A highly unstable radioactive element (the heaviest of the halogen series); a decay product of uranium and thorium; SYN. At, atomic number 85.
Radioactive element of the halogen group.
Nonmetallic, radioactive element, symbol At, atomic number 85, atomic weight 210. It is a member of the halogen group, and is very rare in nature. Astatine is highly unstable, with at least 19 isotopes; the longest lived has a half-life of about eight hours.

Astatine.

ETYM Pref. a- not + static.
Not static or stable.
In equilibrium, unstable; in neutral equilibrium; Electricity, not tending to assume a definite position.

A highly unstable radioactive element (the heaviest of the halogen series); a decay product of uranium and thorium; SYN. At, atomic number 85.
Radioactive element of the halogen group.
Nonmetallic, radioactive element, symbol At, atomic number 85, atomic weight 210. It is a member of the halogen group, and is very rare in nature. Astatine is highly unstable, with at least 19 isotopes; the longest lived has a half-life of about eight hours.

Astatine.