| Discovery date | 1940 |
| Discovered by |
Dale R. Corson, Kenneth Ross MacKenzie, Emilio Segrè
|
| Origin of the name | The name comes from the Greek 'astatos', meaning unstable. |
| Allotropes |
|
At
Astatine
85
[210]
| Group | 17 | Melting point | 300°C, 572°F, 573 K |
| Period | 6 | Boiling point | 350°C, 662°F, 623 K |
| Block | p | Density (g cm−3) | Unknown |
| Atomic number | 85 | Relative atomic mass | [210] |
| State at 20°C | Solid | Key isotopes | 210At, 211At |
| Electron configuration | [Xe] 4f145d106s26p5 | CAS number | 7440-68-8 |
| ChemSpider ID | 4573995 | ChemSpider is a free chemical structure database | |
Image explanation
The image is based around the familiar radiation hazard symbol and reflects the unstable and reactive nature of the element.
Appearance
Astatine is a dangerously radioactive element.
Uses
There are currently no uses for astatine outside of research. The half-life of the most stable isotope is only 8 hours, and only tiny amounts have ever been produced.
A mass spectrometer has been used to confirm that astatine behaves chemically like other halogens, particularly iodine.
Biological role
Astatine has no known biological role. It is toxic due to its radioactivity.
Natural abundance
Astatine can be obtained in a variety of ways, but not in weighable amounts. Astatine-211 is made in nuclear reactors by the neutron bombardment of bismuth-200.
In 1939, two groups came near to discovering this element in mineral samples. Horia Hulubei and Yvette Cauchois analysed mineral samples using a high-resolution X-ray apparatus and thought they had detected it. Meanwhile, Walter Minder observed the radioactivity of radium and said it appeared have another element present. He undertook chemical tests which suggested it was like iodine.
Element 85 was convincingly produced for the first time at the University of California in 1940 by Dale R. Corson, K.R. Mackenzie, and Emilio Segré. Their astatine was made by bombarding bismuth with alpha particles. Although they reported their discovery, they were unable to carry on with their research due to World War II and the demands of the Manhattan project which diverted all researchers of radioactive materials towards the making of nuclear weapons.
| Atomic radius, non-bonded (Å) | 2.02 | Covalent radius (Å) | 1.48 |
| Electron affinity (kJ mol−1) | 270.2 |
Electronegativity (Pauling scale) |
2.2 |
|
Ionisation energies (kJ mol−1) |
1st
-
2nd
-
3rd
-
4th
-
5th
-
6th
-
7th
-
8th
-
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| Common oxidation states | 7, 5, 3, 1, -1 | ||||
| Isotopes | Isotope | Atomic mass | Natural abundance (%) | Half life | Mode of decay |
| 210At | 209.987 | - | 8.1 h | EC | |
| - | α | ||||
| 211At | 210.987 | - | 7.21 h | EC | |
| - | α | ||||
|
Specific heat capacity (J kg−1 K−1) |
Unknown | Young's modulus (GPa) | Unknown | |||||||||||
| Shear modulus (GPa) | Unknown | Bulk modulus (GPa) | Unknown | |||||||||||
| Vapour pressure | ||||||||||||||
| Temperature (K) |
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| Pressure (Pa) |
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| Listen to Astatine Podcast |
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Transcript :
Chemistry in its element: astatine(Promo) You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry. (End promo) Chris Smith Hello, a record breaker is the star of the show this week as we meet the chemical whose name means unstable and which is in the famous Guinness book as the world's rarest elements, but some bright medical future turn this rarity into something in common use. The element is astatine and to tell the story here is Mark Peplow. Mark Peplow You can learn a lot about someone by meeting their family and the same is true for the element. That's how we come to know so much about astatine. Often trumpeted as the rarest naturally occurring element in the world, it's only by extrapolating the properties of the other members of the halogen family, fluorine, chlorine, bromine and iodine the scientists could even begin to look at their obese sibling. Astatine was the second synthetic element to be conclusively identified just three years after technetium, was isolated by Carlo Perrier and Emilio Segre of the University of Palermo. The element had actually been created in a cyclotron particle accelerator at the University of California in Berkeley where Segre spent the following summer continuing his research. But miles away from Italy Mussolini's government passed anti Semitic laws which barred Jewish people like Segre from holding University positions; so he stayed where he was, taking up a job at Berkeley and in 1940 he helped to discover astatine along with Dale Corson, he was then a post doc and later went on to become President of Cornell University and grant student Kenneth MacKenzie. They bombarded a sheet of bismuth metal, that's two doors down from astatine in the periodic table, with alpha particle to produce astatine-211, which has a half life of about 71/2 hours and it neatly filled the gap in the periodic table just beneath iodine. Segre went on to become a group leader for the Manhattan project which built the first atomic weapon. And it was only once the Second World War was over that the trio proposed the name Astatine for their elemental discovery. It was from the Greek word meaning unstable. Astatine is actually found in nature although it only appears as a minor spur on an obscure pathway in uranium fission. According to Greenwood and Earshaw, the Bible of inorganic chemistry, it's been estimated that the top kilometre of the earth's crust contains less than 50 mg of astatine making a Guinness world record's rarest element. Astatine is the least reactive of the halogens but just like the rest of them it combines