Actinium (Ac)

Isotopes of Actinium

Isotope Atomic Mass Half-life Mode of Decay Nuclear Spin Nuclear Magnetic Moment
Ac-224  224.021708  2.7 hours  β- to Th-224;
α to Fr-220;
EC to Ra-224		 0 No data available 
Ac-225  225.02322  10.0 days  α to Fr-221 3/2  No data available 
Ac-226 226.026089 1.224 days β- to Th-226;
α to Fr-222;
EC to Ra-226		 1 No data available 
Ac-227 227.027750 21.77 years β- to Th-228;
α to Fr-224		 3/2 1.1
Ac-228 228.031104 6.15 hours β- to Th-229 3 No data available 
Ac-229 229.03293 1.04 hours No data available  3/2 No data available 

Ac

Actinium was discovered in 1899 by André-Louis Debierne. Its name derives from the Greek word aktinos, meaning "ray."

Actinium is a silvery metal with a cubic crystal form. It behaves like lanthanum, forming mostly the trivalent salts of the metal. It is strongly electropositive, the first ionization potential being 5.17 eV. It reacts with HCl, forming AcCl3, and also reacts with organic acids, forming their corresponding salts. Combustion in air can produce oxide and nitride. It is also susceptible to react with CO2, forming carbonate. It is used in nuclear reactors as a source of neutrons. Exposure to its radiation can cause cancer.

Properties of Actinium

Name Actinium 
Symbol Ac 
Atomic number 89 
Atomic weight 227 
Standard state Solid at 298 ºK 
CAS Registry ID 7440-34-8 
Group in periodic table N/A 
Group name Actinoids 
Period in periodic table 7 (Actinoid) 
Block in periodic table f-block 
Color Silvery 
Classification Metallic 
Melting point 1050 ºC
Boiling point 3300 °C
Vaporization point 3198 ºC
Thermal conductivity 12 (estimate) W/(m·K)
Electronegativity 1.1
Heat of vaporization 400 kJ·mol-1
Heat of fusion 14 kJ·mol-1
Density of solid 10.07 g/cm3 
Electron configuration [Rn]6d17s2 
Oxidation state +3 

 

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