Astatine

At a glance

Symbol

At

Atomic number

85

Mass number of its longest-lived isotope

[210]

Group

17

Period

6

Family

halogen

Electron configuration

[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵

Valence electrons

7

Electronegativity

2.20

Common ions

At⁻, and positive states such as At⁺

Isotopes

none are stable; ²¹⁰At lasts longest, with a half-life of about 8 hours

On the table

Period 6, group 17. The other halogens are tinted, and every cell opens its own article.

Electrons and bonding

Seven valence electrons, like the other halogens, but it is the most metal-like of them. Only trace amounts have ever been studied.

Properties

State at 25 °C

solid

What it looks like

never seen; a visible sample would vaporize itself with the heat of its own radioactivity

Melting point

302 °C (estimated)

Boiling point

not known

Density

not measured

Where it is found

Formed briefly in uranium and thorium ores as they decay. Estimates of how much exists in all of Earth's crust at any moment range from under a gram to about an ounce.

Discovery and name

Dale Corson, Kenneth MacKenzie and Emilio Segrè made it in 1940 at Berkeley by bombarding bismuth with alpha particles. It was named from the Greek astatos, unstable.