308 | The History and Use of Our Earth’s Chemical Elements Characteristics

308 | The History and Use of Our Earth’s Chemical Elements Characteristics

Actinium is the last (bottom) member of group 3 (IIIB) of elements in the periodic table and the first of the actinide series of metallic elements that share similar chemical and physical characteristics. Actinium is also closely related in its characteristics to the element lanthanum, which is located just above it in group 3. The elements in this series range from atomic num- ber 89 (actinium) through 103 (lawrencium). Actinium’s most stable isotope is actinium-227, with a half-life of about 22 years. It decays into Fr-223 by alpha decay and Th-227 through beta decay, and both of these isotopes are decay products from uranium-235.

Abundance฀and฀Source Actinium is a rare element that is found in very small amounts in uranium ore (pitch-

blende), making it difficult and expensive to extract even a small quantity. It is less expensive and easier to produce small amounts by bombarding the element radium with neutrons in a nuclear reactor. Actinium has few commercial uses.

History Actinium is another example of an element being discovered independently by two differ-

ent men. After the Curies had separated radium ( 88 Ra) from uranium ( 92 U) ore in 1899, their friend Andre-Louis Debierne (1874–1949) discovered another radioactive element (actinium) mixed with uranium in the ore pitchblende. A few years later, in 1902, Friedrich Otto Giesel also discovered element 89, an element that resembled the rare-earths but was much too heavy to be a rare-earth metal. Although Giesel named element 89 “emanium,” his records were predated by Debierne’s, which gave Debierne credit for the discovery as well as naming rights. He chose the name “actinium,” meaning “ray.”

Common฀Uses There are no significant uses for actinium because of its scarcity and the expense of produc-

ing it. The only practical use for small amounts of actinium is as a tracer in medicine and industry. It is too difficult to produce in substantial quantities to make it useful. Actinium can be used as a source of neutrons to bombard other elements to produce isotopes of those elements, but other neutron sources are less expensive.

Examples฀of฀Compounds Most of the radioactive actinium isotopes that are produced in nuclear reactors are in mil-

ligram quantities. There are not many common compounds. The metallic ion of actinium has an oxidation state of +3. Two examples of Ac 3+ com- pounds follow:

Actinium (III) trifluoride: Ac 3+ + 3F 1- → AcF 3 . Actinium sequioxide: 2Ac 3+ + 3O 2- → Ac 2 O 3 .

Hazards Most of the radioactive isotopes of actinium pose an extreme radiation hazard. They are

bone-seeking radioactive poisons.

309 THORIUM

Guide to the Elements |

SYMBOL:฀Th฀ PERIOD:฀7฀ SERIES฀NAME:฀Actinide฀ ATOMIC฀NO:฀90 ATOMIC฀MASS:฀232.0381฀amu฀ VALENCE:฀4฀ OXIDATION฀STATE:฀+4฀ NATURAL฀STATE:฀

Solid ORIGIN฀OF฀NAME:฀Thorium฀was฀named฀for฀Thor,฀the฀Scandinavian฀(Norse)฀god฀of฀“thun- der.” ISOTOPES:฀There฀are฀30฀radioisotopes฀of฀thorium.฀One฀isotope฀in฀particular,฀thorium-232,฀ although฀a฀weak฀source฀of฀radiation,฀has฀such฀a฀long฀half-life฀(1.405×10 ฀+10 ฀years,฀or฀

about฀14฀billion฀years)฀that฀it฀still฀exists฀in฀nature฀and฀is฀considered฀stable. ELECTRON฀CONFIGURATION

฀ Energy฀Levels/Shells/Electrons฀ Orbitals/Electrons ฀

s2,฀p6

฀ 3-M฀=฀18฀

s2,฀p6,฀d10

฀ 4-N฀=฀32฀

s2,฀p6,฀d10,฀f14

฀ 5-O฀=฀18฀

s2,฀p6,฀d10