The chemical element astatine is classed as a halogen and a nonmetal. It was discovered in 1940 by Dale R. Coson, Kenneth Ross Mackenzie and Emilio Segrè.
|Classification:||Astatine is a halogen and a nonmetal|
|Color:||Presumed very dark|
|Atomic weight:||(210), no stable isotopes|
|Melting point:||302 oC, 575.2 K|
|Boiling point:||337 oC, 610 K|
|Neutrons in most abundant isotope:||125|
|Electron configuration:||[Xe] 4f14 5d10 6s2 6p5|
|Density @ 20oC:||7 g/cm3 approx.|
|Atomic volume:||30 cm3/mol approx.|
|Specific heat capacity||–|
|Heat of fusion||6 kJ mol-1 of I2|
|Heat of atomization||92 kJ mol-1|
|Heat of vaporization||40 kJ mol-1 of I2|
|1st ionization energy||890 kJ mol-1|
|2nd ionization energy||–|
|3rd ionization energy||–|
|Electron affinity||270 kJ mol-1|
|Minimum oxidation number||-1|
|Min. common oxidation no.||-1|
|Maximum oxidation number||7|
|Max. common oxidation no.||1|
|Electronegativity (Pauling Scale)||2.2|
|Polarizability volume||6 Å3|
|Reaction with air||–|
|Reaction with 15 M HNO3||–|
|Reaction with 6 M HCl||–|
|Reaction with 6 M NaOH||–|
|Ionic radius (1+ ion)||–|
|Ionic radius (2+ ion)||–|
|Ionic radius (3+ ion)||–|
|Ionic radius (1- ion)||–|
|Ionic radius (2- ion)||–|
|Ionic radius (3- ion)||–|
|Thermal conductivity||1.7 W m-1 K-1|
|Freezing/Melting point:||302 oC, 575.2 K|
Discovery of Astatine
The first periodic table, produced by Russian chemist Dmitri Mendeleev in 1869, had a space directly underneath iodine. The element to fill this space became known as eka-iodine. This alerted scientists to the possibility that if they looked, they could find the element that would fit into this space.
Many tried to find the new element in nature, but without success.
71 years after Mendeleev published his first periodic table, the element had still not been found, but was instead synthesized in the laboratory using one of the earliest particle accelerators.
Astatine was first produced in 1940 by Dale R. Coson, Kenneth Ross Mackenzie and Emilio Segrè at the University of California, Berkeley.
Segrè, working with Carlo Perrier, had previously synthesized technetium in 1937.(2), (3)
Astatine was made by bombarding bismuth-209 with alpha particles in a cyclotron (particle accelerator) to produce, after emission of two neutrons, astatine-211. The scientists found that the isotope they created was radioactive, so they named the element using the Greek ‘astatos’ meaning unstable.
It is now known that there are no stable astatine isotopes – the longest lived isotope, astatine-210, has a half-life of 8.3 hours. (3)
Three years later, astatine was found in nature by Berta Karlik and Traude Bernert as an intermediate in radioactive decay chains. Traces of the element appear naturally in uranium and thorium minerals as a decay product.
At any given time, about 25 grams of naturally occurring astatine exists on our planet. (3), (4)
Astatine’s Periodic Table Neighborhood
|Group 16||Group 17||Group 18|
Appearance and Characteristics
Astatine is highly radioactive and is only available in tiny quantities. Its properties are inferred from its position in the periodic table and by studying its chemistry in extremely dilute solutions.
Like the other halogens, astatine would be expected to form salts with metals such as sodium. Astatine can also react with hydrogen to form hydrogen astatide, which when dissolved in water, forms hydroastatic acid.
Astatine is the least chemically reactive of the halogens and exhibits the most metallic properties of the halogen group.
Uses of Astatine
Astatine-211 is sometimes used as a radioactive tracer and in cancer treatment.
Like iodine, it is known to accumulate in the thyroid gland.
Abundance and Isotopes
Abundance earth’s crust: About 25 grams exists in Earth’s crust at any given time.
Abundance solar system: negligible
Cost, pure: $ per 100g
Cost, bulk: $ per 100g
Source: Astatine is produced synthetically by bombarding bismuth with alpha particles. It can be obtained naturally from thorium or uranium decay.
Isotopes: More than 30 isotopes of astatine have been identified. All are very short-lived; astatine-210 has the longest half-life of 8 hours 10 minutes.
1. Image: Inductiveload
2. Gurdeep Raj, Advanced Inorganic Chemistry Vol-I, 1998, Krishna Prakashan Media, p344
3. Egon Wiberg, A.F. Holleman, Nils Wiberg, Inorganic Chemistry, 2001, Academic Press, p423
4. B.K. Sharma, Nuclear and Radiation Chemistry, 1997, Krishna Prakashan Media, p147
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