89
227.00
Ac
Actinium
Identification
CAS Number: 7440-34-8
Discovery Year: 1899
Discoverer: André Debierne
Discovery Location: France
Properties
Atomic Dimensions
Atomic Radius: 195 pm →
Atomic Radius (Rahm): 293 pm
Covalent Radius: 215 pm →Van der Waals Radius: 247.00000000000003 pm
Atomic Volume: 22.54 cm³/mol
Lattice Constant: 5.31 Å
Thermodynamics
Melting Point: 1320 K →Boiling Point: 3470 K →Heat of Fusion: 10.5 kJ/mol →Heat of Vaporization: 292.9 kJ/mol →
Heat of Formation: 406 kJ/mol
Electronic Structure
Electron Config: [Rn] 6d 7s2
Block: d
Period: 7 →Group: 3 →Electronegativity: 1.1 →Electron Affinity: 0.35 eV →Oxidation States: +3
Abundance & Geochemistry
Crust Abundance: 5.5e-10 mg/kg
Geochemical Class: U/Th decay series
Goldschmidt Class: synthetic
About
Silvery radioactive metallic element, belongs to group 3 of the periodic table. The most stable isotope, Ac-227, has a half-life of 217 years. Ac-228 (half-life of 6.13 hours) also occurs in nature. There are 22 other artificial isotopes, all radioactive and having very short half-lives. Chemistry similar to lanthanumpy. Used as a source of alpha particles. Discovered by A. Debierne in 1899.
Isotopes
Ac-225 225 ☢ 9.92 d
Ac-227 227 ☢ 21.8 a