with hydrogen to make hydrogen astatide which dissolves in water to make hydroastatic acid; it is just like a weaker version of hydrochloric acid. If you could ever isolate enough of this stuff astatine would be an even darker purple solid than iodine. Overall there are more than 30 isotopes of the element, all radioactive with the longest lived having a half life of just 8 hours. You might think that something so rare would be completely useless, but perhaps not. Several groups of scientists believe that astatine-211 could be used to treat certain types of cancer. Radioactive Iodine 131 is already used to treat Thyroid cancers for example, because it preferentially accumulates in that organ. This concentrates the dose of radiation and it reduces the exposure of healthy tissue. The trouble is that Iodine 131 like many other therapeutic radioisotopes emit beta particles, fast moving electrons which can penetrate through a few millimetres of tissue. That makes them ideal for tackling substantial solid tumours, but not for the small clusters of cells, because the energy from radioactive decay is spread far outside the boundary of the tumour. Another form of radioactive decay, alpha particles would be much more suitable because these bulky clusters of 2 protons and 2 neutrons, effectively helium nucleus, can only travel about 50 micrometers in tissue. Astatine-211 is not only an alpha emitter, it has also got a very short half life and the fact that it decays to a stable non-radioactive isotope of lead means that the radiation dose is quite brief. It even has a secondary decay pathway that creates a few x-rays which doctors could use to track exactly where the isotope is in the body. The key challenge is though to connect the radioactive astatine atoms to a molecule that will seek out specific cancer cells; then to the chemistry as soon as possible before the radioactivity decays away and to make sure that the astatine doesn't fall off its targeted molecule once it is injected into the body. This may of course take decades of research to achieve but chemists have already identified rapid ways to make these astatine complexes and there has even been a small but very promising clinical trial at Duke University in North Carolina, testing astatine radiotherapy in 18 brain tumour patients. So if astatine does become a successful medicine there's every chance that the rarest element might become surprisingly common. Chris Smith Mark Peplow, telling the tale of the world's rarest element. Well from rare to lethal now and especially if you're a monk. Phillip Ball Valentine admitted that antimony was poisonous. In fact he offered an apocryphal explanation for the name, saying that it derives from anti-monachos, meaning anti-monk in Latin because he once unintentionally poisoned several of his fellow monks by adding it secretly to their food in an attempt to improve their health. Chris Smith Phil Ball who will be bringing antimony to life for us in next week's Chemistry in its element. I'm Chris Smith, thank you for listening. See you next time. (Promo) Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists.com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld.org/elements. (End promo)
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Visual Elements images and videos
© Murray Robertson 1998-2017.
W. M. Haynes, ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca Raton, FL, 95th Edition, Internet Version 2015, accessed December 2014.
Tables of Physical & Chemical Constants, Kaye & Laby Online, 16th edition, 1995. Version 1.0 (2005), accessed December 2014.
J. S. Coursey, D. J. Schwab, J. J. Tsai, and R. A. Dragoset, Atomic Weights and Isotopic Compositions (version 4.1), 2015, National Institute of Standards and Technology, Gaithersburg, MD, accessed November 2016.
T. L. Cottrell, The Strengths of Chemical Bonds, Butterworth, London, 1954.
John Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, New York, 2nd Edition, 2011.
Thomas Jefferson National Accelerator Facility - Office of Science Education, It’s Elemental - The Periodic Table of Elements, accessed December 2014.
Periodic Table of Videos, accessed December 2014.
Derived in part from material provided by the British Geological Survey © NERC.
Elements 1-112, 114, 116 and 117 © John Emsley 2012. Elements 113, 115, 117 and 118 © Royal Society of Chemistry 2017.
Produced by The Naked Scientists.
Created by video journalist Brady Haran working with chemists at The University of Nottingham.
© Murray Robertson 1998-2017.
Data
W. M. Haynes, ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca Raton, FL, 95th Edition, Internet Version 2015, accessed December 2014.
Tables of Physical & Chemical Constants, Kaye & Laby Online, 16th edition, 1995. Version 1.0 (2005), accessed December 2014.
J. S. Coursey, D. J. Schwab, J. J. Tsai, and R. A. Dragoset, Atomic Weights and Isotopic Compositions (version 4.1), 2015, National Institute of Standards and Technology, Gaithersburg, MD, accessed November 2016.
T. L. Cottrell, The Strengths of Chemical Bonds, Butterworth, London, 1954.
Uses and properties
John Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, New York, 2nd Edition, 2011.
Thomas Jefferson National Accelerator Facility - Office of Science Education, It’s Elemental - The Periodic Table of Elements, accessed December 2014.
Periodic Table of Videos, accessed December 2014.
Supply risk data
Derived in part from material provided by the British Geological Survey © NERC.
History text
Elements 1-112, 114, 116 and 117 © John Emsley 2012. Elements 113, 115, 117 and 118 © Royal Society of Chemistry 2017.
Podcasts
Produced by The Naked Scientists.
Periodic Table of Videos
Created by video journalist Brady Haran working with chemists at The University of Nottingham.
