85
  At  
210.000000
Astatine

Name: Astatine
Symbol: At
Atomic Number: 85
Atomic Weight: 210.000000
Family:  Halogens
CAS RN: 7440-68-8
Description: A metallic solid member of the halogen family.
State (25C): Solid
Oxidation states: 1, +3, + 5, + 7

Molar Volume:  unknown
Valence Electrons: 6p5

Boiling Point:  610K, 337C, 639F
Melting Point:
575K, 302C,  576F
Electrons Energy Level: 2, 8, 18, 32, 18, 7
Isotopes: 33
Heat of Vaporization: unknown
Heat of Fusion: 114 kJ/mol
Density: unknown
Specific Heat: unknown
Atomic Radius: 1.43
Ionic Radius: unknown
Electronegativity: 2.2 (Pauling); 1.96 (Allrod Rochow)
Astatine is the last of the known halogens. The existence of "eka-iodine" had been predicted by Dimetri Mendeleev.   Astatine (after Greek, astat, astatos, meaning "unsteady") was first synthesized in 1940 by Dale R. Corson, K.R. MacKenzie, and Emilio Segre at the University of California, Berkeley by bombarding targets made of bismuth-209 with high energy alpha particles (helium nuclei).  Astatine 211 is the product and has a half-life of 7.2 hours.  The most stable isotope of Astatine is 210 which has a half-life of 8.1 hours.   An earlier name for the element was alabamine (Ab).

Not much is known about the chemical properties of Astatine but it is expected to react like the other halogens, although much less vigorously, and it should be more metallic than Iodine. There should be tiny quantities of Astatine in the earth's crust as products of other radioactive decays, but their existence would be short-lived.

This highly radioactive element has been confirmed by mass spectrometers to behave chemically much like other halogens, especially Iodine (it would probably accumulate in the thyroid gland like iodine).

9
F
18.99

17
Cl
35.45

35
Br
79.90

53
I
126.9

85
At
210.0

1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10 6s2p5

History

Researchers at the Brookhaven National Laboratory have performed experiments that have identified and measured elementary reactions that involve Astatine; however, chemical research into Astatine is limited by its extreme rarity, which is a result of its extremely short half-life.

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d10
6s2 6p5

Astatine is the rarest naturally-occurring element, with the total amount in Earth's crust estimated to be less than 1 oz (28 g) at any given time; this amounts to less than one teaspoon of the element.  The Guinness Book of records has dubbed the element the rarest on Earth, stating: "Only around 0.9 oz (25 g) of the element Astatine (At) occurring naturally"; Issac Asimov wrote a 1955 essay on large numbers, scientific notation, and the size of the atom, in which he stated that the number of Astatine atoms on Earth at any time was "only a trillion".

Occurrence

Astatine is produced by bombarding Bismuth with energetic alpha particles to obtain relatively long-lived  209At - 211At, which can then be distilled from the target by heating in the presence of air.

Compounds

Multiple compounds of Astatine have been synthesized in microscopic amounts and studied as intensively as possible before their inevitable radioactive disintegration. These compounds are primarily of theoretical interest; however, they are also being studied for potential use in nuclear medicine.

Isotopes

Astatine has 33 known isotopes, all of which are radioactive; the range of their mass numbers is from 191 to 223.  There exist also 23 meta states.  The longest-lived isotope is 210At, which has a half-life of 8.1 hours; the shortest-lived known isotope is 213At, which has a half-life of 125 nanoseconds.

atom.gif (700 bytes)

Isotope Atomic Mass Half-Life
At191    
At192    
At193   ~40 ms
At194 193.999 ~40 ms
At195 194.997 0.63 seconds
At196 195.996 0.253 seconds
At197 196.993 0.35 seconds
At198 197.993 4.2 seconds
At199 198.991 7.2 seconds
At200 199.99 43 seconds
At201 200.988 89 seconds
At202 201.988 184 seconds
At203 202.987 7.4 minutes
At204 203.9873 9.2 minutes
At205 204.986 26.2 minutes
At206 205.9866 30 minutes
At207 206.9858 1.8 hours
At208 207.9866 1.63 hours
At209 208.9862 5.41 hours
At210 209.9871 8.1 hours
At211 210.9875 7.214 hours
At212 211.9907 0.314 seconds
At213 212.9929 125 ns
At214 213.9964 558 ns
At215 214.9986 0.1 ms
At216 216.0024 0.3 ms
At217 217.0047 32.3 ms
At218 218.0087 1.5 seconds
At219 219.0113 56 seconds
At220 220.015 3.71 minutes
At221 221.018 2.3 minutes
At222 222.022 54 seconds
At223 223.025 50 seconds

atom.gif (700 bytes)

Astatine Data

 

Atomic Structure

Atomic Radius (): 1.43
Atomic Volume cm3/mol : unknown
Covalent Radius: 1.45
Crystal Structure: unknown
Ionic Radius: unknown

Chemical Properties

Electrochemical Equivalents: 7.8346g/amp-hr
Electron Work Function: unknown
Electronegativity: 2.2 (Pauling); 1.96 (Allrod Rochow)
Heat of Fusion: 114 kJ/mol
Incompatibilities: unknown
First Ionization Potential: 9.65
Second Ionization Potential: unknown
Third Ionization Potential: unknown
Valence Electron Potential: unknown
Ionization Energy (eV): 9.5 eV

Physical Properties

Atomic Mass Average: 209.9871
Boiling Point: 610K, 337C, 639F
Melting Point: 575K, 302C,  576F
Heat of Vaporization: unknown
Coefficient of Lineal Thermal Expansion/K-1: N/A
Electrical Conductivity: unknown
Thermal Conductivity: 0.017 W/cmK
Density: unknown
Enthalpy of Atomization: 92 kJ/mole @ 25C
Enthalpy of Fusion: unknown
Enthalpy of Vaporization: unknown
Flammability Class: unknown
Molar Volume: unknown
Optical Refractive Index: unknown
Relative Gas Density (Air=1): unknown
Specific Heat: unknown
Vapor Pressure: unknown
Estimated Crustal Abundance: unknown
Estimated Oceanic Abundance: unknown


(Gr. astatos, unstable) Synthesized in 1940 by D.R. Corson, K.R. MacKenzie, and E. Segre at the University of California by bombarding bismuth with alpha particles.   The longest-lived isotopes, with naturally occurring Uranium and Thorium isotopes, and traces of At-217 are equilibrium with U-233 and Np-239 resulting from interaction of thorium and uranium with naturally produced neutrons.  The total amount of Astatine present in the earth's crust, however, is less than 1 oz.   Astatine can be produced by bombarding Bismuth with energetic alpha particles to obtain the relatively long-lived At-209-211, which can be distilled from the target by heating in air.  The "time of flight" mass spectrometer has been used to confirm that this highly radioactive halogen behaves chemically very much like other halogens, particularly Iodine.   Astatine is said to be more metallic than Iodine, and, like Iodine, it probably accumulates in the thyroid gland.  Workers at the Brookhaven National Laboratory have recently used reactive scattering in crossed molecular beams to identify and measure elementary reactions involving Astatine.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond