Elements, 2, 5-7 actinide series metallics

Actinide elements (Z = 89 - 103) include the heaviest natural and most of the synthetic transuranium elements. They form a series of transition elements, characterized by the filling of an inner - the 5f-electron shell. The elements from Ac (Z = 89) to Es (Z = 99) are available in quantities sufficient for solid state studies. Elemental actinides are metallic. The methods of metal preparation and characterization have been improved to yield samples of known purity and crystal structure, sometimes in the form of single crystals. Recent measurements of structural, thermodynamic and electronic properties have emphasized elements in the beginning and in the centre of the actinide series. 

The only crystalline phase which has been isolated has the formula Pu2(OH)2(SO )3(HaO). The appearance of this phase is quite remarkable because under similar conditions the other actinides which have been examined form phases of different composition (M(OH)2SOit, M=Th,U,Np). Thus, plutonium apparently lies at that point in the actinide series where the actinide contraction influences the chemistry such that elements in identical oxidation states will behave differently. The chemistry of plutonium in this system resembles that of zirconium and hafnium more than that of the lighter tetravalent actinides. Structural studies do reveal a common feature among the various hydroxysulfate compounds, however, i.e., the existence of double hydroxide bridges between metal atoms. This structural feature persists from zirconium through plutonium for compounds of stoichiometry M(OH)2SOit to M2 (OH) 2 (S0O 3 (H20) i,. Spectroscopic studies show similarities between Pu2 (OH) 2 (SOO 3 (H20) i, and the Pu(IV) polymer and suggest that common structural features may be present. 

Among the tetraborides, UB4 has the smallest volume and hence the smallest effective radius. Thus an actinide element having a metallic radius of 1.59 A (Pu) or smaller forms a diboride, while those having larger radii do not. As in the rare-earth series, the actinides able to form MB4, MBg and MB,2 borides form also MB2 diborides (Table 1). 

Krebs, Robert E. The history and use of our earth s chemical elements a reference guide. Westport (CT) Greenwood P, 1998. ix, 346p. ISBN 0-313-30123-9 A short history of chemistry — Atomic structure The periodic table of the chemical elements — Alkali metals and alkali earth metals - Transition elements metals to nonmetals — Metallics and metalloids - Metalloids and nonmetals — Halogens and noble gases - Lanthanide series (rare-earth elements) — Actinide, transuranic, and transactinide series... 

Transition metah—found in the groups located in the center of the periodic table, plus the lanthanide and actinide series. They are all solids, except mercury, and are the only elements whose shells other than their outer shells give up or share electrons in chemical reactions. Transition metals include the 38 elements from groups 3 through 12. They exhibit several oxidation states (oxidation numbers) and various levels of electronegativity, depending on their size and valence. 

Actinium is the last (bottom) member of group 3 (IIIB) of elements in the periodic table and the first of the actinide series of metallic elements that share similar chemical and physical characteristics. Actinium is also closely related in its characteristics to the element lanthanum, which is located just above it in group 3. The elements in this series range from atomic number 89 (actinium) through 103 (lawrencium). Actiniums most stable isotope is actinium-227, with a half-life of about 22 years. It decays into Fr-223 by alpha decay and Th-227 through beta decay, and both of these isotopes are decay products from uranium-235. 

Uranium is the fourth metal in the actinide series. It looks much like other actinide metallic elements with a silvery luster. It is comparatively heavy, yet malleable and ductile. It reacts with air to form an oxide of uranium. It is one of the few naturally radioactive elements that is fissionable, meaning that as it absorbs more neutrons, it splits into a series of other lighter elements (lower atomic weights) through a process of alpha decay and beta emission that is known as the uranium decay series, as follows U-238—> Th-234—>Pa-234—>U-234—> Th-230 Ra-226 Rn-222 Po-218 Pb-2l4 At-218 Bi-2l4 Rn-218 Po-2l4 Ti-210—>Pb-210—>Bi-210 Ti-206—>Pb-206 (stable isotope of lead,... 

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. 

The transactinide series of elements (Z-104 to Z-113) are those elements that follow the actinide series (Z-89 to Z-103) and proceed to the superactinides, some of which are yet to be discovered. (Note Z is the symbol used to represent the atomic numbers [protons] of elements in the transactinide series, as well as of other elements.) All elements of the transactinide series are radioactive, heavy metals that are unstable, and they usually decay by spontaneous fission or alpha decay into smaller nuclei of elements with less mass. 

