Artificial elements actinides

The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

Most of the larger actinides do not exist in nature. Scientists have created them artificially in the laboratory. Neptunium was first created in 1940, but lawrencium not until 1961. While these artificial elements are interesting, they are not particularly useful because they are so costly to make and because, being very unstable, they do not last very long. 

The transuranium elements up to 106 were synthesized by accelerating neutrons or very light nuclei into other actinides including costly, unstable artificial elements such as californium (98). In 1973, Yuri Oganessian (1933- ) and Alexander G. Demin in Dubna developed the concept of soft fusion or cold fusion (not to be confused with the unrelated cold fusion debacle of 1989) which they successfully... 

Transactinide elements Artificial elements beyond the actinide elements, beginning with ratherfordium (Rf), element 104. The heaviest elements, synthesized until now, are the elements 114, 116, and 118. At present, bohrium (Bh), element 107, is the heaviest element which has been characterized chemically chemical studies of element 108, hassium (Hs), and element 112 are in preparation. 

A further group of elements, the transuranium elements, has been synthesized by artificial nuclear reactions in the period from 1940 onwards their relation to the periodic table is discussed fully in Chapter 31 and need not be repeated here. Perhaps even more striking today are the predictions, as yet unverified, for the properties of the currently non-existent superheavy elements.Elements up to lawrencium (Z = 103) are actinides (5f) and the 6d transition series starts with element 104. So far only elements 104-112 have been synthesized, ) and, because there is as yet no agreement on trivial names for some of these elements (see pp. 1280-1), they are here referred to by their atomic numbers. A systematic naming scheme was approved by lUPAC in 1977 but is not widely used by researchers in the field. It involves the use of three-letter symbols derived directly from the atomic number by using the... 

Prior to 1940 only the naturally occurring actinides (thorium, protactinium and uranium) were known the remainder have been produced artificially since then. The transactinides are still being synthesized and so far the nine elements with atomic numbers 104-112 have been reliably established. Indeed, the 20 manmade transuranium elements together with technetium and promethium now constitute one-fifth of all the known chemical elements. 

The artificial actinides are created when atoms of smaller elements are bombarded with fast-moving particles, usually neutrons. 

Transuranic elements Elements of atomic number >92. All are radioactive and produced artificially all are members of the actinide group. 

Neptunium is the first of the subseries of the actinide series known as the traiisuratiic elements—those heavy, synthetic (man-made) radioactive elements that have an atomic number greater than uranium in the actinide series of the periodic table. An interesting fact is that neptunium was artificially synthesized before small traces of it were discovered in nature. More is produced by scientists every year than exists in nature. 

Berkelium is a metallic element located in group 11 (IB) of the transuranic subseries of the actinide series. Berkelium is located just below the rare-earth metal terbium in the lanthanide series of the periodic table. Therefore, it has many chemical and physical properties similar to terbium ( Tb). Its isotopes are very reactive and are not found in nature. Only small amounts have been artificially produced in particle accelerators and by alpha and beta decay. 

Californium is a synthetic radioactive transuranic element of the actinide series. The pure metal form is not found in nature and has not been artificially produced in particle accelerators. However, a few compounds consisting of cahfornium and nonmetals have been formed by nuclear reactions. The most important isotope of cahfornium is Cf-252, which fissions spontaneously while emitting free neutrons. This makes it of some use as a portable neutron source since there are few elements that produce neutrons all by themselves. Most transuranic elements must be placed in a nuclear reactor, must go through a series of decay processes, or must be mixed with other elements in order to give off neutrons. Cf-252 has a half-life of 2.65 years, and just one microgram (0.000001 grams) of the element produces over 170 mhhon neutrons per minute. 

Californium is a transuranic element of the actinide series that is homologous with dysprosium (gjDy), just above it in the rare-earth lanthanide series. Cf-245 was the first isotope of californium that was artificially produced. It has a half-life of just 44 minutes. Isotopes of californium are made by subjecting berkelium to high-energy neutrons within nuclear reactors, as follows + (neutrons and A, gamma rays) — °Bk — °Cf + (3- (beta particle... 

Among the natural and artificial radioactive elements (Tc, Pm, Po, Fr, Ra, Ac, and actinides), coordination and organometallic compounds of only technetium and the actinide series (An) are well represented at the present time. The interest in their metal complexes has been motivated by the extended use of Tc, available in kilogram amounts, for medical and technical purposes, meanwhile actinides are important on their own for the nuclear industry. A lot of original papers, reviews, and chapters of some books are dedicated to Tc and An complexes [263-281], In the present section, dedicated to the coordination and organometallic chemistry of the actinides and Tc, we intend to present the synthetic techniques for these compounds according to their ligand nature. 

Beyond element 92 (U) lie the transuranic elements of the actinide series. These are all artificial but 2< Pu is of interest because it is produced in nuclear reactors from 2 fU and may be released to the environment from accidents or weapons testing. It has a very long half life (2.4 x 104 years) and is a very dangerous alpha emitter, but, like radon, its geochemistry is too specialised to be included in this chapter. Choppin and Stout (1991) have written an overview of the general chemistry of Pu, to mark the 50th anniversary of its original isolation, and Rai et al. (1980) have discussed its soil chemistry. 

There is nothing like the development of the periodic table through time to give one a sense of the pace of chemical discovery. Lavoisier listed close to thirty elements, and this number more than doubled when Mendeleev invented the periodic table. Since then, we have added the lanthanides and actinides, as well as a stream of artificial radioactive elements. 

The actinides are all radioactive elements. Actinium, thorium, protactinium, and uranium are the only four actinides that have been found in the environment the others are artificial, being produced through various nuclear reactions. It should be noted that at the creation of the universe some amount of Pu could have been formed however, with an 80 million year half-life, it would have fully decayed during the past 10 billion years. 

The analytical chemistry of the transition elements see Transition Metals), that is, those with partly filled shells of d (see (f Configuration) or f electrons see f-Block Metals), should include that of the first transition period (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) and that of the second transition series (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, and Ag). The third transition series embraces Hf, Ta, W, Re, Os, Ir, Pt, and An, and although it formally begins with lanthanum, for historical reasons this element is usually included with the lanthanoids (rare-earth elements) see Scandium, Yttrium the Lanthanides Inorganic Coordination Chemistry Rare Earth Elements). The actinoid elements see Actinides Inorganic Coordination Chemistry) are all radioactive see Radioactive Decay) and those with atomic number see Atomic Number) greater than uranium (Z = 92) are artificial the analytical chemistry of these elements is too specialized to consider here. 

The silicides of the lanthanides and actinides are given in Table 1. Most of the lanthanides (the artificial Pm excluded) form the silicides MjSij, M5Si4, MSi, MSij, whereas the M3Si2 phases have been observed only for Ce and Pr. Phases with the composition MjSi are known only for the elements in the second half of the series except for Tm and Yb. 

All actinide elements of the 5/series are radioactive. Th and U are long lived and occur in minerals that also contain their radioactive decay products. Elements beyond uranium are made artificially, by bombardment with neutrons or with nuclei. Uranium and plutonium are used as nuclear fuels. 

The actinides, or actinoids, have atomic numbers between 89 and 102 and are named for the first element in that series, actinium. The actinides are often called the transuranium elements and include the three heaviest naturally occurring elements in the periodic table—thorium, protactinium, and uranium. Protactinium is rare, but uranium and thorium are found in significant amounts in the Earths crust. The remaining actinides are synthetic, which means they are produced through artificial means. 

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