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Astatine

From Academic Kids

polonium - astatine - radon
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At
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At-TableImage.png
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General
Name, Symbol, Number Astatine, At, 85
Series Halogens
Group, Period, Block 17 (VIIA), 6, p
Density, Hardness no data, no data
Appearance metallic
Atomic properties
Atomic weight [210] amu
Atomic radius no data
Covalent radius 127 pm
van der Waals radius no data
Electron configuration [Xe]4f14 5d10 6s2 6p5
e- 's per energy level 2, 8, 18, 32, 18, 7
Oxidation states (Oxide)  ?1,3,5,7 (unknown)
Crystal structure no data
Physical properties
State of matter solid
Melting point 575 K (576 ?F)
Boiling point 610 K (639 ?F)
Molar volume no data
Heat of vaporization no data
Heat of fusion 114 kJ/mol
Vapor pressure no data
Speed of sound no data
Miscellaneous
Electronegativity 2.2 (Pauling scale)
Specific heat capacity no data
Electrical conductivity no data
Thermal conductivity 1.7 W/(m*K)
1st ionization potential 920 kJ/mol (estimated)
Most stable isotopes
iso NA half-life DM DE MeV DP
210At 100% 8.1 h Epsilon
Alpha
3.981
5.631
210Po
206Bi
SI units & STP are used except where noted.

Astatine is a chemical element in the periodic table that has the symbol At and atomic number 85. This radioactive element occurs naturally from uranium and thorium decay and is the heaviest of the halogens.

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Contents

Notable characteristics

This highly radioactive element has been confirmed by mass spectrometers to behave chemically much like other halogens, especially iodine (it probably accumulates in the thyroid gland like iodine). Astatine is thought to be more metallic than iodine. Researchers at the Brookhaven National Laboratory have performed experiments that have identified and measured elementary reactions that involve astatine.

With the possible exception of francium, 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 one time; this amounts to less than one teaspoon of the element.

History

Astatine (Greek astatos meaning "unstable") was first synthesized in 1940 by Dale R. Corson, K. R. MacKenzie, and [[Emilio Segr蝝 of the University of California, Berkeley by barraging bismuth with alpha particles. An earlier name for the element was alabamine (Ab).

Occurrence

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

Isotopes

Astatine has 41 known isotopes, all of which are radioactive; the longest-lived isotope is 210At which has a half-life of 8.1 hours. The shortest-lived isotope is 213At which has a half-life of 125 nanoseconds.

References

External links

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