actinide series


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actinide series,

a series of radioactive metallic elements in Group 3 of the periodic tableperiodic 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 table entitled
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. Members of the series are often called actinides, although actiniumactinium
[Gr.,=like a ray], radioactive chemical element; symbol Ac; at. no. 89; mass number of most stable isotope 227; m.p. about 1,050°C;; b.p. 3,200°C;±300°C;; sp. gr. 10.07; valence +3. Actinium is a silver-white metal with a cubic crystalline structure.
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 (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) thoriumthorium
[from Thor], radioactive chemical element; symbol Th; at. no. 90; mass number of most stable isotope 232; m.p. about 1,750°C;; b.p. about 4,790°C;; sp. gr. 11.7 at 20°C;; valence +4.

Thorium is a soft, ductile, lustrous, silver-white, radioactive metal.
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, protactiniumprotactinium
, radioactive chemical element; symbol Pa; at. no. 91; mass number of most stable isotope 231; m.p. greater than 1,600°C;; b.p. 4,026°C;; sp. gr. 15.37 (calculated); valence +4, +5. Protactinium is a malleable, shiny silver-gray radioactive metal.
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, uraniumuranium
, radioactive metallic chemical element; symbol U; at. no. 92; mass number of most stable isotope 238; m.p. 1,132°C;; b.p. 3,818°C;; sp. gr. 19.1 at 25°C;; valence +3, +4, +5, or +6.
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, neptuniumneptunium
, radioactive chemical element; symbol Np; at. no. 93; mass number of most stable isotope 237; m.p. about 640°C;; b.p. 3,902°C; (estimated); sp. gr. 20.25 at 20°C;; valence +3, +4, +5, or +6. Neptunium is a ductile, silvery radioactive metal.
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, plutoniumplutonium
, radioactive chemical element; symbol Pu; at. no. 94; mass no. of most stable isotope 244; m.p. 641°C;; b.p. 3,232°C;; sp. gr. 19.84 at 20°C;; valence +3, +4, +5, or +6.
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, americiumamericium
, artificially produced radioactive chemical element; symbol Am; at. no. 95; mass no. of most stable isotope 243; m.p. about 1,175°C;; b.p. about 2,600°C;; sp. gr. 13.67 at 20°C;; valence +2, +3, +4, +5, or +6.
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, curiumcurium
, artificially produced radioactive chemical element; symbol Cm; at. no. 96; mass no. of most stable isotope 247; m.p. about 1,340°C;; b.p. 3,110°C;; sp. gr. 13.5 (calculated); valence +3, +4.
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, berkeliumberkelium
[from Berkeley], artificially produced radioactive chemical element; symbol Bk; at. no. 97; mass no. of most stable isotope 247; m.p. about 1,050°C;; b.p. about 2,590°C;; sp. gr. 14 (estimated); valence +3, +4.
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, californiumcalifornium
[from California], artificially produced, radioactive metallic chemical element; symbol Cf; at. no. 98; mass no. of most stable isotope 251; m.p. about 900°C;; b.p. about 1,470°C;; density unknown; valence +3.
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, einsteiniumeinsteinium
[for Albert Einstein], artificially produced radioactive chemical element; symbol Es; at. no. 99; mass no. of most stable isotope 252; m.p. about 860°C;; b.p. and sp. gr. unknown; valence +2, +3.
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, fermiumfermium
[for Enrico Fermi], artificially produced radioactive chemical element; symbol Fm; at. no. 100; mass no. of most stable isotope 257; m.p. 1,527°C;; b.p. and sp. gr. unknown; valence +2, +3. Fermium is a member of Group 3 of the periodic table.
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, mendeleviummendelevium
, artificially produced radioactive chemical element; symbol Md; at. no. 101; mass no. of most stable isotope 258; m.p. 827°C;; b.p. and sp. gr. unknown; valence +1, +2, +3. Mendelevium is a metal of the actinide series in Group 3 of the periodic table.
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, nobeliumnobelium
, artificially produced radioactive chemical element; symbol No; at. no. 102; mass no. of most stable isotope 259; m.p. 827°C;; b.p. and density unknown; valence +2, +3. It is a metal of the actinide series in Group 3 of the periodic table.
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, and lawrenciumlawrencium,
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.
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. 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 elementssynthetic 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.
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).

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 serieslanthanide 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.
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. 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 elementstransuranium 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.
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. Elements with atomic numbers greater than 103 are not members of the actinide series; element 104 (rutherfordiumrutherfordium
, artificially produced radioactive chemical element; symbol Rf; at. no. 104; mass number of most stable isotope 265; m.p., b.p., and sp. gr. unknown; valence +4.
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) is the first of the transactinide elementstransactinide elements
, in chemistry, elements with atomic numbers greater than that of lawrencium (at. no. 103), the last member of the actinide series. See transuranium elements.
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.

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).

actinide series

[′ak·tə‚nīd ′sir‚ēz]
(chemistry)
The group of elements of atomic number 89 through 103. Also known as actinoid elements.

actinide series

a series of 15 radioactive elements with increasing atomic numbers from actinium to lawrencium