Actinide

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Atomic No.	Name	Symbol
89	Actinium	Ac
90	Thorium	Th
91	Protactinium	Pa
92	Uranium	U
93	Neptunium	Np
94	Plutonium	Pu
95	Americium	Am
96	Curium	Cm
97	Berkelium	Bk
98	Californium	Cf
99	Einsteinium	Es
100	Fermium	Fm
101	Mendelevium	Md
102	Nobelium	No

The actinide series encompasses the 14 chemical elements that lie between actinium and nobelium (inclusively) on the periodic table, with atomic numbers 89 - 102. The actinide series is named after actinium. All actinides are f-block elements. There are also alternative arrangements which exclude actinium and/or include the transition metal lawrencium. Lawrencium, though a d-block element, is expected to have properties more similar to the actinides than to the transition metals. The actinide series is included in some definitions of the rare earth elements.

The actinides display less similarity in their chemical properties than the lanthanide series, for instance exhibiting a wider range of oxidation states, which initially led to confusion as to whether actinium, thorium, and uranium should be considered d-block elements. All actinides are radioactive.

Only actinium, thorium, and uranium occur naturally in the earth's crust in anything more than trace quantities. Neptunium and Plutonium have been known to show up naturally in trace amounts in uranium ores as a result of decay or bombardment. The remaining actinides were discovered in nuclear fallout, or were synthesized in particle colliders. The latter half of the series possess exceedingly short half-lives.

The actinides are typically placed below the main body of the periodic table, in the manner of a footnote. The full-width version of the periodic table shows the position of the actinides more clearly.

An Organometallic compound of an actinide is known as an organoactinide.

Note that the International Union of Pure and Applied Chemistry (IUPAC) are currently recommending the name actinoid rather than actinide, as the suffix "-ide" is generally used to indicate anions.

[edit] History of the actinide series

During his Manhattan Project research in 1944, Glenn T. Seaborg experienced unexpected difficulty isolating Americium (95) and Curium (96). He began wondering if these elements more properly belonged to a different series which would explain why the expected chemical properties of the new elements were different. In 1945, he went against the advice of colleagues and proposed the most significant change to Mendeleev's periodic table to have been accepted universally by the scientific community: the '''actinide series'''.

In 1945, Seaborg published his actinide concept of heavy element electronic structure, predicting that the actinides would form a transition series analogous to the rare earth series of lanthanide elements.

In 1961, Antoni Przybylski discovered a star that contained unusally high amounts of actinides.

[edit] References

Periodic tables
Standard table \| Vertical table \| Table with names \| Names and atomic masses (large) \| Names and atomic masses (small) \| Names and atomic masses (text only) \| Inline F-block \| Elements to 218 \| Electron configurations \| Metals and nonmetals \| Table by blocks \| Alternatives
Lists of elements
Name \| Atomic symbol \| Atomic number \| Boiling point \| Melting point \| Density \| Atomic mass
Groups: 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18
Periods: 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9
Series: Alkalis - Alkaline earths - Lanthanides - Actinides - Transition metals - Poor metals - Metalloids - Nonmetals - Halogens - Noble gases
Blocks: s-block - p-block - d-block - f-block - g-block