Astatine (Environmental & Earth Science)
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| Physical Properties | ||
|---|---|---|
| Color | --- | |
| Phase at Room Temp. | solid | |
| Density (g/cm3) | --- | |
| Hardness (Mohs) | --- | |
|
Melting Point (K) |
575.2 | |
|
Boiling Point (K) |
--- | |
| Heat of Fusion (kJ/mol) | --- | |
| Heat of Vaporization (kJ/mol) | --- | |
| Heat of Atomization (kJ/mol) | 92 | |
| Thermal Conductivity (J/m sec K) | --- | |
| Electrical Conductivity (1/mohm cm) | --- | |
| Source | Synthetic (Th or U decay) | |
| Atomic Properties | ||
| Electron Configuration | [Xe]6s24f145d106p5 | |
|
Number of Isotopes |
42 (0 natural) | |
| Electron Affinity (kJ/mol) | 270 | |
| First Ionization Energy (kJ/mol) | 890 | |
| Second Ionization Energy (kJ/mol) | --- | |
| Third Ionization Energy (kJ/mol) | --- | |
| Electronegativity | 2.2 | |
| Polarizability (Å3) | 6.0 | |
| Atomic Weight | 210 | |
| Atomic Volume (cm3/mol) | --- | |
| Ionic Radius2- (pm) | --- | |
| Ionic Radius1- (pm) | --- | |
| Atomic Radius (pm) | --- | |
| Ionic Radius1+ (pm) | --- | |
| Ionic Radius2+ (pm) | --- | |
| Ionic Radius3+ (pm) | --- | |
| Common Oxidation Numbers | -1, +1 | |
| Other Oxid. Numbers | +3, +5, +7 | |
| Abundance | ||
| In Earth's Crust (mg/kg) | --- | |
| In Earth's Ocean (mg/L) | --- | |
| In Human Body (%) | 0% | |
| Regulatory / Health | ||
| CAS Number | 7440-68-8 | |
| OSHA Permissible Exposure Limit | No limits | |
| OSHA PEL Vacated 1989 | No limits | |
|
NIOSH Recommended Exposure Limit |
No limits | |
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Sources: |
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Astatine is a synthetically produced radioactive element designated the atomic symbol At and atomic number 85. Astatine derives its name from the greek word astatos which means unstable.
It was first synthesized in 1940 by D.R. Corson, K.R. MacKenzie, and E. Segre at the University of California. Corson and his colleagues essentially bombarded bismuth-209 with alpha particles, which produced astatine-211 as well as neutrons:
209Bi + He2+ ? 211At + 21n
Three years after it was first synthesized in a lab, trace amounts of astatine were discovered in some natural occurrences of luranium and thorium minerals. Naturally occurring astatine is considered the rarest element to be found in the Earth's crust. Its rarity is a consequence of the element's short half life.
Properties
Astatine is a non metallic element that exists at room temperature in a solid state. It is the heaviest element of the halogen group (group 17). The other halogens, from lowest to highest atomic weight, are: fluorine, chlorine, bromine and iodine.
The word halogen is ultimately derived from the Greek words for salt, hals and the root word gen-, meaning to generate, hence generators of salt. The halogens are extremely reactive substances. When a halogen comes in contact with hydrogen, an acidic compound is formed, which then can beconverted into a salt.
Astatine is a highly radioactive element. All of its known isotopes (around 20) are radioactive. Its most stable isotopes 210At and 211At have half-lives of 8.1 hours and 7.2 hours respectively.
Applications
Astatine can be used to treat certain thyroid conditions. Radio-iodine (iodine-131) is more commonly or more widely used than astatine. However, astatine has some advantages over iodine, because, while it is similar to iodine in terms of chemical properties, astatine emits alpha particles, which are energetically stronger and travel shorter distances than the beta particles emitted by iodine-131. Because of this, astatine can be more effective in treating thyroid problems such as cancer while not affecting other nearby glands.
Other than the potential of it being used to treat thyroid cancer, astatine has no other known uses becauseof itsshort half-life.
Further reading
- Takahashi, N; Yano, D; Baba, H (1992). "Chemical behavior of astatine molecules". Proceedings of the international conference on evolution in beam applications, Takasaki, Japan, Nov 5‒8, 1991. pp.536‒539..
- Meyers, Robert Allen (2001). "Halogen chemistry". Encyclopedia of physical science and technology (3rd ed.). Academic Press. pp.197–222 (202). ISBN978-0-12-227410-7.
- Astatine Reading Materials
