Symbol: At
Atomic number: 85
Category: halogens
Group: 17
Period: 6
Block: p
Atomic weight: (210) g/mol
Electrons per shell: 2, 8, 18, 32, 18, 7
CAS number: 7440-68-8
Phase: solid
Density: 4.933 kg/dm3 (near room temperature)
Melting point: 575 K (302 C, 576 F)
Boiling point: 610 K (337 C, 639 F)
Crystal structure: unknown
Oxidation states: 1, 3, 5, 7
Electronegativity: 2.2 (Pauling scale)
Name's origin: astatos
Name's meaning: a Greek word which means 'unstable' due to its relatively short half-life of about 8 hours
- is a radioactive element with 33 known isotopes with mass numbers between 191 and 223
- the longest-lived isotope is astatine-210, which has half-life of 8.1 hours; the shortest-lived known isotope is astatine-213, which has a half-life of 125 nanoseconds
- is produced by radioactive decay in nature, due to its short half life it is found only in minute amounts
- the alpha-emitting properties of some astatine isotopes are used for science applications, and also medical applications for astatin
- would be expected to be a nearly black solid, which, when heated, sublimes into a dark, purplish vapor (darker than iodine)
- is the least reactive of the halogens, being less reactive than iodine
- has been proposed with names dakin and helvetium