Inorganic Chemicals

Symbol: Ac; a radioactive element; atomic number 89; atomic weight 227.028; electronic config. [Rn]6d17s2; oxidation state +3; the principal isotope is 227Ac, t½ 21.77 y; emits beta rays forming thorium-227, radium-223 and several short-lived isotopes of radon, polonium, bismuth and lead; a minor isotope is 228Ac, t½ 6.15 hr, a beta-emitter producing thorium-228; also several other minor isotopes are known which include: 225Ac (t½ 10 ± 0.1 d), 226Ac (t½ 1.224 d), 224Ac (t½ 2.7 hr), 229Ac (t½ 1.04 hr), 231Ac (t½ 7.5 min), 233Ac (t½ 2.4 min), 223Ac (t½ 2.1 min), 230Ac (t½ 2.03 min), and 232Ac (t½ 2.0 min).

Occurrence, Preparation and Uses
Actinium-227 occurs in uranium ore and is a decay product of uranium-235. It is found in equilibrium with its decay products. It is prepared by bombarding radium atoms with neutrons. Chemically, the metal is produced by reducing actinium fluoride with lithium vapor at 1,100°C to 1,300°C.

The element was discovered independently by A. Debierne and F. Giesel in 1899 and 1902, respectively. It is used in nuclear reactors as a source of neutrons.

Physical Properties
Silvery metal; cubic crystal; melts at 1,051°C; vaporizes at 3,198°C; density 10.0 g/cm3

Chemical Reactions
Actinium behaves like lanthanum forming mostly the trivalent salts of the metal. It is strongly electropositive, the first ionization potential being 5.17eV. Reacts with HCl forming AcCl3; also reacts with organic acids forming corresponding salts; combustion in air can produce oxide and nitride; susceptible to react with CO2 forming carbonate.

Analysis
The radioactivity can be measured by a beta counter. The metal at trace
concentrations can be determined by an atomic absorption or emission spectrophotometer.

Toxicity
Exposure to radiation can cause cancer.