Periodic Table


Atomic number: 85
Atomic weight: 210
Symbol: At
Group number: 17
Electronic configuration: [Xe].4f14.5d10.6s2.6p5


The longest-lived isotope, 210At, has a half-life of only 8.3 hours. There are about 20 isotopes known, all of which are radioactive. Astatine is a halogen and possibly accumulates in the thyroid like iodine.

General information

Discoveror: Dale Corson, K.R. MacKenzie, and Emilio Segre
Date discovered: 1940
Discovered at: University of California, USA.
Meaning of name: From the Greek word "astatos" meaning "unstable"

Physical data

Standard state: solid at 298 K
Colour: metallic
Density of solid at ambient temperature/kg m-3: no data
Molar volume/cm3: no data

Radii /pm

Atomic: 127
Covalent (single bond):
Pauling radius for the ion [At]-: no data

Valence shell orbital radius maxima (Rmax)
orbital s p d f


Both values are quoted on the Pauling scale.

Pauling: 2.2
Allred Rochow: 1.90

Crystal Structure


The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.


Temperatures (/K)

melting point: 575
boiling point: 273

Enthalpies /kJ mol-1

fusion: 12
vaporization: 30

single bond enthalpies:
At-F At-Cl At-Br At-I At-At
no data no data no data no data 80

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance

Further Information

Copyright 1997 Mark Winter
Department of Chemistry at the University of Sheffield, Sheffield S3 7HF, England.

The current version of this document is at http://www.shef.ac.uk/~chem/web-elements-I/At.html