Periodic Table > Astatine
 

Terminology


Allotropes
Some elements exist in several different structural forms, these are called allotropes.


For more information on Murray Robertson’s image see Uses and properties facts below.

 

Fact box terminology


Group
Elements appear in columns or ‘groups’ in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.


Period
Elements are laid out into rows or ‘periods’ so that similar chemical behaviour is observed in columns.


Block
Elements are organised into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp, principal, diffuse, and fundamental.


Atomic Number
The number of protons in the nucleus.


Atomic Radius/non -bonded (Å)
based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties, for more details please refer to the CRC Handbook of Chemistry and Physics.


Electron Configuration
The arrangements of electrons above the last (closed shell) noble gas.


Isotopes
Elements are defined by the number of protons in its centre (nucleus), whilst the number of neutrons present can vary. The variations in the number of neutrons will create elements of different mass which are known as isotopes.


Melting Point (oC)
The temperature at which the solid-liquid phase change occurs.


Melting Point (K)
The temperature at which the solid-liquid phase change occurs.


Melting Point (oF)
The temperature at which the solid-liquid phase change occurs.


Boiling Point (oC)
The temperature at which the liquid-gas phase change occurs.


Boiling Point (K)
The temperature at which the liquid-gas phase change occurs.


Boiling Point (oF)
The temperature at which the liquid-gas phase change occurs.


Sublimation
Elements that do not possess a liquid phase at atmospheric pressure (1 atm) are described as going through a sublimation process.


Density (kgm-3)
Density is the weight of a substance that would fill 1 m3 (at 298 K unless otherwise stated).


Relative Atomic Mass
The mass of an atom relative to that of Carbon-12. This is approximately the sum of the number of protons and neutrons in the nucleus. Where more than one isotope exists the value given is the abundance weighted average.


Key Isotopes (% abundance)
An element must by definition have a fixed number of protons in its nucleus, and as such has a fixed atomic number, however variants of an element can exist with differing numbers of neutrons, and hence a different atomic masses (e.g. 12C has 6 protons and 6 neutrons and 13C has 6 protons and 7 neutrons).


CAS number
The Chemical Abstracts Service registry number is a unique identifier of a particular chemical, designed to prevent confusion arising from different languages and naming systems (where several isotopes exist, a value is presented for the most prevalent isotope).

Fact box

 
Group 17  Melting point 302 oC, 575.6 oF, 575.15 K 
Period Boiling point Unknown 
Block Density (kg m-3) Unknown 
Atomic number 85  Relative atomic mass 209.987  
State at room temperature Gas  Key isotopes 210At, 211At 
Electron configuration [Xe] 4f145d106s26p5  CAS number 7440-68-8 
ChemSpider ID 4573995 ChemSpider is a free chemical structure database
 

Uses and properties terminology


Image Explanation

Murray Robertson is the artist behind the images which make up Visual Elements. This is where the artist explains his interpretation of the element and the science behind the picture.


Natural Abundance

Where this element is most commonly found in nature.


Biological Roles

The elements role within the body of humans, animals and plants. Also functionality in medical advancements both today and years ago.


Appearance

The description of the element in its natural form.

Uses and properties

 
Image explanation
Imagery based around the familiar radiation hazard symbol and the unstable and reactive nature of the element.
Appearance
A dangerously radioactive element made in nuclear reactors. The half-life of the longer-lived isotope is only 8 hours.
Uses
The mass spectrometer has been used to confirm that this highly radioactive halogen 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 various ways, but not in weighable amounts. The usual method of preparation is neutron bombardment of 200Bi to produce 211At.
 
Atomic data terminology

Atomic radius/non -bonded (Å)
Based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties,for more details please refer to the CRC Handbook of Chemistry and Physics.


Electron affinity (kJ mol-1)
The energy released when an additional electron is attached to the neutral atom and a negative ion is formed (where several isotopes exist, a value is presented for the most prevalent isotope). *


Electronegativity (Pauling scale)
The degree to which an atom attracts electrons towards itself, expressed on a relative scale as a function bond dissociation energies, Ed in eV. χA - χB =(eV)-1/2sqrt(Ed(AB)-[Ed(AA)+Ed(BB)]/2), with χH set as 2.2 (where several isotopes exist, a value is presented for the most prevalent isotope).


1st Ionisation energy (kJ mol-1)
The minimum energy required to remove an electron from a neutral atom in its ground state (where several isotopes exist, a value is presented for the most prevalent isotope).


Covalent radius (Å)
The size of the atom within a covalent bond, given for typical oxidation number and coordination (where several isotopes exist, a value is presented for the most prevalent isotope). ***

Atomic data

 
Atomic radius, non-bonded (Å) 2.020 Covalent radius (Å) 1.48
Electron affinity (kJ mol-1) 270.159 Electronegativity
(Pauling scale)
2.200
Ionisation energies
(kJ mol-1)
 
1st
930.118
2nd
-
3rd
-
4th
-
5th
-
6th
-
7th
-
8th
-
 

Mining/Sourcing Information

Data for this section of the data page has been provided by the British Geological Survey. To review the full report please click here or please look at their website here.


