Astatine

85

At

(210)

  • Name: Astatine
  • Symbol: At
  • Atomic number: 85
  • Atomic weight: (210)
  • CAS Registry ID: 7440-68-8
  • Group name: Halogen
  • Period number: 6
  • Block: p-block
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Description

Astatine is a radioactive halogen that occurs from the decay of uranium-235 and uranium-238. It is the heaviest of all the halogens and has been named the rarest element on Earth. Astatine has an atomic weight of 210, a melting point of 576 °F, and the boiling point of this element is not currently known. Compounds of astatine have been created and studied for possible applications in nuclear medicine, but currently there are no commercial uses for astatine as it is so rare and toxic.

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Isolation

The quick half life of astatine makes isolation procedures from nature impossible. As this element is not obtainable from natural sources it must be created instead.

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Astatine only has a half life of approximately 8.3 hours. Any studies or projected work that is to be done on astatine that is synthesized must be performed quickly before it disintegrates. The only way that astatine can be created is in a nuclear reactor using the element bismuth. In this process, the bismuth isotope, number 209, is bombarded with alpha particles from the nuclei of the isotope, number 4, of helium. This results in the formation of the astatine isotope number 211. The bismuth target must be cooled during this process because astatine is extremely volatile. Once this process is completed, the bismuth target is then heated to between 300 - 1112 °F. The heating process takes place under nitrogen and this reaction produces a stream of astatine in its elemental form. The minute quantities of astatine that are produced are then collected on a finger of cold glass.


General
Name Astatine
Symbol At
Number 85
Chemical series halogens
Group 17
Period 6
Block p
Appearance metallic
Standard atomic weight (210)  g·mol−1
Electron configuration [Xe] 4f14 5d10 6s2 6p5
Electrons per shell 2, 8, 18, 32, 18, 7
Atomic properties
Crystal structure
Oxidation states ±1, 3, 5, 7
Electronegativity 2.2 (scale Pauling)
Ionization energies 1st: 890±40 kJ/mol
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Atomic radius
Atomic radius (calc.)
Covalent radius
Van der Waals radius
Physical properties
Phase solid
Density (near r.t.)
Liquid density at m.p.
Melting point 575 K (302 °C, 576 °F)
Boiling point 610 K (337 °C, ? 639 °F)
Critical point
Heat of fusion
Heat of vaporization ca. 40  kJ·mol−1
Heat capacity
Miscellaneous
Magnetic ordering
Electrical resistivity
Thermal conductivity (300 K) 1.7  W·m−1·K−1
Thermal expansion
Speed of sound (thin rod)
Young's modulus
Shear modulus
Bulk modulus
Poisson ratio
Mohs hardness
Vickers hardness
Brinell hardness
CAS registry number 7440-68-8

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