Living Reference Work Entry

Encyclopedia of Geochemistry

Part of the series Encyclopedia of Earth Sciences Series pp 1-1

Date: Latest Version


  • Monica VasiliuAffiliated withDepartment of Chemistry, The University of Alabama Email author 
  • , David A. DixonAffiliated withDepartment of Chemistry, The University of Alabama Email author 

Element Data

Atomic Symbol: At

Atomic Number: 85

Atomic Weight: (210)

Isotopes (radioactive): 210At, (t1/2 = 8.1 h), 211At, (t1/2 = 7.2 h)

1 Atm Melting Point: 575 K (estimate)

1 Atm Boiling Point: 610 K (estimate)

Common Valences: +5, +1, −1

Ionic Radii: (+V) 57, (−I) 227 ppm

Pauling Electronegativity: 2.2

First Ionization Potential: 899.0 kJ/mol

Chondritic (CI) Abundance:

Silicate Earth Abundance:

Crustal Abundance: trace amount in some minerals

Seawater Abundance: −

Core Abundance:


Astatine (Emsley 1991, 2001) is a reactive, radioactive nonmetal element which resembles iodine. The properties of astatine are not well established. It has been not extensively studied because all its isotopes have short half-lives. Much of what is known about astatine has been estimated from its position in the periodic table, below iodine, and by studying its chemistry in extremely dilute solutions.

History and Use

In 1931 a group of chemists led by Fred Allison reported that they had detected the prev ...

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