actinide series definition of actinide series in the Free Online Encyclopedia.

actinide series, a series of radioactive metallic elements in Group 3 of the periodic table periodic table, chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley . In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the
..... Click the link for more information. . Members of the series are often called actinides, although actinium actinium (ăktĭn`ēəm) [Gr.,=like a ray], radioactive chemical element; symbol Ac; at. no. 89; at. wt. 227.0278; m.p.
..... Click the link for more information. (at. no. 89) is not always considered a member of the series. The series always includes the 14 elements with atomic numbers 90 through 103. The other members are (in order of increasing atomic number) thorium thorium (thôr`ēəm) [from Thor], radioactive chemical element; symbol Th; at. no. 90; at. wt. 232.0381; m.p.
..... Click the link for more information. , protactinium protactinium (prō'tăktĭn`ēəm), radioactive chemical element; symbol Pa; at. no. 91; at. wt. 231.0359; m.p.
..... Click the link for more information. , uranium uranium (y
..... Click the link for more information. , neptunium neptunium (nĕpt
..... Click the link for more information. , plutonium plutonium (pl
..... Click the link for more information. , americium americium (ămərĭ`shēəm), artificially produced radioactive chemical element; symbol Am; at. no. 95; mass no.
..... Click the link for more information. , curium curium (ky
..... Click the link for more information. , berkelium berkelium (bûr`klēəm) [from Berkeley ], artificially produced radioactive chemical element; symbol Bk; at. no. 97; mass no.
..... Click the link for more information. , californium californium (kăl`ĭfôr'nēəm)
..... Click the link for more information. , einsteinium einsteinium (īn`stī'nēəm, īnstī`–)
..... Click the link for more information. , fermium fermium (fûr`mēəm) [for Enrico Fermi ], artificially produced radioactive chemical element; symbol Fm; at. no. 100; mass no.
..... Click the link for more information. , mendelevium mendelevium (mĕndəlāv`ēəm), artificially produced radioactive chemical element; symbol Md; at. no. 101; mass no.
..... Click the link for more information. , nobelium nobelium (nōbē`lēəm), artificially produced radioactive chemical element; symbol No; at. no. 102; mass no.
..... Click the link for more information. , and lawrencium lawrencium, artificially produced radioactive chemical element; symbol Lr; at. no. 103; mass number of most stable isotope 262; m.p. about 1,627°C;; b.p. and sp. gr. unknown; valence +3.
..... Click the link for more information. . Thorium and uranium are the only actinides found in the earth's crust in appreciable quantities, although small amounts of neptunium and plutonium have been found in uranium ores. Actinium and protactinium are found in nature as decay products of some thorium and uranium isotopes. All the others have only been synthesized in small quantities (see synthetic elements synthetic elements, in chemistry, radioactive elements that were not discovered occurring in nature but as artificially produced isotopes. They are technetium (at. no. 43), which was the first element to be synthesized, promethium (at. no. 61), astatine (at. no.
..... Click the link for more information. ).

Study of the properties of the actinides is hampered by their radioactive instability. It is known, however, that all members of the series resemble actinium and each other in their chemical properties and that they have a strong chemical resemblance to their homologs in the lanthanide series lanthanide series, a series of metallic elements, included in the rare-earth metals , in Group 3 of the periodic table . Members of the series are often called lanthanides, although lanthanum (atomic number 57) is not always considered a member of the series.
..... Click the link for more information. . The actinides are reactive and assume a number of different valences in their compounds. As the atomic number increases in this series, added electrons enter the 5f electron orbital. Elements in this series with atomic numbers greater than that of uranium (92) are called transuranium elements transuranium elements, in chemistry, radioactive elements with atomic numbers greater than that of uranium (at. no. 92). All the transuranium elements of the actinide series were discovered as synthetic radioactive isotopes at the Univ.
..... Click the link for more information. . Elements with atomic numbers greater than 103 are not members of the actinide series; element 104 (rutherfordium rutherfordium (rŭth'ərfôr`dēəm), artificially produced radioactive chemical element; symbol Rf; at. no.
..... Click the link for more information. ) is the first of the transactinide elements transactinide elements (trăns'ăk`tənīd'), in chemistry, elements with atomic numbers greater than that of lawrencium (at.
..... Click the link for more information. .

Bibliography

See A. J. Freeman and G. H. Lander, ed., Handbook on the Physics and Chemistry of the Actinides (1984); S. Cotton, Lanthanides and Actinides (1991).