The first actinide metals to be prepared were those of the three members of the actinide series present in nature in macro amounts, namely, thorium (Th), protactinium (Pa), and uranium (U). Until the discovery of neptunium (Np) and plutonium (Pu) and the subsequent manufacture of milligram amounts of these metals during the hectic World War II years (i.e., the early 1940s), no other actinide element was known. The demand for Pu metal for military purposes resulted in rapid development of preparative methods and considerable study of the chemical and physical properties of the other actinide metals in order to obtain basic knowledge of these unusual metallic elements. 

Symbol Pa atomic number 91 atomic weight 231.04 an actinide series radioactive element an inner-transition metal electron configuration [Rn]5/26di7s2 valence states +4 and +5 atomic radius 1.63A (for coordination number 12) twenty-two isotopes are known in the mass range 215-218,... 

Most transition metals of the three d-series in all their valency states exhibit ionic radii within the limits of 0.55 and 0.86 A, favourable to octahedral coordination. In fact higher coordination numbers are observed only in fluorides of the largest transition ions, above all in compounds of the lanthanide and actinide series. Therefore fluorides of those elements, though sometimes isostructural with compounds of the d-series, will not be discussed here. For information the books and reviews written by Spedding and Daane (291), Katz and Seaborg (181) and Kaiz and Sheft (182) may be consulted. 

The remaining exceptions concern the lanthanide series, where samarium at room temperature has a particular hexagonal structure and especially the lower actinides uranium, neptunium, and plutonium. Here the departure from simple symmetry is particularly pronounced. Comparing these three elements with other metals having partly filled inner shells (transition elements and lanthanides), U, Pu, Np have the lowest symmetry at room temperature, normal pressure. This particular crystallographic character is the reason why Pearson did not succeed to fit the alpha forms of U, Pu, and Np, as well as gamma-Pu into his comprehensive classification of metallic structures and treated them as idiosyncratic structures . Recent theoretical considerations reveal that the appearance of low symmetries in the actinide series is intimately linked to the behaviour of the 5f electrons. 

No photoemission spectra are unfortunately available for Np metal, in the tight actinide 5 f itinerant side, and on Cm, Bk, Cf, etc. on the heavy actinide 5 f localized side. It is worthwhile to stress the need for good photoelectron evidence on these systems in order to shed more light on the elemental actinide metals series. 

The main group metals are the most important, given the role of Na+, K+, and Ca + in bioelectrical excitability. The transition metals also have biological relevance. A formal definition of transition metals is that they have partially filled d ox f orbitals in either their free (uncombined) atoms or one or more of their ions. Transition metals may be divided into t/-block and /-block elements the /-block is further divided into the lanthanide and actinide series. Since/-block metals are not of great significance to medicinal... 

A table of crystal structures for the elements can be found in Table 1.11 (excluding the Lanthanide and Actinide series). Some elements can have multiple crystal structures, depending on temperature and pressure. This phenomenon is called allotropy and is very common in elemental metals (see Table 1.12). It is not unusual for close-packed crystals to transform from one stacking sequence to the other, simply through a shift in one of the layers of atoms. Other common allotropes include carbon (graphite at ambient conditions, diamond at high pressures and temperature), pure iron (BCC at room temperature, FCC at 912°C and back to BCC at 1394°C), and titanium (HCP to BCC at 882°C). 

U is a member of the actinide series of elements which, together with the rare earths and the transition elements, possess a high heat of oxidation, a low oxide density compared with that of the metal, and the presence of an unfilled d shell in its electronic structure. While the reasons for the high pyrophoric potential of U are not clearly understood, they are thought to be related to these aforementioned properties (see under Pyrotechnics in Vol 8, P511 and Pyrophoric Incendiary Agents , P503-L)... 

Plutonium [7440-07-5], Pu, element number 94 in the Periodic Table, is a member of the actinide series and is metallic (see Actinides and transactinides). Isotopes of mass number 232 through 246 have been identified. All are radioactive. The most important isotope is plutonium-239 [15117-48-3]y 239Pu also of importance are 238Pu, 242Pu, and 244Pu. 

