The actinoid (IUPAC nomenclature) or actinide (traditional nomenclature still in wide use) series encompasses the 15 chemical elements that lie between (and inclusive of) actinium and lawrencium included on the periodic table, with atomic numbers 89 - 103.[1][2][3] The actinoid series derives its name from the first element in the series, actinium, and ultimately from the Greek ακτις (aktis), "ray," reflecting the elements' radioactivity.
The actinoid series (An) is included in some definitions of the rare earth elements. IUPAC is currently recommending the name actinoid rather than actinide. The suffix -ide can indicate one of a group of related compounds (azide, polysaccharide), a binary compound of a nonmetal (bromide, arsenide) or one of a group of several elements (lanthanide, actinide), while -oid means "similar to"). There are alternative arrangements of the periodic table that exclude actinium or lawrencium from appearing together with the other actinoids.
Chemistry
The actinoids display less similarity in their chemical properties than the lanthanoid (lanthanide) series (Ln), 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 actinoids are radioactive.
The actinoids are typically placed below the main body of the periodic table (below the lanthanoid series), in the manner of a footnote. The full-width version of the periodic table shows the position of the actinoids more clearly.
An organometallic compound of an actinoid is known as an organoactinoid.
Occurrence
Only thorium and uranium occur naturally in the Earth's crust in anything more than trace quantities. protactinium and actinium, which are both decay products of uranium, are the only remaining actinoids that were discovered in nature before they were synthesized. Neptunium and plutonium have also been known to show up naturally in trace amounts in uranium ores as a result of decay or bombardment, but this was only discovered after they were synthesized. The remaining actinoids were discovered in nuclear fallout or were synthesized in particle colliders or nuclear reactors, and none of them has been found to occur naturally on earth. Actinoids beyond californium possess exceedingly short half-lives.
Isotopes of all of the actinoids up to and including fermium can be produced by heavy neutron bombardment of lighter nuclides. Such conditions occur naturally in supernovae, and artificially in nuclear explosions and some specialized nuclear reactors.
History
From the earlier known chemical properties of actinium (89) up to uranium (92), indicating a relationship to the transition metals, it was generally assumed that the transuraniums would have similar qualities. During his Manhattan Project research in 1944, Glenn T. Seaborg experienced unexpected difficulty isolating americium (95) and curium (96).[4] He began wondering if these elements more properly belonged to a different series from the transition metals, which would explain why the 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 actinoids would form a transition series analogous to the rare earth series of lanthanoid elements.
In 1961, Antoni Przybylski discovered a star, HD 101065, commonly called Przybylski's star, that contains unusually high amounts of actinoids.
See also
References
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