85||130||214.998653(7)||0.10(2) ms||α||211Bi||9/2−||Trace[n 7]|
|216At||85||131||216.002423(4)||0.30(3) ms||α (99.99%)||212Bi||1−|
|216mAt||413(5) keV||100# µs||(9−)|
|217At||85||132||217.004719(5)||32.3(4) ms||α (99.98%)||213Bi||9/2−||Trace[n 8]|
|218At||85||133||218.008694(12)||1.5(3) s||α (99.9%)||214Bi||1−#||Trace[n 9]|
|219At||85||134||219.011162(4)||56(3) s||α (97%)||215Bi||(9/2-)||Trace[n 7]|
|220At||85||135||220.01541(6)||3.71(4) min||β− (92%)||220Rn||3(−#)|
Alpha Decay of Astatine Isotopes
The short half-life of astatine makes this highly radioactive chemical element decay into bismuth, radon, polonium, or other isotopes of astatine. When the mass of the astatine nucleus increases, the high energies of alpha decay decrease, and vice versa.
The most stable astatine isotope (210At) decays into bismuth-206 through alpha decay or into polonium-210 through electron capture to polonium-211, which undergoes further alpha decay in the form of an extremely short-lived nuclide.
|Alpha decay characteristics for sample astatine isotopes[h]|
|207||−13.243 MeV||1.80 h||8.6%||20.9 h|
|208||−12.491 MeV||1.63 h||0.55%||12.3 d|
|209||−12.880 MeV||5.41 h||4.1%||5.5 d|
|210||−11.972 MeV||8.1 h||0.175%||193 d|
|211||−11.647 MeV||7.21 h||41.8%||17.2 h|
|212||−8.621 MeV||0.31 s||≈100%||0.31 s|
|213||−6.579 MeV||125 ns||100%||125 ns|
|214||−3.380 MeV||558 ns||100%||558 ns|
|219||10.397 MeV||56 s||97%||58 s|
|220||14.350 MeV||3.71 min||8%||46.4 min|
|221[i]||16.810 MeV||2.3 min||experimentally
Astatine forms compounds with the following elements or groups of elements: oxygen, sulfur, halides, selenium, palladium, nitrogen, lead, sodium, silver, and boron. Oxidation states of astatine range from −1 to +7 and are typically expressed with an odd number.
Hydrogen astatide (HAt) is created by a reaction of astatine with hydrogen, i.e. a weaker form of hydrochloric acid. The molecule of this compound is made of an astatine atom that forms two chemical bonds to a hydrogen atom. In this way, it becomes a hydrogen halide.
Astatides of silver, sodium, lead, palladium, and thallium, comprise some of the rare metal compounds of astatine.
The following is a list of some of the astatine compounds:
- Astatobenzene, C6H5At
- Hypochlorite, C6H5AtO2
- Astatine nitrate, [At(C5H5N)2]NO3
5 Interesting Facts and Explanations
- Dmitry Ivanovich Mendeleyev (January 27, 1834 – February 2, 1907) is the Russian chemist who created the periodic table of elements according to their similarity in electron configurations, as well as their chemical and physical properties.
- Hydrogen astatide (HAt) is also labeled as astatine hydride astatine, astido hydrogen or hydroastatic acid.
- The chemical element astatine has the strongest metallic properties among the other chemical elements from the halogen family in the periodic table.
- Astatine is concentrated in the thyroid gland of animals, just like iodine. In humans, it’s mainly concentrated in the lungs, spleen, and liver.
- The halogen family of elements consists of the following chemical elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts).