Dec 12 2012
Chemical Formula
At
Discovery
In 1940, three chemists named Dale R. Corson, Kenneth R. Mackenzie and Emilio Segre at the University of California found evidence for the existence of an unknown element at the end of whilst bombarding a bismuth isotope with alpha particles using a cyclotron. Through these experiments, they confirmed the existence of a new addition to the periodic table - Astatine-211.
Basic Information
| Name |
Astatine |
| Symbol |
At |
| Atomic number |
85 |
| Atomic weight |
210 amu |
| Standard state |
Solid at 298 K |
| CAS Registry ID |
7440-68-8 |
| Group in periodic table |
17 |
| Group name |
Halogen |
| Period in periodic table |
6 |
| Block in periodic table |
p-block |
| Color |
Metallic |
| Classification |
Semi-metallic |
| Melting point |
575 K (302°C or 576°F) |
| Boiling point |
613.15 K (~340°C or 644°F) |
| Density |
About 7g/cm3 |
| Phase at room temperature |
Solid |
Occurrence
Astatine can only be found on Earth following the decay of thorium and uranium. It is estimated that less than 30 g of astatine is present in the Earth's crust, only very few µg of astatine have been produced artificially so far, and elemental astatine has not been viewed by the naked eye due to its instability.
Isotopes
All 20 isotopes of astatine are radioactive. However, astatine-209, astatine-210, and astatine-211 have the longest half-lives of 5.5 to 8.3 hours.
Production
Astatine is formed by bombarding bismuth isotopes with alpha-particles. The resulting astatine is short-lived, with a half-life of just over 7 hours and hence it is necessary to prevent it from being evaporated by cooling the bismuth target during irradiation.
20983Bi + 42He → 11185At + 2 10n
The quantity of astatine thus obtained will be around 0.001mg.
Health Aspects
As astatine is available naturally in very minute quantities or produced artificially, there are no specific considerations with regards to the health effects of astatine. However, this element is evaluated in some of the nuclear research labs which require adoption of safety precautions and handling techniques. Furthermore Astatine, being a halogen, is said to accumulate in the thyroid region. The toxic effects of astatine are chemically similar to that of iodine.
Key Properties
The key properties of astatine are inferred from its periodic table position and through study conducted in diluted solutions as it breaks down quickly once produced or detected during experiments. Some of the inferred properties are given below:
- It is highly radioactive
- It holds almost all the metallic properties of the halogen groups
- It is heaviest halogen discovered so far
- It can react with hydrogen to produce hydrogen astatide.
Applications
Astatine can be very occasionally used as a radioactive tracer while treating cancer.
References