Actinium atomic properties

URANIUM compounds), Pb from the thorium series, and Pb from the actinium series (see Actinides and transactinides). The crystal stmcture of lead is face-centered cubic the length of the edge of the cell is 0.49389 nm the number of atoms per unit cell is four. Other properties are Hsted in Table 1. 

These two kinds of lead are now known to be isotopes, or inseparable elements which belong in the same space in the periodic table and yet differ in atomic weight and in radioactive properties. According to Frederick Soddy, the first clear recognition of isotopes as chemically inseparable substances was that of H. N. McCoy and W. H. Ross in 1907 (75,107). Strictly speaking, the science of radioactivity has revealed only five naturally occurring new elements with distinctive physical and chemical properties polonium, thoron, radium, actinium, and uranium X2. All the other natural radioactive elements share previously occupied places in the periodic table. 

Elements 43, Masurium 61, Illinium 84, Polonium or Radium F 89, Actinium 91, Uranium Xs do not appear in the atomic weight tables. Although their existence has been indicated by means of X-rays or radioactive properties, they have not been isolated in amounts to allow of atomic weight determination. 

All these new discoveries, of course, verified Seaborg s theory, and the transuranium elements, along with thorium, protactinium and uranium, are now called the actinide elements. They all fit in the Periodic Table between actinium and the element eka-hafnium. Eka-hafnium is the tentative name given to the undiscovered element with the atomic number 104 which lies directly below hafnium in the Periodic Table and which is expected to have chemical properties similar to those of hafnium. 

Now the fact that the actinide elements are all chemically similar to actinium reminds us of another fact, that the chemical properties of an element are largely traceable to the number of electrons in an atom s outer electron shell. 

As early as 1923 N. Bohr suggested that there might exist a group of IS elements at the end of the Periodic Table Uiat would be analogous in their properties to the IS lanthanide ("rare earth") elemrats. This idea, combined with the increasing stability of the -t-3 oxidation state for the transuranium elem ts as the atomic number increases from Z = 93 to 96, led Seaborg to the conclusion that these new elemrats constituted a second rare earth series whose initial member was actinium. As the atomic number increases from 90, electrons are added in the Sf subshell similar to the occupation of the 4f subshell in the lanthanides, see Table 16.1. This series would be terminated with element 103 since this would correspond to the addition of 14 electrons for a completed Sf subshell. 

Americium and curium were placed after actinium in the actinide series in the Periodic Table because their chemical properties were similar. Since that time, elements with atomic numbers to 118 have been reported by scientists around the world. 

I considered all of the evidence, especially the chemical properties of the elements with the atomic numbers 93 and 94, and made the suggestion that a rare-earth-like series begins with actinium in the same sense that the rare-earth or lanthanide series begins with lanthanum. On this basis it might be termed the actinide series and the first 5f electron might - although would not necessarily - appear in thorium. The salient point is that the characteristic oxidation state would be the III state. 

The periodic table of elements is divided into horizontal rows and vertical colunuis. Elements in a particular column have similar chemical behaviom. Looking at the periodic table, the metals are in Row 2 (lithium, beryllium), Row 3 (sodimn, magnesium, aluminium), Row 4 (potassium, K through to gallium, Ga), Row 5 (rubidimn through to tin), Row 6 (caesium to bismuth) and Row 7 (francium to actinium). There are two special series of metals from atomic number 58-71 and 89-103. The first are the rare earth metals and the second the radioactive metals (those beyond 92 do not occur naturalfy). Nos 90 and 92 occur naturally and are used for atomic power. The rest of the elements in the table ate non-metals. Some have some metal-like properties and are called metalloids, e.g. nos 5, 14, 32, 33, 51, 52, 84 and 85. 

The elements in the group III B scandium, yttrium, lanthanum and actinium that have an incompletely filled d subshell in their atomic state (n - l)d ns. Although both lanthanum and actinium could be included in the d transition metal series, they are very similar physically and chemically to the elements in the f-block and therefore are considered to be f-type transition elements (4f-, 5f-type transition elements, respectively). The last element of the lanthanides series, lutetium, also has a partly filled d orbital (Table 2.6) and could also be included in the d transition metal group. However, it has similar properties to the 4f-type transition metals, where it is usually grouped with lanthanum and the rest of the lanthanides series. 

The two rows at the bottom of the periodic table that have been separated from the rest of the table are called lanthanides and actinides. The lanthanides, the elements in the first row, from cerium (Ce) to lutetium (Lu), are called the lanthanides because their properties are similar to those of lanthanum (La). Historically, they have also been called the rare earths because they were believed to be much rarer than other metals. The elements in the second row, from thorium (Th) to lawrencium (Lr), are called the actinides because they are similar to actinium (Ac). Notice that the atomic numbers of the lanthanides all fit between numbers 57 (La) and 72 (Hf). The atomic numbers of the actinides all fit between numbers 89 (Ac) and 104 (Rf). 

The actinoid series encompasses the fourteen chemical elements with atomic numbers from 90 to 103, thorium (Th) to lawrencium (Lr). The actinoid series derives its name from the group-IIla element actinium (Ac) which can be included in the series for the purpose of comparison. Only Th and uranium (U) occur in usable quantities in nature. The other actinoids are man-made elements. Pure Th is a silvery-white metal which is air-stable and retains its luster for several months. U exhibits three crystallographic modifications as follows a (688°C) —> P (776°C) —> U is a heavy, silvery-white metal. The luster of freshly prepared americium (Am) is white and more silvery than neptunium (Np) or plutonium (Pu) prepared in the same manner. All actinoid elements are radioactive. Table 2.113 sutnmarizes some physical properties of actinoid metals (Th, U and Am). 

Critical efforts to compile and to assess actinide thermodynamic properties have improved in more recent years. Krestov [10] prepared an extensive compilation of rare-earth and actinide thermochemical properties. Rand [11] comprehensively and critically reviewed thorium thermodynamics, and the thermodynamics group of the US National Bureau of Standards [12] published the final volume of the Technical Note 270 series, which included the elements actinium through uranium. At nearly the same time the parallel compendium of Glushko et al. [13] was published in the USSR. The most contemporary and thoroughly annotated compilation is the fourteen-part series issued under the auspices of the International Atomic Energy Agency, 7%e Chemical Thermodynamics of Actinide Elements and Compounds, of which nine volumes [14-21, 354] have been published as of the time of writing. 

Inner transition metals The final electrons of the iimer transition metals enter an f sublevel. The inner transition metals are placed below the main body of the periodic table. They include the lanthanide series, which are in period 6 and follow the element lanthanum, and the actinide series, which are in period 7 and follow actinium. The lanthanides have very similar properties and are silvery metals with relatively high melting points. They are used in welder s glasses, television screens, and lasers. The actinides are all radioactive, and most are synthetic elements. They include the transuranium elements, which are elements that have an atomic number greater than 92. 

PRACTICE EXAMPLE A Francium (Z = 87) is an extremely rare radioactive element formed when actinium (Z = 89) undergoes alpha-particle emission. Francium occurs in natural uranium minerals, but estimates are that little more than 15 g of francium exists in the top 1 km of Earth s crust. Few of francium s properties have been measured, but some can be inferred from its position in the periodic table. Estimate the melting point, density, and atomic (metallic) radius of francium. [Hint Plot each property versus atomic number, Z, and extrapolate to Z = 87.]... 

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