Actinium

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

Property	Value
Atomic Number	89
Element	Actinium
Symbol	Ac
Atomic Mass	[227] (most stable isotope)
Number of Neutrons	138 (Actinium-227)
Number of Protons	89
Number of Electrons	89
Period	7
Group	3
Phase	Solid
Radioactive	Yes
Natural	Yes (from decay of uranium and thorium)
Metal	Yes
Nonmetal	No
Metalloid	No
Type	Actinide
Atomic Radius	~260 pm (estimated)
Electronegativity	1.10 (estimated)
First Ionization Energy	5.17 eV (estimated)
Density	10.07 g/cm³
Melting Point	1050 °C
Boiling Point	3200 °C (estimated)
Number of Isotopes	No stable isotopes (Ac-227 most notable)
Discoverer	Friedrich Oskar Giesel
Year	1899
Specific Heat	0.120 J/g·K (estimated)
Number of Shells	7
Number of Valence Electrons	3