Astatine

Astatine,  ₈₅At

General properties
Name, symbol	Astatine, At
Appearance	Unknown, possibly metallic
Astatine in the periodic table
I ↑ At ↓ Ts Polonium ← Astatine → Radium
Atomic number	85
Standard atomic weight (Ar)	210
Group, block	group 17 (halogens); p-block
Period	period 6
Electron configuration	[Xe] 4f14 5d10 6s2 6p5
per shell	2, 8, 18, 32, 18, 7
Physical properties
Unknown, possibly silvery or black
Phase	Unknown, possibly solid
Atomic properties
Electronegativity	Pauling scale: −1, +1, +3, +5, +7
energies	1st: 899.003 kJ/mol
Miscellanea
CAS Registry Number	7440-68-8
History
Naming	After Greek astatos (αστατος), meaning "unstable"
Discovery	Dale R. Corson, Kenneth Ross MacKenzie, Emilio Segrè (1940)

Astatine is a chemical element with the symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements.

All of astatine's isotopes are short-lived: the most stable is astatine-210, with a half-life of 8.1 hours. A sample of the pure element has never been assembled, because any macroscopic specimen, no matter the size, would be immediately vaporized by the heat of its own intense radioactivity.

Properties

Chemical

Chemically, several anionic species of astatine are known and most of its compounds resemble those of iodine, but it also sometimes displays metallic characteristics and shows some similarities to silver.

The chemistry of astatine is "clouded by the extremely low concentrations at which astatine experiments have been conducted, and the possibility of reactions with impurities, walls and filters, or radioactivity by-products, and other unwanted nano-scale interactions".

Astatine has some metallic characteristics as well, such as plating onto a cathode, and coprecipitating with metal sulfides in hydrochloric acid. Some sources indicate that At can form complexes with EDTA.

Physical

The bulk properties of astatine are not known with certainty. Many of them have been estimated based on the element's position on the periodic table as a heavier analog of iodine, and a member of the halogens. However, astatine also falls roughly along the dividing line between metals and nonmetals, and some metallic behavior has also been observed and predicted for it. Astatine is likely to have a dark or lustrous appearance and may be a semiconductor or possibly a metal.

Availability

Astatine occurs in minute traces in natural uranium ores. Astatine is the rarest naturally occurring element, with the total amount of astatine in the Earth's crust is estimated by some to be between 1-30 g.

Isolation

Astatine is far too radioactive to be accumulated in sufficient quantity.

Projects

• Study radioactivity

Handling

Safety

Astatine is highly radioactive, but due to its short half-life, it cannot be accumulated in sufficiently dangerous amounts.

Storage

Astatine cannot and should not be stored. Traces may occur in natural uranium ores.

Disposal

No disposal is required since there's nothing to dispose of.

References

Relevant Sciencemadness threads

• Astatine
• Astatine
• Astatine probable vapor colour