Key for numbers generated


Governance indicators

1 (low) = 0 to 2

2 (medium-low) = 3 to 4

3 (medium) = 5 to 6

4 (medium-high) = 7 to 8

5 (high) = 9


Reserve base distribution

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %

(Where data are unavailable an arbitrary score of 2 was allocated. For example, Be, As, Na, S, In, Cl, Ca and Ge are allocated a score of 2 since reserve base information is unavailable. Reserve base data are also unavailable for coal; however, reserve data for 2008 are available from the Energy Information Administration (EIA).)


Production Concentration

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %


Crustal Abundance

1 (low) = 100 to 1000 ppm

2 (medium-low) =10 to 100 ppm

3 (medium) = 1 to 10 ppm

4 (medium-high) = 0.1 to 1 ppm

5 (high) = 0.1 ppm

(Where data are unavailable an arbitrary score of 2 was allocated. For example, He is allocated a score of 2 since crustal abundance data is unavailable.)


Explanations for terminology


Crustal Abundance (ppm)

The abundance of an element in the Earth's crust in parts-per-million (ppm) i.e. The number of atoms of this element per 1 million atoms of crust.


Sourced

The country with the largest reserve base.


Reserve Base Distribution

This is a measure of the spread of future supplies, recording the percentage of a known resource likely to be available in the intermediate future (reserve base) located in the top three countries.


Production Concentrations

This reports the percentage of an element produced in the top three countries. The higher the value, the larger risk there is to supply.


Total Governance Factor

The World Bank produces a global percentile rank of political stability. The scoring system is given below, and the values for all three production countries were summed.


Relative Supply Risk Index

The Crustal Abundance, Reserve Base Distribution, Production Concentration and Governance Factor scores are summed and then divided by 2, to provide an overall Relative Supply Risk Index.

Supply risk

 
Scarcity factor Unknown
Country with largest reserve base Unknown
Crustal abundance (ppm) Unknown
Leading producer Unknown
Reserve base distribution (%) Unknown
Production concentration (%) Unknown
Total governance factor(production) Unknown
Top 3 countries (mined)
  • Unknown
Top 3 countries (production)
  • Unknown
 

Oxidation states and isotopes


Key for Isotopes


Half Life
  y years
  d days
  h hours
  m minutes
  s seconds
Mode of decay
  α alpha particle emission
  β negative beta (electron) emission
  β+ positron emission
  EC orbital electron capture
  sf spontaneous fission
  ββ double beta emission
  ECEC double orbital electron capture

Terminology


Common Oxidation states
The oxidation state of an atom is a measure of the degree of oxidation of an atom. It is defined as being the charge that an atom would have if all bonds were ionic. Free atoms have an oxidation state of 0, and the sum of oxidation numbers within a substance must equal the overall charge.


Important Oxidation states
The most common oxidation states of an element in its compounds.


Isotopes
Elements are defined by the number of protons in its centre (nucleus), whilst the number of neutrons present can vary. The variations in the number of neutrons will create elements of different mass which are known as isotopes.

Oxidation states and isotopes

 
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 
 

Pressure and temperature - advanced terminology


Molar Heat Capacity (J mol-1 K-1)

Molar heat capacity is the energy required to heat a mole of a substance by 1 K.


Young's modulus (GPa)

Young's modulus is a measure of the stiffness of a substance, that is, it provides a measure of how difficult it is to extend a material, with a value given by the ratio of tensile strength to tensile strain.


Shear modulus (GPa)

The shear modulus of a material is a measure of how difficult it is to deform a material, and is given by the ratio of the shear stress to the shear strain.


Bulk modulus (GPa)

The bulk modulus is a measure of how difficult to compress a substance. Given by the ratio of the pressure on a body to the fractional decrease in volume.


Vapour Pressure (Pa)

Vapour pressure is the measure of the propensity of a substance to evaporate. It is defined as the equilibrium pressure exerted by the gas produced above a substance in a closed system.

Pressure and temperature data – advanced

 
Molar heat capacity
(J mol-1 K-1)
Unknown Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) Unknown
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - - - - - - - - -
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History

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.

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Podcasts

Listen to Astatine Podcast
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 elementis brought to you by the Royal Society of Chemistry and produced by thenakedscientists dot com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld dot org forward slash elements.       

 

(End promo)   

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Resources

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References

 
Images:  Visual Elements © Murray Robertson 2011
Mining and Sourcing data:  British Geological Survey – natural environment research council.
Text:  John Emsley Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, 2nd Edition, 2011.
Additional information for platinum, gold, neodymium and dysprosium obtained from Material Value Consultancy Ltd www.matvalue.com
Data: CRC Handbook of Chemistry and Physics, CRC Press, 92nd Edition, 2011.
G. W. C. Kaye and T. H. Laby Tables of Physical and Chemical Constants, Longman, 16th Edition, 1995.
Members of the RSC can access these books through our library.