Astatine

Chaitra 26/06/2026 19:58:09 Updated 26/06/2026 19:58:09

Property	Value
Atomic Number	85
Element	Astatine
Symbol	At
Atomic Mass	[210] (most stable isotope)
Number of Neutrons	125 (Astatine-210)
Number of Protons	85
Number of Electrons	85
Period	6
Group	17
Phase	Solid (predicted)
Radioactive	Yes
Natural	Yes (trace amounts from radioactive decay)
Metal	No
Nonmetal	Yes (often classified as metalloid-like)
Metalloid	Sometimes classified
Type	Halogen
Atomic Radius	127 pm (estimated)
Electronegativity	2.20 (Pauling scale, estimated)
First Ionization Energy	9.30 eV (estimated)
Density	~7 g/cm³ (estimated)
Melting Point	~302 °C (estimated)
Boiling Point	~337 °C (estimated)
Number of Isotopes	No stable isotopes (At-210 most notable)
Discoverer	Dale R. Corson, Kenneth Ross MacKenzie, Emilio Segrè
Year	1940
Specific Heat	— (not well established)
Number of Shells	6
Number of Valence Electrons	7