ACTINIDE CONTRACTION. An effect analogous to the Lanthanide contraction, which lias been found in certain elements of the Actinide series. Those elements from thorium (atomic number 90) to curium (atomic number 96) exhibit a decreasing molecular volume in certain compounds, such as those which the actinide tetrafluoiides form with alkali metal fluorides, plotted in Eig. 1. The effect here is due to the decreasing crystal radius of the tetrapositive actinide ions as the atomic number increases. Note that in the Actinides the tetravalent ions are compared instead of the trivalent ones as in the case of the Lanthanides, in which the trivalent state is by far the most common. 

BERKELIUM. [CAS 7440-40-6]. Chemical element, symbol Bk, at. no. 97, at wt. 247 (mass number of the most stable isotope), radioactive metal of the Actinide series, also one of the Transuranium elements. All isotopes of berkelium are radioactive all must be produced synthetically. The element was discovered by G.T. Seaborg and associates at the Metallurgical Laboratory of the University of Chicago in 1949. At that time, the dement was produced by bombarding 241 Am with helium ions. 4i Bk is an alpha-emitter and may be obtained by alpha-bombardment of ,4Cm. 245Cm. or 246Ciu. Ollier nuclides include those of mass numbers 243—246 and 248-250. Probable electronic configuration ... 

EINSTENIUM. CAS 7429-92-71. Chemical element symbol Es, at. no. 99. at. wt. 254 (mass number of the most stable isotope), radioactive metal of the Actinide series, also one of the Transuranium elements. Both einsteinium and fermium were formed tit a thermonuclear explosion that occurred in the South Pacific in 1952. The elements were identified by scientists from the University of California s Radiation Laboratory- the Argonnc National Laboratory, and the I. os Alamos Scientific Laboratory. It was observed that very heavy uranium isotopes which resulted from the action of the instantaneous neutron dux on uranium (contained in the explosive device) decayed to form Es and Fm. The probable electronic configuration of Es is... 

LANTHANIDE SERIES. The chemical elements with atomic numbers 58 to 71 inclusive, commencing with cerium t.5K)and through lutetiuni 171) frequently ate termed collectively, the Lanthanide Scries. Lanthanum, the anchor element of the series, appears in group 3h of the periodic table. Some authorities eonsider lanthanum a part of the series. Members ol the series, along with lanthanum and yttrium, are described under Rare-Earth Elements and Metals. See also Actinide Series. 

LAWRENCTUM. CAS 22537-I9-5. Chemical element, symbol Lr. at. no. 103. at. wl. 257 (mass number ol known isotope), rudiouclivc metal of the Actinide series, also one of the Transuranium elements. ""Lr was identified in 1961 by A. Ghiorso. T. Sikkelaiul. A. Larsh. and K. Latimer at the University of California ai Berkeley. 

PROTACTINIUM. [CAS 7440-13-13], Chemical element, symbol Pa, at. no. 91, at. wt, 231.036, radioactive metal of the Actinide Series, mp is estimated at less than 1600°C, All isotopes arc radioactive. The most stable isotope is 23IPa with a half-life of 3,43 v 104 years, The latter is a second-generation daughter of a5U and a member of the actinium (2n + 3) decay series, See also Radioactivity, Electronic configuration... 

RARE-EARTH ELEMENTS AND METALS. Sometimes referred to as the fraternal fifteen," because of similarities in physical and chemical properties, the rare-earth elements actually are not so rare. This is attested by Fig. 1, which shows a dry lake bed in California that alone contains well in excess of one million pounds of two of die elements, neodymium and praseodymium. The world s largest rare earth body and mine near Baotou, Inner Mongolia, China is shown in Fig. 2. It contains 25 million tons of rare earth oxides (about one quarter of the world s human reserves. The term rare arises from the fact that these elements were discovered in scarce materials. The term earth stems from die tact that the elements were first isolated from their ores in the chemical form of oxides and that the old chemical terminology for oxide is earth. The rare-earth elements, also termed Lanthanides, are similar in that they share a valence of 3 and are treated as a separate side branch of the periodic table, much like die Actinides. See also Actinide Contraction Chemical Elements Lanthanide Series and Periodic Table of the Elements. 

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